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Network Working Group                                            M. KaeoRequest for Comments: 4778                    Double Shot Security, Inc.Category: Informational                                     January 2007Current Operational Security Practices inInternet Service Provider EnvironmentsStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The IETF Trust (2007).Abstract   This document is a survey of the current practices used in today's   large ISP operational networks to secure layer 2 and layer 3   infrastructure devices.  The information listed here is the result of   information gathered from people directly responsible for defining   and implementing secure infrastructures in Internet Service Provider   environments.Kaeo                         Informational                      [Page 1]

RFC 4778                    OPSEC Practices                 January 2007Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Scope  . . . . . . . . . . . . . . . . . . . . . . . . . .21.2.  Threat Model . . . . . . . . . . . . . . . . . . . . . . .31.3.  Attack Sources . . . . . . . . . . . . . . . . . . . . . .41.4.  Operational Security Impact from Threats . . . . . . . . .51.5.  Document Layout  . . . . . . . . . . . . . . . . . . . . .72.  Protected Operational Functions  . . . . . . . . . . . . . . .82.1.  Device Physical Access . . . . . . . . . . . . . . . . . .82.2.  Device Management - In-Band and Out-of-Band (OOB)  . . . .102.3.  Data Path  . . . . . . . . . . . . . . . . . . . . . . . .162.4.  Routing Control Plane  . . . . . . . . . . . . . . . . . .18     2.5.  Software Upgrades and Configuration           Integrity/Validation . . . . . . . . . . . . . . . . . . .222.6.  Logging Considerations . . . . . . . . . . . . . . . . . .262.7.  Filtering Considerations . . . . . . . . . . . . . . . . .292.8.  Denial-of-Service Tracking/Tracing . . . . . . . . . . . .303.  Security Considerations  . . . . . . . . . . . . . . . . . . .324.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .325.  References . . . . . . . . . . . . . . . . . . . . . . . . . .335.1.  Normative References . . . . . . . . . . . . . . . . . . .335.2.  Informational References . . . . . . . . . . . . . . . . .33Appendix A.  Protocol Specific Attacks . . . . . . . . . . . . . .34A.1.  Layer 2 Attacks  . . . . . . . . . . . . . . . . . . . . .34A.2.  IPv4 Protocol-Based Attacks  . . . . . . . . . . . . . . .34A.3.  IPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . .361.  Introduction   Security practices are well understood by the network operators who   have, for many years, gone through the growing pains of securing   their network infrastructures.  However, there does not exist a   written document that enumerates these security practices.  Network   attacks are continually increasing and although it is not necessarily   the role of an ISP to act as the Internet police, each ISP has to   ensure that certain security practices are followed to ensure that   their network is operationally available for their customers.  This   document is the result of a survey conducted to find out what current   security practices are being deployed to secure network   infrastructures.1.1.  Scope   The scope for this survey is restricted to security practices that   mitigate exposure to risks with the potential to adversely impact   network availability and reliability.  Securing the actual data   traffic is outside the scope of the conducted survey.  This documentKaeo                         Informational                      [Page 2]

RFC 4778                    OPSEC Practices                 January 2007   focuses solely on documenting currently deployed security mechanisms   for layer 2 and layer 3 network infrastructure devices.  Although   primarily focused on IPv4, many of the same practices can (and   should) apply to IPv6 networks.  Both IPv4 and IPv6 network   infrastructures are taken into account in this survey.1.2.  Threat Model   A threat is a potential for a security violation, which exists when   there is a circumstance, capability, action, or event that could   breach security and cause harm [RFC2828].  Every operational network   is subject to a multitude of threat actions, or attacks, i.e., an   assault on system security that derives from an intelligent act that   is a deliberate attempt to evade security services, and violate the   security policy of a system [RFC2828].  Many of the threats to a   network infrastructure occur from an instantiation (or combination)   of the following:   Reconnaissance: An attack whereby information is gathered to   ascertain the network topology or specific device information, which   can be further used to exploit known vulnerabilities   Man-In-The-Middle: An attack where a malicious user impersonates   either the sender or recipient of a communication stream while   inserting, modifying, or dropping certain traffic.  This type of   attack also covers phishing and session hijacks.   Protocol Vulnerability Exploitation: An attack that takes advantage   of known protocol vulnerabilities due to design or implementation   flaws to cause inappropriate behavior.   Message Insertion: This can be a valid message (it could be a reply   attack, which is a scenario where a message is captured and resent at   a later time).  A message can also be inserted with any of the fields   in the message being spoofed, such as IP addresses, port numbers,   header fields, or even packet content.  Flooding is also part of this   threat instantiation.   Message Diversion/Deletion: An attack where legitimate messages are   removed before they can reach the desired recipient, or are   re-directed to a network segment that is normally not part of the   data path.   Message Modification: This is a subset of a message insertion attack   where a previous message has been captured and modified before being   retransmitted.  The message can be captured using a man-in-the-middle   attack or message diversion.Kaeo                         Informational                      [Page 3]

RFC 4778                    OPSEC Practices                 January 2007   Note that sometimes denial-of-service attacks are listed as separate   categories.  A denial-of-service is a consequence of an attack and   can be the result of too much traffic (i.e., flooding), exploiting   protocol exploitation, or inserting/deleting/diverting/modifying   messages.1.3.  Attack Sources   These attacks can be sourced in a variety of ways:   Active vs Passive Attacks      An active attack involves writing data to the network.  It is      common practice in active attacks to disguise one's address and      conceal the identity of the traffic sender.  A passive attack      involves only reading information off the network.  This is      possible if the attacker has control of a host in the      communications path between two victim machines, or has      compromised the routing infrastructure to specifically arrange      that traffic pass through a compromised machine.  There are also      situations where mirrored traffic (often used for debugging,      performance monitoring, or accounting purposes) is diverted to a      compromised machine, which would not necessarily subvert any      existing topology, and could be harder to detect.  In general, the      goal of a passive attack is to obtain information that the sender      and receiver would prefer to remain private [RFC3552].   On-path vs Off-path Attacks      In order for a datagram to be transmitted from one host to      another, it generally must traverse some set of intermediate links      and routers.  Such routers are naturally able to read, modify, or      remove any datagram transmitted along that path.  This makes it      much easier to mount a wide variety of attacks if you are on-path.      Off-path hosts can transmit arbitrary datagrams that appear to      come from any host but cannot necessarily receive datagrams      intended for other hosts.  Thus, if an attack depends on being      able to receive data, off-path hosts must first subvert the      topology in order to place themselves on-path.  This is by no      means impossible, but is not necessarily trivial [RFC3552].  A      more subtle attack is one where the traffic-mirroring capability      of a device is hijacked and the traffic is diverted to a      compromised host since the network topology may not need to be      subverted.Kaeo                         Informational                      [Page 4]

RFC 4778                    OPSEC Practices                 January 2007   Insider vs Outsider Attacks      An "insider attack" is initiated from inside a given security      perimeter by an entity that is authorized to access system      resources, but uses them in a way not approved by those who      granted the authorization.  An "outside attack" is initiated from      outside the perimeter by an unauthorized or illegitimate user of      the system.   Deliberate Attacks vs Unintentional Events      A deliberate attack is where a miscreant intentionally performs an      assault on system security.  However, there are also instances      where unintentional events cause the same harm, yet are performed      without malicious intent.  Configuration errors and software bugs      can be as devastating to network availability as any deliberate      attack on the network infrastructure.   The attack source can be a combination of any of the above, all of   which need to be considered when trying to ascertain the impact any   attack can have on the availability and reliability of the network.   It is nearly impossible to stop insider attacks or unintentional   events.  However, if appropriate monitoring mechanisms are in place,   these attacks can also be detected and mitigated as with any other   attack source.  The amount of effort it takes to identify and trace   an attack is, of course, dependent on the resourcefulness of the   attacker.  Any of the specific attacks discussed further in this   document will elaborate on malicious behavior, which are sourced by   an "outsider" and are deliberate attacks.  Some further elaboration   will be given to the feasibility of passive vs active and on-path vs   off-path attacks to show the motivation behind deploying certain   security features.1.4.  Operational Security Impact from Threats   The main concern for any of the potential attack scenarios is the   impact and harm it can cause to the network infrastructure.  The   threat consequences are the security violations that results from a   threat action, i.e., an attack.  These are typically classified as   follows:   (Unauthorized) Disclosure      A circumstance or event whereby an entity gains access to data for      which the entity is not authorized.Kaeo                         Informational                      [Page 5]

RFC 4778                    OPSEC Practices                 January 2007   Deception      A circumstance or event that may result in an authorized entity      receiving false data and believing it to be true.   Disruption      A circumstance or event that interrupts or prevents the correct      operation of system services and functions.  A broad variety of      attacks, collectively called denial of service attacks, threaten      the availability of systems and bandwidth to legitimate users.      Many such attacks are designed to consume machine resources,      making it difficult or impossible to serve legitimate users.      Other attacks cause the target machine to crash, completely      denying service to users.   Usurpation      A circumstance or event that results in control of system services      or functions by an unauthorized entity.  Most network      infrastructure systems are only intended to be completely      accessible to certain authorized individuals.  Should an      unauthorized person gain access to critical layer 2/layer 3      infrastructure devices or services, they could cause great harm to      the reliability and availability of the network.   A complete description of threat actions that can cause these threat   consequences can be found in [RFC2828].  Typically, a number of   different network attacks are used in combination to cause one or   more of the above-mentioned threat consequences.  An example would be   a malicious user who has the capability to eavesdrop on traffic.   First, he may listen in on traffic for a while, doing reconnaissance   work and ascertaining which IP addresses belong to specific devices,   such as routers.  Were this miscreant to obtain information, such as   a router password sent in cleartext, he can then proceed to   compromise the actual router.  From there, the miscreant can launch   various active attacks, such as sending bogus routing updates to   redirect traffic or capture additional traffic to compromise other   network devices.  While this document enumerates which   countermeasures ISPs are deploying today, a useful generic analysis   of actual backbone infrastructure attacks and the appropriate   countermeasures can be found in [RTGWG].Kaeo                         Informational                      [Page 6]

RFC 4778                    OPSEC Practices                 January 20071.5.  Document Layout   This document is a survey of current operational practices that   mitigate the risk of being susceptible to any threat actions.  As   such, the main focus is on the currently deployed security practices   used to detect and/or mitigate attacks.  The top-level categories in   this document are based on operational functions for ISPs and   generally relate to what is to be protected.  This is followed by a   description of which attacks are possible and the security practices   currently deployed.  This will provide the necessary security   services to help mitigate these attacks.  These security services are   classified as follows:   o  User Authentication   o  User Authorization   o  Data Origin Authentication   o  Access Control   o  Data Integrity   o  Data Confidentiality   o  Auditing/Logging   o  DoS Mitigation   In many instances, a specific protocol currently deployed will offer   a combination of these services.  For example, Authentication,   Authorization, and Accounting (AAA) can offer user authentication,   user authorization, and audit/logging services, while the Secure   SHell (SSH) Protocol can provide data origin authentication, data   integrity, and data confidentiality.  The services offered are more   important than the actual protocol used.  Note that access control   will refer basically to logical access control, i.e., filtering.   Each section ends with an additional considerations section that   explains why specific protocols may or may not be used, and also   gives some information regarding capabilities, which are not possible   today due to bugs or lack of usability.Kaeo                         Informational                      [Page 7]

RFC 4778                    OPSEC Practices                 January 20072.  Protected Operational Functions2.1.  Device Physical Access   Device physical access pertains to protecting the physical location   and access of the layer 2 or layer 3 network infrastructure device.   Physical security is a large field of study/practice in and of   itself, arguably the largest, oldest, and most well-understood area   of security.  Although it is important to have contingency plans for   natural disasters, such as earthquakes and floods, which can cause   damage to networking devices, this is out of the scope of this   document.  Here, we concern ourselves with protecting access to the   physical location and how a device can be further protected from   unauthorized access if the physical location has been compromised,   i.e., protecting the console access.  This is aimed largely at   stopping an intruder with physical access from gaining operational   control of the device(s).  Note that nothing will stop an attacker   with physical access from effecting a denial-of-service attack, which   can be easily accomplished by powering off the device or just   unplugging some cables.2.1.1.  Threats/Attacks   If any intruder gets physical access to a layer 2 or layer 3 device,   the entire network infrastructure can be under the control of the   intruder.  At a minimum, the intruder can take the compromised device   out of service, causing network disruption, the extent of which   depends on the network topology.  A worse scenario is where the   intruder uses this device to crack the console password, gaining   complete control of the device (perhaps without anyone detecting such   a compromise, or to attach another network device onto a port and   siphon off data with which the intruder can ascertain the network   topology) and the entire network.   The threat of gaining physical access can be realized in a variety of   ways, even if critical devices are under high security.  Cases still   occur where attackers have impersonated maintenance workers to gain   physical access to critical devices that have caused major outages   and privacy compromises.  Insider attacks from authorized personnel   also pose a real threat and must be adequately recognized and   addressed.2.1.2.  Security Practices   For physical device security, equipment is kept in highly restrictive   environments.  Only authorized users with card-key badges have access   to any of the physical locations that contain critical network   infrastructure devices.  These card-key systems keep track of whoKaeo                         Informational                      [Page 8]

RFC 4778                    OPSEC Practices                 January 2007   accessed which location and at what time.  Most cardkey systems have   a fail-back "master key" in case the card system is down.  This   "master key" usually has limited access and its use is also carefully   logged (which should only happen if the card-key system is NOT   online/functional).   All console access is always password protected and the login time is   set to time out after a specified amount of inactivity - typically   between 3-10 minutes.  The type of privileges that you obtain from a   console login varies between separate vendor devices.  In some cases   you get initial basic access and need to perform a second   authentication step to get more privileged access (i.e., enable or   root).  In other vendors, you get the more privileged access when you   log into the console as root, without requiring a second   authentication step.   How ISPs manage these logins vary greatly, although many of the   larger ISPs employ some sort of AAA mechanism to help automate   privilege-level authorization and utilize the automation to bypass   the need for a second authentication step.  Also, many ISPs define   separate classes of users to have different privileges while logged   onto the console.  Typically, all console access is provided via an   out-of-band (OOB) management infrastructure, which is discussed inSection 2.2 of this document.2.1.3.  Security Services   The following security services are offered through the use of the   practices described in the previous section:   o  User Authentication - All individuals who have access to the      physical facility are authenticated.  Console access is      authenticated.   o  User Authorization - An authenticated individual has implicit      authorization to perform commands on the device.  In some cases,      multiple authentication is required to differentiate between basic      and more privileged access.   o  Data Origin Authentication - Not applicable.   o  Access Control - Not applicable.   o  Data Integrity - Not applicable.   o  Data Confidentiality - Not applicable.Kaeo                         Informational                      [Page 9]

RFC 4778                    OPSEC Practices                 January 2007   o  Auditing/Logging - All access to the physical locations of the      infrastructure equipment is logged via electronic card-key      systems.  All console access is logged (refer toSection 2.2 of      this document for more details).   o  DoS Mitigation - Not applicable.2.1.4.  Additional Considerations   Physical security is relevant to operational security practices as   described in this document, mostly from a console-access perspective.   Most ISPs provide console access via an OOB management   infrastructure, which is discussed inSection 2.2 of this document.   The physical and logical authentication and logging systems should be   run independently of each other and should reside in different   physical locations.  These systems need to be secured to ensure that   they themselves will not be compromised, which could give the   intruder valuable authentication and logging information.   Social engineering plays a big role in many physical access   compromises.  Most ISPs have set up training classes and awareness   programs to educate company personnel to deny physical access to   people who are not properly authenticated or authorized to have   physical access to critical infrastructure devices.2.2.  Device Management - In-Band and Out-of-Band (OOB)   In-band management is generally considered to be device access, where   the control traffic takes the same data path as the data that   traverses the network.  Out-of-band management is generally   considered to be device access, where the control traffic takes a   separate path as the data that traverses the network.  In many   environments, device management for layer 2 and layer 3   infrastructure devices is deployed as part of an out-of-band   management infrastructure, although there are some instances where it   is deployed in-band as well.  Note that while many of the security   concerns and practices are the same for OOB management and in-band   management, most ISPs prefer an OOB management system, since access   to the devices that make up this management network are more   vigilantly protected and considered to be less susceptible to   malicious activity.   Console access is always architected via an OOB network.  Presently,   the mechanisms used for either in-band management or OOB are via   virtual terminal access (i.e., Telnet or SSH), Simple Network   Management Protocol (SNMP), or HTTP.  In all large ISPs that were   interviewed, HTTP management was never used and was explicitlyKaeo                         Informational                     [Page 10]

RFC 4778                    OPSEC Practices                 January 2007   disabled.  Note that file transfer protocols (TFTP, FTP, and SCP)   will be covered inSection 2.5 of this document.2.2.1.  Threats/Attacks   For device management, passive attacks are possible if someone has   the capability to intercept data between the management device and   the managed device.  The threat is possible if a single   infrastructure device is somehow compromised and can act as a network   sniffer, or if it is possible to insert a new device that acts as a   network sniffer.   Active attacks are possible for both on-path and off-path scenarios.   For on-path active attacks, the situation is the same as for a   passive attack, where either a device has to already be compromised   or a device can be inserted into the path.  For off-path active   attacks, where a topology subversion is required to reroute traffic   and essentially bring the attacker on-path, the attack is generally   limited to message insertion or modification.2.2.1.1.  Confidentiality Violations   Confidentiality violations can occur when a miscreant intercepts any   management data that has been sent in cleartext or with weak   encryption.  This includes interception of usernames and passwords   with which an intruder can obtain unauthorized access to network   devices.  It can also include other information, such as logging or   configuration information, if an administrator is remotely viewing   local logfiles or configuration information.2.2.1.2.  Offline Cryptographic Attacks   If username/password information was encrypted but the cryptographic   mechanism used made it easy to capture data and break the encryption   key, the device management traffic could be compromised.  The traffic   would need to be captured either by eavesdropping on the network or   by being able to divert traffic to a malicious user.2.2.1.3.  Replay Attacks   For a replay attack to be successful, the management traffic would   need to first be captured either on-path or diverted to an attacker   to later be replayed to the intended recipient.Kaeo                         Informational                     [Page 11]

RFC 4778                    OPSEC Practices                 January 20072.2.1.4.  Message Insertion/Deletion/Modification   Data can be manipulated by someone in control of intermediary hosts.   Forging data is also possible with IP spoofing, where a remote host   sends out packets that appear to come from another, trusted host.2.2.1.5.  Man-In-The-Middle   A man-in-the-middle attack attacks the identity of a communicating   peer rather than the data stream itself.  The attacker intercepts   traffic that is sent from a management system to the networking   infrastructure device and traffic that is sent from the network   infrastructure device to the management system.2.2.2.  Security Practices   OOB management is done via a terminal server at each location.  SSH   access is used to get to the terminal server from where sessions to   the devices are initiated.  Dial-in access is deployed as a backup if   the network is not available.  However, it is common to use dial-   back, encrypting modems, and/or one-time-password (OTP) modems to   avoid the security weaknesses of plain dial-in access.   All in-band management and OOB management access to layer 2 and layer   3 devices is authenticated.  The user authentication and   authorization is typically controlled by an AAA server (i.e., Remote   Authentication Dial-in User Service (RADIUS) and/or Terminal Access   Controller Access-Control System (TACACS+)).  Credentials used to   determine the identity of the user vary from static username/password   to one-time username/password schemes such as Secure-ID.  Static   username/passwords are expired after a specified period of time,   usually 30 days.  Every authenticated entity via AAA is an individual   user for greater granularity of control.  Note that often the AAA   server used for OOB management authentication is a separate physical   device from the AAA server used for in-band management user   authentication.  In some deployments, the AAA servers used for device   management authentication/authorization/accounting are on separate   networks to provide a demarcation for any other authentication   functions.   For backup purposes, there is often a single local database entry for   authentication that is known to a very limited set of key personnel.   It is usually the highest privilege-level username/password   combination, which in most cases is the same across all devices.   This local device password is routinely regenerated once every 2-3   months, and is also regenerated immediately after an employee who had   access to that password leaves the company or is no longer authorized   to have knowledge of that password.Kaeo                         Informational                     [Page 12]

RFC 4778                    OPSEC Practices                 January 2007   Each individual user in the AAA database is configured with specific   authorization capability.  Specific commands are either individually   denied or permitted, depending on the capability of the device to be   accessed.  Multiple privilege levels are deployed.  Most individuals   are authorized with basic authorization to perform a minimal set of   commands, while a subset of individuals are authorized to perform   more privileged commands.  Securing the AAA server is imperative and   access to the AAA server itself is strictly controlled.  When an   individual leaves the company, his/her AAA account is immediately   deleted and the TACACS/RADIUS shared secret is reset for all devices.   Some management functions are performed using command line interface   (CLI) scripting.  In these scenarios, a dedicated user is used for   the identity in scripts that perform CLI scripting.  Once   authenticated, these scripts control which commands are legitimate,   depending on authorization rights of the authenticated individual.   SSH is always used for virtual terminal access to provide for an   encrypted communication channel.  There are exceptions due to   equipment limitations which are described in the additional   considerations section.   If SNMP is used for management, it is for read queries only and   restricted to specific hosts.  If possible, the view is also   restricted to only send the information that the management station   needs, rather than expose the entire configuration file with the   read-only SNMP community.  The community strings are carefully chosen   to be difficult to crack and there are procedures in place to change   these community strings between 30-90 days.  If systems support two   SNMP community strings, the old string is replaced by first   configuring a second, newer community string and then migrating over   from the currently used string to the newer one.  Most large ISPs   have multiple SNMP systems accessing their routers so it takes more   then one maintenance period to get all the strings fixed in all the   right systems.  SNMP RW is not used and is disabled by configuration.   Access control is strictly enforced for infrastructure devices by   using stringent filtering rules.  A limited set of IP addresses are   allowed to initiate connections to the infrastructure devices and are   specific to the services to which they are to limited (i.e., SSH and   SNMP).   All device management access is audited and any violations trigger   alarms that initiate automated email, pager, and/or telephone   notifications.  AAA servers keep track of the authenticated entity as   well as all the commands that were carried out on a specific device.   Additionally, the device itself logs any access control violations   (i.e., if an SSH request comes in from an IP address that is notKaeo                         Informational                     [Page 13]

RFC 4778                    OPSEC Practices                 January 2007   explicitly permitted, that event is logged so that the offending IP   address can be tracked down and investigations made as to why it was   trying to access a particular infrastructure device)2.2.3.  Security Services   The security services offered for device OOB management are nearly   identical to those of device in-band management.  Due to the critical   nature of controlling and limiting device access, many ISPs feel that   physically separating the management traffic from the normal customer   data traffic will provide an added level of risk mitigation and limit   the potential attack vectors.  The following security services are   offered through the use of the practices described in the previous   section:   o  User Authentication - All individuals are authenticated via AAA      services.   o  User Authorization - All individuals are authorized via AAA      services to perform specific operations once successfully      authenticated.   o  Data Origin Authentication - Management traffic is strictly      filtered to allow only specific IP addresses to have access to the      infrastructure devices.  This does not alleviate risk the from      spoofed traffic, although when combined with edge filtering usingBCP38 [RFC2827] andBCP84 [RFC3704] guidelines (discussed inSection 2.5), then the risk of spoofing is mitigated, barring a      compromised internal system.  Also, using SSH for device access      ensures that no one can spoof the traffic during the SSH session.   o  Access Control - Management traffic is filtered to allow only      specific IP addresses to have access to the infrastructure      devices.   o  Data Integrity - Using SSH provides data integrity and ensures      that no one has altered the management data in transit.   o  Data Confidentiality - Using SSH provides data confidentiality.   o  Auditing/Logging - Using AAA provides an audit trail for who      accessed which device and which operations were performed.   o  DoS Mitigation - Using packet filters to allow only specific IP      addresses to have access to the infrastructure devices.  This      limits but does not prevent spoofed DoS attacks directed at an      infrastructure device.  However, the risk is lowered by using a      separate physical network for management purposes.Kaeo                         Informational                     [Page 14]

RFC 4778                    OPSEC Practices                 January 20072.2.4.  Additional Considerations   Password selection for any device management protocol used is   critical to ensure that the passwords are hard to guess or break   using a brute-force attack.   IP security (IPsec) is considered too difficult to deploy, and the   common protocol to provide for confidential management access is SSH.   There are exceptions for using SSH due to equipment limitations since   SSH may not be supported on legacy equipment.  In some cases,   changing the host name of a device requires an SSH rekey event since   the key is based on some combination of host name, Message   Authentication Code (MAC) address, and time.  Also, in the case where   the SSH key is stored on a route processor card, a re-keying of SSH   would be required whenever the route processor card needs to be   swapped.  Some providers feel that this operational impact exceeds   the security necessary and instead use Telnet from trusted inside   hosts (called 'jumphosts' or 'bastion hosts') to manage those   devices.  An individual would first SSH to the jumphost and then   Telnet from the jumphost to the actual infrastructure device, fully   understanding that any passwords will be sent in the clear between   the jumphost and the device to which it is connecting.  All   authentication and authorization is still carried out using AAA   servers.   In instances where Telnet access is used, the logs on the AAA servers   are more verbose and more attention is paid to them to detect any   abnormal behavior.  The jumphosts themselves are carefully controlled   machines and usually have limited access.  Note that Telnet is NEVER   allowed to an infrastructure device except from specific jumphosts;   i.e., packet filters are used at the console server and/or   infrastructure device to ensure that Telnet is only allowed from   specific IP addresses.   With thousands of devices to manage, some ISPs have created automated   mechanisms to authenticate to devices.  As an example, Kerberos has   been used to automate the authentication process for devices that   have support for Kerberos.  An individual would first log in to a   Kerberized UNIX server using SSH and generate a Kerberos 'ticket'.   This 'ticket' is generally set to have a lifespan of 10 hours and is   used to automatically authenticate the individual to the   infrastructure devices.   In instances where SNMP is used, some legacy devices only support   SNMPv1, which then requires the provider to mandate its use across   all infrastructure devices for operational simplicity.  SNMPv2 is   primarily deployed since it is easier to set up than v3.Kaeo                         Informational                     [Page 15]

RFC 4778                    OPSEC Practices                 January 20072.3.  Data Path   This section refers to how traffic is handled that traverses the   network infrastructure device.  The primary goal of ISPs is to   forward customer traffic.  However, due to the large amount of   malicious traffic that can cause DoS attacks and render the network   unavailable, specific measures are sometimes deployed to ensure the   availability to forward legitimate customer traffic.2.3.1.  Threats/Attacks   Any data traffic can potentially be attack traffic and the challenge   is to detect and potentially stop forwarding any of the malicious   traffic.  The deliberately sourced attack traffic can consist of   packets with spoofed source and/or destination addresses or any other   malformed packet that mangle any portion of a header field to cause   protocol-related security issues (such as resetting connections,   causing unwelcome ICMP redirects, creating unwelcome IP options, or   packet fragmentations).2.3.2.  Security Practices   Filtering and rate limiting are the primary mechanism to provide risk   mitigation of malicious traffic rendering the ISP services   unavailable.  However, filtering and rate limiting of data path   traffic is deployed in a variety of ways, depending on how automated   the process is and what the capabilities and performance limitations   of the existing deployed hardware are.   The ISPs that do not have performance issues with their equipment   followBCP38 [RFC2827] andBCP84 [RFC3704] guidelines for ingress   filtering.BCP38 recommends filtering ingress packets with obviously   spoofed and/or 'reserved' source addresses to limit the effects of   denial-of-service attacks, whileBCP84 extends the recommendation for   multi-homed environments.  Filters are also used to help alleviate   issues between service providers.  Without any filtering, an   inter-exchange peer could steal transit just by using static routes,   and essentially redirect data traffic.  Therefore, some ISPs have   implemented ingress/egress filters that block unexpected source and   destination addresses not defined in the above-mentioned documents.   Null routes and black-hole triggered routing [RFC3882] are used to   deter any detected malicious traffic streams.  These two techniques   are described in more detail inSection 2.8 below.   Most ISPs consider layer 4 filtering useful, but it is only   implemented if performance limitations allow for it.  Since it poses   a large administrative overhead and ISPs are very much opposed to   acting as the Internet firewall, Layer 4 filtering is typicallyKaeo                         Informational                     [Page 16]

RFC 4778                    OPSEC Practices                 January 2007   implemented as a last option.  Netflow is used for tracking traffic   flows, but there is some concern whether sampling is good enough to   detect malicious behavior.   Unicast Reverse Path Forwarding (RPF) is not consistently   implemented.  Some ISPs are in the process of doing so, while other   ISPs think that the perceived benefit of knowing that spoofed traffic   comes from legitimate addresses are not worth the operational   complexity.  Some providers have a policy of implementing uRPF at   link speeds of Digital Signal 3 (DS3) and below, which was due to the   fact that all hardware in the network supported uRPF for DS3 speeds   and below.  At higher-speed links, the uRPF support was inconsistent   and it was easier for operational people to implement a consistent   solution.2.3.3.  Security Services   o  User Authentication - Not applicable.   o  User Authorization - Not applicable.   o  Data Origin Authentication - When IP address filtering perBCP38,BCP84, and uRPF are deployed at network edges it can ensure that      any spoofed traffic comes from at least a legitimate IP address      and can be tracked.   o  Access Control - IP address filtering and layer 4 filtering is      used to deny forbidden protocols and limit traffic destined for      infrastructure device itself.  Filters are also used to block      unexpected source/destination addresses.   o  Data Integrity - Not applicable.   o  Data Confidentiality - Not applicable.   o  Auditing/Logging - Filtering exceptions are logged for potential      attack traffic.   o  DoS Mitigation - Black-hole triggered filtering and rate-limiting      are used to limit the risk of DoS attacks.2.3.4.  Additional Considerations   For layer 2 devices, MAC address filtering and authentication is not   used in large-scale deployments.  This is due to the problems it can   cause when troubleshooting networking issues.  Port security becomes   unmanageable at a large scale where thousands of switches are   deployed.Kaeo                         Informational                     [Page 17]

RFC 4778                    OPSEC Practices                 January 2007   Rate limiting is used by some ISPs, although other ISPs believe it is   not really useful, since attackers are not well-behaved and it   doesn't provide any operational benefit over the complexity.  Some   ISPs feel that rate limiting can also make an attacker's job easier   by requiring the attacker to send less traffic to starve legitimate   traffic that is part of a rate limiting scheme.  Rate limiting may be   improved by developing flow-based rate-limiting capabilities with   filtering hooks.  This would improve the performance as well as the   granularity over current capabilities.   Lack of consistency regarding the ability to filter, especially with   respect to performance issues, cause some ISPs not to implementBCP38   andBCP84 guidelines for ingress filtering.  One such example is at   edge boxes, where up to 1000 T1s connecting into a router with an   OC-12 (Optical Carrier) uplink.  Some deployed devices experience a   large performance impact with filtering, which is unacceptable for   passing customer traffic through, though ingress filtering (uRPF)   might be applicable at the devices that are connecting these   aggregation routers.  Where performance is not an issue, the ISPs   make a tradeoff between management versus risk.2.4.  Routing Control Plane   The routing control plane deals with all the traffic that is part of   establishing and maintaining routing protocol information.2.4.1.  Threats/Attacks   Attacks on the routing control plane can be from both passive or   active sources.  Passive attacks are possible if someone has the   capability to intercept data between the communicating routing peers.   This can be accomplished if a single routing peer is somehow   compromised and can act as a network sniffer, or if it is possible to   insert a new device that acts as a network sniffer.   Active attacks are possible for both on-path and off-path scenarios.   For on-path active attacks, the situation is the same as for a   passive attack, where either a device has to already be compromised   or a device can be inserted into the path.  This may lead to an   attacker impersonating a legitimate routing peer and exchanging   routing information.  Unintentional active attacks are more common   due to configuration errors, which cause legitimate routing peers to   feed invalid routing information to other neighboring peers.   For off-path active attacks, the attacks are generally limited to   message insertion or modification, which can divert traffic to   illegitimate destinations, causing traffic to never reach its   intended destination.Kaeo                         Informational                     [Page 18]

RFC 4778                    OPSEC Practices                 January 20072.4.1.1.  Confidentiality Violations   Confidentiality violations can occur when a miscreant intercepts any   of the routing update traffic.  This is becoming more of a concern   because many ISPs are classifying addressing schemes and network   topologies as private and proprietary information.  It is also a   concern because the routing protocol packets contain information that   may show ways in which routing sessions could be spoofed or hijacked.   This in turn could lead into a man-in-the-middle attack, where the   miscreants can insert themselves into the traffic path or divert the   traffic path and violate the confidentiality of user data.2.4.1.2.  Offline Cryptographic Attacks   If any cryptographic mechanism was used to provide for data integrity   and confidentiality, an offline cryptographic attack could   potentially compromise the data.  The traffic would need to be   captured either by eavesdropping on the network or by being able to   divert traffic to a malicious user.  Note that by using   cryptographically protected routing information, the latter would   require the cryptographic key to already be compromised anyway, so   this attack is only feasible if a device was able to eavesdrop and   capture the cryptographically protected routing information.2.4.1.3.  Replay Attacks   For a replay attack to be successful, the routing control plane   traffic would need to first be captured either on-path or diverted to   an attacker to later be replayed to the intended recipient.   Additionally, since many of these protocols include replay protection   mechanisms, these would also need to be subverted, if applicable.2.4.1.4.  Message Insertion/Deletion/Modification   Routing control plane traffic can be manipulated by someone in   control of intermediate hosts.  In addition, traffic can be injected   by forging IP addresses, where a remote router sends out packets that   appear to come from another, trusted router.  If enough traffic is   injected to be processed by limited memory routers, it can cause a   DoS attack.2.4.1.5.  Man-In-The-Middle   A man-in-the-middle attack attacks the identity of a communicating   peer rather than the data stream itself.  The attacker intercepts   traffic that is sent from one routing peer to the other and   communicates on behalf of one of the peers.  This can lead to a   diversion of the user traffic to either an unauthorized receivingKaeo                         Informational                     [Page 19]

RFC 4778                    OPSEC Practices                 January 2007   party or cause legitimate traffic to never reach its intended   destination.2.4.2.  Security Practices   Securing the routing control plane takes many features, which are   generally deployed as a system.  Message Digest 5 (MD5)   authentication is used by some ISPs to validate the sending peer and   to ensure that the data in transit has not been altered.  Some ISPs   only deploy MD5 authentication at the customers' request.  Additional   sanity checks to ensure with reasonable certainty that the received   routing update was originated by a valid routing peer include route   filters and the Generalized TTL Security Mechanism (GTSM) feature   [RFC3682] (sometimes also referred to as the TTL-Hack).  The GTSM   feature is used for protocols such as the Border Gateway Protocol   (BGP), and makes use of a packet's Time To Live (TTL) field (IPv4) or   Hop Limit (IPv6) to protect communicating peers.  If GTSM is used, it   is typically deployed only in limited scenarios between internal BGP   peers due to lack of consistent support between vendor products and   operating system versions.   Packet filters are used to limit which systems can appear as a valid   peer, while route filters are used to limit which routes are believed   to be from a valid peer.  In the case of BGP routing, a variety of   policies are deployed to limit the propagation of invalid routing   information.  These include: incoming and outgoing prefix filters for   BGP customers, incoming and outgoing prefix filters for peers and   upstream neighbors, incoming AS-PATH filter for BGP customers,   outgoing AS-PATH filter towards peers and upstream neighbors, route   dampening and rejecting selected attributes and communities.   Consistency between these policies varies greatly and there is a   definite distinction whether the other end is an end-site vs an   internal peer vs another big ISP or customer.  Mostly ISPs do   prefix-filter their end-site customers, but due to the operational   constraints of maintaining large prefix filter lists, many ISPs are   starting to depend on BGP AS-PATH filters to/from their peers and   upstream neighbors.   In cases where prefix lists are not used, operators often define a   maximum prefix limit per peer to prevent misconfiguration (e.g.,   unintentional de-aggregation or neighbor routing policy   mis-configuration) or overload attacks.  ISPs need to coordinate with   each other what the expected prefix exchange is, and increase this   number by some sane amount.  It is important for ISPs to pad the   max-prefix number enough to allow for valid swings in routing   announcements, preventing an unintentional shut down of the BGP   session.  Individual implementation amongst ISPs are unique, and   depending on equipment supplier(s), different implementation optionsKaeo                         Informational                     [Page 20]

RFC 4778                    OPSEC Practices                 January 2007   are available.  Most equipment vendors offer implementation options   ranging from just logging excessive prefixes being received, to   automatically shutting down the session.  If the option of   reestablishing a session after some pre-configured idle timeout has   been reached is available, it should be understood that automatically   reestablishing the session may potentially introduce instability   continuously into the overall routing table if a policy   mis-configuration on the adjacent neighbor is causing the condition.   If a serious mis-configuration on a peering neighbor has occurred,   then automatically shutting down the session and leaving it shut down   until being manually cleared, is sometimes best and allows for   operator intervention to correct as needed.   Some large ISPs require that routes be registered in an Internet   Routing Registry (IRR), which can then be part of the Routing Assets   Database (RADb) - a public registry of routing information for   networks in the Internet that can be used to generate filter lists.   Some ISPs, especially in Europe, require registered routes before   agreeing to become an eBGP peer with someone.   Many ISPs also do not propagate interface IP addresses to further   reduce attack vectors on routers and connected customers.2.4.3.  Security Services   o  User Authentication - Not applicable.   o  User Authorization - Not applicable.   o  Data Origin Authentication - By using MD5 authentication and/or      the TTL-hack, a routing peer can be reasonably certain that      traffic originated from a valid peer.   o  Access Control - Route filters, AS-PATH filters, and prefix limits      are used to control access to specific parts of the network.   o  Data Integrity - By using MD5 authentication, a peer can be      reasonably certain that the data has not been modified in transit,      but there is no mechanism to prove the validity of the routing      information itself.   o  Data Confidentiality - Not implemented.   o  Auditing / Logging - Filter exceptions are logged.Kaeo                         Informational                     [Page 21]

RFC 4778                    OPSEC Practices                 January 2007   o  DoS Mitigation - Many DoS attacks are mitigated using a      combination of techniques including: MD5 authentication, the GTSM      feature, filtering routing advertisements to bogons, and filtering      routing advertisements to one's own network.2.4.4.  Additional Considerations   So far the primary concern to secure the routing control plane has   been to validate the sending peer and to ensure that the data in   transit has not been altered.  Although MD5 routing protocol   extensions have been implemented, which can provide both services,   they are not consistently deployed amongst ISPs.  Two major   deployment concerns have been implementation issues, where both   software bugs and the lack of graceful re-keying options have caused   significant network down times.  Also, some ISPs express concern that   deploying MD5 authentication will itself be a worse DoS attack victim   and prefer to use a combination of other risk mitigation mechanisms   such as GTSM (for BGP) and route filters.  An issue with GTSM is that   it is not supported on all devices across different vendors'   products.   IPsec is not deployed since the operational management aspects of   ensuring interoperability and reliable configurations is too complex   and time consuming to be operationally viable.  There is also limited   concern to the confidentiality of the routing information.  The   integrity and validity of the updates are of much greater concern.   There is concern for manual or automated actions, which introduce new   routes and can affect the entire routing domain.2.5.  Software Upgrades and Configuration Integrity/Validation   Software upgrades and configuration changes are usually performed as   part of either in-band or OOB management functions.  However, there   are additional considerations to be taken into account, which are   enumerated in this section.2.5.1.  Threats/Attacks   Attacks performed on system software and configurations can be both   from passive or active sources.  Passive attacks are possible if   someone has the capability to intercept data between the network   infrastructure device and the system which is downloading or   uploading the software or configuration information.  This can be   accomplished if a single infrastructure device is somehow compromised   and can act as a network sniffer, or if it is possible to insert a   new device that acts as a network sniffer.Kaeo                         Informational                     [Page 22]

RFC 4778                    OPSEC Practices                 January 2007   Active attacks are possible for both on-path and off-path scenarios.   For on-path active attacks, the situation is the same as for a   passive attack, where either a device has to already be compromised   or a device can be inserted into the path.  For off-path active   attacks, the attacks are generally limited to message insertion or   modification where the attacker may wish to load illegal software or   configuration files to an infrastructure device.   Note that similar issues are relevant when software updates are   downloaded from a vendor site to an ISPs network management system   that is responsible for software updates and/or configuration   information.2.5.1.1.  Confidentiality Violations   Confidentiality violations can occur when a miscreant intercepts any   of the software image or configuration information.  The software   image may give an indication of exploits which the device is   vulnerable to while the configuration information can inadvertently   lead attackers to identify critical infrastructure IP addresses and   passwords.2.5.1.2.  Offline Cryptographic Attacks   If any cryptographic mechanism was used to provide for data integrity   and confidentiality, an offline cryptographic attack could   potentially compromise the data.  The traffic would need to be   captured either by eavesdropping on the communication path or by   being able to divert traffic to a malicious user.2.5.1.3.  Replay Attacks   For a replay attack to be successful, the software image or   configuration file would need to first be captured either on-path or   diverted to an attacker to later be replayed to the intended   recipient.  Additionally, since many protocols do have replay   protection capabilities, these would have to be subverted as well in   applicable situations.2.5.1.4.  Message Insertion/Deletion/Modification   Software images and configuration files can be manipulated by someone   in control of intermediate hosts.  By forging an IP address and   impersonating a valid host which can download software images or   configuration files, invalid files can be downloaded to an   infrastructure device.  This can also be the case from trusted   vendors who may unbeknownst to them have compromised trusted hosts.   An invalid software image or configuration file can cause a device toKaeo                         Informational                     [Page 23]

RFC 4778                    OPSEC Practices                 January 2007   hang and become inoperable.  Spoofed configuration files can be hard   to detect, especially when the only added command is to allow a   miscreant access to that device by entering a filter allowing a   specific host access and configuring a local username/password   database entry for authentication to that device.2.5.1.5.  Man-In-The-Middle   A man-in-the-middle attack attacks the identity of a communicating   peer rather than the data stream itself.  The attacker intercepts   traffic that is sent between the infrastructure device and the host   used to upload/download the system image or configuration file.   He/she can then act on behalf of one or both of these systems.   If an attacker obtained a copy of the software image being deployed,   he could potentially exploit a known vulnerability and gain access to   the system.  From a captured configuration file, he could obtain   confidential network topology information, or even more damaging   information, if any of the passwords in the configuration file were   not encrypted.2.5.2.  Security Practices   Images and configurations are stored on specific hosts that have   limited access.  All access and activity relating to these hosts are   authenticated and logged via AAA services.  When uploaded/downloading   any system software or configuration files, either TFTP, FTP, or SCP   can be used.  Where possible, SCP is used to secure the data transfer   and FTP is generally never used.  All SCP access is username/password   authenticated but since this requires an interactive shell, most ISPs   will use shared key authentication to avoid the interactive shell.   While TFTP access does not have any security measures, it is still   widely used, especially in OOB management scenarios.  Some ISPs   implement IP-based restriction on the TFTP server, while some custom   written TFTP servers will support MAC-based authentication.  The   MAC-based authentication is more common when using TFTP to bootstrap   routers remotely.   In most environments, scripts are used for maintaining the images and   configurations of a large number of routers.  To ensure the integrity   of the configurations, every hour the configuration files are polled   and compared to the previously polled version to find discrepancies.   In at least one environment these, tools are Kerberized to take   advantage of automated authentication (not confidentiality).   'Rancid' is one popular publicly available tool for detecting   configuration and system changes.Kaeo                         Informational                     [Page 24]

RFC 4778                    OPSEC Practices                 January 2007   Filters are used to limit access to uploading/downloading   configuration files and system images to specific IP addresses and   protocols.   The software images perform Cyclic Redundancy Checks (CRC) and the   system binaries use the MD5 algorithm to validate integrity.  Many   ISPs expressed interest in having software image integrity validation   based on the MD5 algorithm for enhanced security.   In all configuration files, most passwords are stored in an encrypted   format.  Note that the encryption techniques used in varying products   can vary and that some weaker encryption schemes may be subject to   off-line dictionary attacks.  This includes passwords for user   authentication, MD5-authentication shared secrets, AAA server shared   secrets, NTP shared secrets, etc.  For older software that may not   support this functionality, configuration files may contain some   passwords in readable format.  Most ISPs mitigate any risk of   password compromise by either storing these configuration files   without the password lines or by requiring authenticated and   authorized access to the configuration files that are stored on   protected OOB management devices.   Automated security validation is performed on infrastructure devices   using Network Mapping (Nmap) and Nessus to ensure valid configuration   against many of the well-known attacks.2.5.3.  Security Services   o  User Authentication - All users are authenticated before being      able to download/upload any system images or configuration files.   o  User Authorization - All authenticated users are granted specific      privileges to download or upload system images and/or      configuration files.   o  Data Origin Authentication - Filters are used to limit access to      uploading/downloading configuration files and system images to      specific IP addresses.   o  Access Control - Filters are used to limit access to uploading/      downloading configuration files and system images to specific IP      addresses and protocols.   o  Data Integrity - All systems use either a CRC-check or MD5      authentication to ensure data integrity.  Also, tools such as      rancid are used to automatically detect configuration changes.Kaeo                         Informational                     [Page 25]

RFC 4778                    OPSEC Practices                 January 2007   o  Data Confidentiality - If the SCP protocol is used then there is      confidentiality of the downloaded/uploaded configuration files and      system images.   o  Auditing/Logging - All access and activity relating to      downloading/uploading system images and configuration files are      logged via AAA services and filter exception rules.   o  DoS Mitigation - A combination of filtering and CRC-check/      MD5-based integrity checks are used to mitigate the risks of DoS      attacks.  If the software updates and configuration changes are      performed via an OOB management system, this is also added      protection.2.5.4.  Additional Considerations   Where the MD5 algorithm is not used to perform data-integrity   checking of software images and configuration files, ISPs have   expressed an interest in having this functionality.  IPsec is   considered too cumbersome and operationally difficult to use for data   integrity and confidentiality.2.6.  Logging Considerations   Although logging is part of all the previous sections, it is   important enough to be covered as a separate item.  The main issues   revolve around what gets logged, how long are logs kept, and what   mechanisms are used to secure the logged information while it is in   transit and while it is stored.2.6.1.  Threats/Attacks   Attacks on the logged data can be both from passive or active   sources.  Passive attacks are possible if someone has the capability   to intercept data between the recipient logging server and the device   from which the logged data originated.  This can be accomplished if a   single infrastructure device is somehow compromised and can act as a   network sniffer, or if it is possible to insert a new device that   acts as a network sniffer.   Active attacks are possible for both on-path and off-path scenarios.   For on-path active attacks, the situation is the same as for a   passive attack, where either a device has to already be compromised,   or a device can be inserted into the path.  For off-path active   attacks, the attacks are generally limited to message insertion or   modification that can alter the logged data to keep any compromise   from being detected, or to destroy any evidence that could be used   for criminal prosecution.Kaeo                         Informational                     [Page 26]

RFC 4778                    OPSEC Practices                 January 20072.6.1.1.  Confidentiality Violations   Confidentiality violations can occur when a miscreant intercepts any   of the logging data that is in transit on the network.  This could   lead to privacy violations if some of the logged data has not been   sanitized to disallow any data that could be a violation of privacy   to be included in the logged data.2.6.1.2.  Offline Cryptographic Attacks   If any cryptographic mechanism was used to provide for data integrity   and confidentiality, an offline cryptographic attack could   potentially compromise the data.  The traffic would need to be   captured either by eavesdropping on the network or by being able to   divert traffic to a malicious user.2.6.1.3.  Replay Attacks   For a replay attack to be successful, the logging data would need to   first be captured either on-path or diverted to an attacker and later   replayed to the recipient.2.6.1.4.  Message Insertion/Deletion/Modification   Logging data could be injected, deleted, or modified by someone in   control of intermediate hosts.  Logging data can also be injected by   forging packets from either legitimate or illegitimate IP addresses.2.6.1.5.  Man-In-The-Middle   A man-in-the-middle attack attacks the identity of a communicating   peer rather than the data stream itself.  The attacker intercepts   traffic that is sent between the infrastructure device and the   logging server or traffic sent between the logging server and the   database that is used to archive the logged data.  Any unauthorized   access to logging information could lead to the knowledge of private   and proprietary network topology information, which could be used to   compromise portions of the network.  An additional concern is having   access to logging information, which could be deleted or modified so   as to cover any traces of a security breach.2.6.2.  Security Practices   When it comes to filtering, logging is mostly performed on an   exception auditing basis (i.e., traffic that is NOT allowed is   logged).  This is to assure that the logging servers are not   overwhelmed with data, which would render most logs unusable.   Typically the data logged will contain the source and destination IPKaeo                         Informational                     [Page 27]

RFC 4778                    OPSEC Practices                 January 2007   addresses and layer 4 port numbers as well as a timestamp.  The   syslog protocol is used to transfer the logged data between the   infrastructure device to the syslog server.  Many ISPs use the OOB   management network to transfer syslog data since there is virtually   no security performed between the syslog server and the device.  All   ISPs have multiple syslog servers - some ISPs choose to use separate   syslog servers for varying infrastructure devices (i.e., one syslog   server for backbone routers, one syslog server for customer edge   routers, etc.)   The timestamp is derived from NTP, which is generally configured as a   flat hierarchy at stratum1 and stratum2 to have less configuration   and less maintenance.  Consistency of configuration and redundancy is   the primary goal.  Each router is configured with several stratum1   server sources, which are chosen to ensure that proper NTP time is   available, even in the event of varying network outages.   In addition to logging filtering exceptions, the following is   typically logged: routing protocol state changes, all device access   (regardless of authentication success or failure), all commands   issued to a device, all configuration changes, and all router events   (boot-up/flaps).   The main function of any of these log messages is to see what the   device is doing as well as to try and ascertain what certain   malicious attackers are trying to do.  Since syslog is an unreliable   protocol, when routers boot or lose adjacencies, not all messages   will get delivered to the remote syslog server.  Some vendors may   implement syslog buffering (e.g., buffer the messages until you have   a route to the syslog destination), but this is not standard.   Therefore, operators often have to look at local syslog information   on a device (which typically has very little memory allocated to it)   to make up for the fact that the server-based syslog files can be   incomplete.  Some ISPs also put in passive devices to see routing   updates and withdrawals and do not rely solely on the device for log   files.  This provides a backup mechanism to see what is going on in   the network in the event that a device may 'forget' to do syslog if   the CPU is busy.   The logs from the various syslog server devices are generally   transferred into databases at a set interval that can be anywhere   from every 10 minutes to every hour.  One ISP uses Rsync to push the   data into a database, and then the information is sorted manually by   someone SSH'ing to that database.Kaeo                         Informational                     [Page 28]

RFC 4778                    OPSEC Practices                 January 20072.6.3.  Security Services   o  User Authentication - Not applicable.   o  User Authorization - Not applicable.   o  Data Origin Authentication - Not implemented.   o  Access Control - Filtering on logging host and server IP address      to ensure that syslog information only goes to specific syslog      hosts.   o  Data Integrity - Not implemented.   o  Data Confidentiality - Not implemented.   o  Auditing/Logging - This entire section deals with logging.   o  DoS Mitigation - An OOB management system is used and sometimes      different syslog servers are used for logging information from      varying equipment.  Exception logging tries to keep information to      a minimum.2.6.4.  Additional Considerations   There is no security with syslog and ISPs are fully cognizant of   this.  IPsec is considered too operationally expensive and cumbersome   to deploy.  Syslog-ng and stunnel are being looked at for providing   better authenticated and integrity-protected solutions.  Mechanisms   to prevent unauthorized personnel from tampering with logs is   constrained to auditing who has access to the logging servers and   files.   ISPs expressed requirements for more than just UDP syslog.   Additionally, they would like more granular and flexible facilities   and priorities, i.e., specific logs to specific servers.  Also, a   common format for reporting standard events so that modifying parsers   after each upgrade of a vendor device or software is not necessary.2.7.  Filtering Considerations   Although filtering has been covered under many of the previous   sections, this section will provide some more insights to the   filtering considerations that are currently being taken into account.   Filtering is now being categorized into three specific areas: data   plane, management plane, and routing control plane.Kaeo                         Informational                     [Page 29]

RFC 4778                    OPSEC Practices                 January 20072.7.1.  Data Plane Filtering   Data plane filters control the traffic that traverses through a   device and affects transit traffic.  Most ISPs deploy these kinds of   filters at customer facing edge devices to mitigate spoofing attacks   usingBCP38 andBCP84 guidelines.2.7.2.  Management Plane Filtering   Management filters control the traffic to and from a device.  All of   the protocols that are used for device management fall under this   category and include: SSH, Telnet, SNMP, NTP, HTTP, DNS, TFTP, FTP,   SCP, and Syslog.  This type of traffic is often filtered per   interface and is based on any combination of protocol, source and   destination IP address, and source and destination port number.  Some   devices support functionality to apply management filters to the   device rather than to the specific interfaces (e.g., receive ACL or   loopback interface ACL), which is gaining wider acceptance.  Note   that logging the filtering rules can today place a burden on many   systems and more granularity is often required to more specifically   log the required exceptions.   Any services that are not specifically used are turned off.   IPv6 networks require the use of specific ICMP messages for proper   protocol operation.  Therefore, ICMP cannot be completely filtered to   and from a device.  Instead, granular ICMPv6 filtering is always   deployed to allow for specific ICMPv6 types to be sourced or destined   to a network device.  A good guideline for IPv6 filtering is in the   Recommendations for Filtering ICMPv6 Messages in Firewalls [ICMPv6].2.7.3.  Routing Control Plane Filtering   Routing filters are used to control the flow of routing information.   In IPv6 networks, some providers are liberal in accepting /48s due to   the still unresolved multihoming issues, while others filter at   allocation boundaries, which are typically at /32.  Any announcement   received that is longer than a /48 for IPv6 routing and a /24 for   IPv4 routing is filtered out of eBGP.  Note that this is for   non-customer traffic.  Most ISPs will accept any agreed upon prefix   length from its customer(s).2.8.  Denial-of-Service Tracking/Tracing   Denial-of-Service attacks are an ever-increasing problem and require   vast amounts of resources to combat effectively.  Some large ISPs do   not concern themselves with attack streams that are less than 1G in   bandwidth - this is on the larger pipes where 1G is essentially lessKaeo                         Informational                     [Page 30]

RFC 4778                    OPSEC Practices                 January 2007   than 5% of an offered load.  This is largely due to the large amounts   of DoS traffic, which continually requires investigation and   mitigation.  At last count, the number of hosts making up large   distributed DoS botnets exceeded 1 million hosts.   New techniques are continually evolving to automate the process of   detecting DoS sources and mitigating any adverse effects as quickly   as possible.  At this time, ISPs are using a variety of mitigation   techniques including: sinkhole routing, black hole triggered routing,   uRPF, rate limiting, and specific control plane traffic enhancements.   Each of these techniques will be detailed below.2.8.1.  Sinkhole Routing   Sinkhole routing refers to injecting a more specific route for any   known attack traffic, which will ensure that the malicious traffic is   redirected to a valid device or specific system where it can be   analyzed.2.8.2.  Black Hole Triggered Routing   Black hole triggered routing (also referred to as Remote Triggered   Black Hole Filtering) is a technique where the BGP routing protocol   is used to propagate routes which in turn redirects attack traffic to   the null interface where it is effectively dropped.  This technique   is often used in large routing infrastructures since BGP can   propagate the information in a fast, effective manner, as opposed to   using any packet-based filtering techniques on hundreds or thousands   of routers (refer to the following NANOG presentation for a more   complete descriptionhttp://www.nanog.org/mtg-0402/pdf/morrow.pdf).   Note that this black-holing technique may actually fulfill the goal   of the attacker if the goal was to instigate black-holing traffic   that appeared to come from a certain site.  On the other hand, this   black hole technique can decrease the collateral damage caused by an   overly large attack aimed at something other than critical services.2.8.3.  Unicast Reverse Path Forwarding   Unicast Reverse Path Forwarding (uRPF) is a mechanism for validating   whether or not an incoming packet has a legitimate source address.   It has two modes: strict mode and loose mode.  In strict mode, uRPF   checks whether the incoming packet has a source address that matches   a prefix in the routing table, and whether the interface expects to   receive a packet with this source address prefix.  If the incoming   packet fails the unicast RPF check, the packet is not accepted on theKaeo                         Informational                     [Page 31]

RFC 4778                    OPSEC Practices                 January 2007   incoming interface.  Loose mode uRPF is not as specific and the   incoming packet is accepted if there is any route in the routing   table for the source address.   WhileBCP84 [RFC3704] and a study on uRPF experiences [BCP84-URPF]   detail how asymmetry, i.e., multiple routes to the source of a   packet, does not preclude applying feasible paths strict uRPF, it is   generally not used on interfaces that are likely to have routing   asymmetry.  Usually for the larger ISPs, uRPF is placed at the   customer edge of a network.2.8.4.  Rate Limiting   Rate limiting refers to allocating a specific amount of bandwidth or   packets per second to specific traffic types.  This technique is   widely used to mitigate well-known protocol attacks such as the   TCP-SYN attack, where a large number of resources get allocated for   spoofed TCP traffic.  Although this technique does not stop an   attack, it can sometimes lessen the damage and impact on a specific   service.  However, it can also make the impact of a DoS attack much   worse if the rate limiting is impacting (i.e., discarding) more   legitimate traffic.2.8.5.  Specific Control Plane Traffic Enhancements   Some ISPs are starting to use capabilities that are available from   some vendors to simplify the filtering and rate limiting of control   traffic.  Control traffic here refers to the routing control plane   and management plane traffic that requires CPU cycles.  A DoS attack   against any control plane traffic can therefore be much more damaging   to a critical device than other types of traffic.  No consistent   deployment of this capability was found at the time of this writing.3.  Security Considerations   This entire document deals with current security practices in large   ISP environments.  It lists specific practices used in today's   environments and as such, does not in itself pose any security risk.4.  Acknowledgments   The editor gratefully acknowledges the contributions of: George   Jones, who has been instrumental in providing guidance and direction   for this document, and the insightful comments from Ross Callon, Ron   Bonica, Ryan Mcdowell, Gaurab Upadhaya, Warren Kumari, Pekka Savola,   Fernando Gont, Chris Morrow, Ted Seely, Donald Smith, and the   numerous ISP operators who supplied the information that is depicted   in this document.Kaeo                         Informational                     [Page 32]

RFC 4778                    OPSEC Practices                 January 20075.  References5.1.  Normative References   [RFC2827]     Ferguson, P. and D. Senie, "Network Ingress Filtering:                 Defeating Denial of Service Attacks which employ IP                 Source Address Spoofing",BCP 38,RFC 2827, May 2000.   [RFC2828]     Shirey, R., "Internet Security Glossary",RFC 2828,                 May 2000.   [RFC3552]     Rescorla, E. and B. Korver, "Guidelines for Writing RFC                 Text on Security Considerations",BCP 72,RFC 3552,                 July 2003.   [RFC3682]     Gill, V., Heasley, J., and D. Meyer, "The Generalized                 TTL Security Mechanism (GTSM)",RFC 3682,                 February 2004.   [RFC3704]     Baker, F. and P. Savola, "Ingress Filtering for                 Multihomed Networks",BCP 84,RFC 3704, March 2004.   [RFC3882]     Turk, D., "Configuring BGP to Block Denial-of-Service                 Attacks",RFC 3882, September 2004.5.2.  Informational References   [BCP84-URPF]  Savola, P.,"Experiences from Using Unicast RPF", Work                 in Progress, November 2006.   [ICMPv6]      Davies, E. and J. Mohacsi, "Recommendations for                 Filtering ICMPv6 Messages in Firewalls", Work                 in Progress, July 2006.   [RTGWG]       Savola, P., "Backbone Infrastructure Attacks and                 Protections", Work in Progress, July 2006.Kaeo                         Informational                     [Page 33]

RFC 4778                    OPSEC Practices                 January 2007Appendix A.  Protocol Specific Attacks   This section will list many of the traditional protocol-based attacks   that have been observed over the years to cause malformed packets   and/or exploit protocol deficiencies.  Note that they all exploit   vulnerabilities in the actual protocol itself and often, additional   authentication and auditing mechanisms are now used to detect and   mitigate the impact of these attacks.  The list is not exhaustive,   but is a fraction of the representation of what types of attacks are   possible for varying protocols.A.1.  Layer 2 Attacks   o  ARP FloodingA.2.  IPv4 Protocol-Based Attacks   o  IP Addresses, either source or destination, can be spoofed which      in turn can circumvent established filtering rules.   o  IP Source Route Option can allows attackers to establish stealth      TCP connections.   o  IP Record Route Option can disclose information about the topology      of the network.   o  IP header that is too long or too short can cause DoS attacks to      devices.   o  IP Timestamp Option can leak information that can be used to      discern network behavior.   o  Fragmentation attacks which can vary widely - more detailed      information can be found athttp://www-src.lip6.fr/homepages/Fabrice.Legond-Aubry/www.ouah.org/fragma.html.   o  IP ToS field (or the Differentiated Services (DSCP) field) can be      used to reroute or reclassify traffic based on specified      precedence.   o  IP checksum field has been used for scanning purposes, for example      when some firewalls did not check the checksum and allowed an      attacker to differentiate when the response came from an end-      system, and when from a firewall.   o  IP TTL field can be used to bypass certain network-based intrusion      detection systems and to map network behavior.Kaeo                         Informational                     [Page 34]

RFC 4778                    OPSEC Practices                 January 2007A.2.1.  Higher Layer Protocol Attacks   The following lists additional attacks, but does not explicitly   numerate them in detail.  It is for informational purposes only.   o  IGMP oversized packet   o  ICMP Source Quench   o  ICMP Mask Request   o  ICMP Large Packet (> 1472)   o  ICMP Oversized packet (>65536)   o  ICMP Flood   o  ICMP Broadcast w/ Spoofed Source (Smurf Attack)   o  ICMP Error Packet Flood   o  ICMP Spoofed Unreachable   o  TCP Packet without Flag   o  TCP Oversized Packet   o  TCP FIN bit with no ACK bit   o  TCP Packet with URG/OOB flag (Nuke Attack)   o  SYN Fragments   o  SYN Flood   o  SYN with IP Spoofing (Land Attack)   o  SYN and FIN bits set   o  TCP port scan attack   o  UDP spoofed broadcast echo (Fraggle Attack)   o  UDP attack on diagnostic ports (Pepsi Attack)Kaeo                         Informational                     [Page 35]

RFC 4778                    OPSEC Practices                 January 2007A.3.  IPv6 Attacks   Any of the above-mentioned IPv4 attacks could be used in IPv6   networks with the exception of any fragmentation and broadcast   traffic, which operate differently in IPv6.  Note that all of these   attacks are based on either spoofing or misusing any part of the   protocol field(s).   Today, IPv6-enabled hosts are starting to be used to create IPv6   tunnels, which can effectively hide botnet and other malicious   traffic if firewalls and network flow collection tools are not   capable of detecting this traffic.  The security measures used for   protecting IPv6 infrastructures should be the same as in IPv4   networks, but with additional considerations for IPv6 network   operations, which may be different from IPv4.Author's Address   Merike Kaeo   Double Shot Security, Inc.   3518 Fremont Avenue North #363   Seattle, WA  98103   U.S.A.   Phone: +1 310 866 0165   EMail: merike@doubleshotsecurity.comKaeo                         Informational                     [Page 36]

RFC 4778                    OPSEC Practices                 January 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Kaeo                         Informational                     [Page 37]