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Network Working Group                                         P. MarquesRequest for Comments: 5575                                 Cisco SystemsCategory: Standards Track                                       N. Sheth                                                        Juniper Networks                                                               R. Raszuk                                                           Cisco Systems                                                               B. Greene                                                        Juniper Networks                                                                J. Mauch                                                             NTT America                                                            D. McPherson                                                          Arbor Networks                                                             August 2009Dissemination of Flow Specification RulesAbstract   This document defines a new Border Gateway Protocol Network Layer   Reachability Information (BGP NLRI) encoding format that can be used   to distribute traffic flow specifications.  This allows the routing   system to propagate information regarding more specific components of   the traffic aggregate defined by an IP destination prefix.   Additionally, it defines two applications of that encoding format:   one that can be used to automate inter-domain coordination of traffic   filtering, such as what is required in order to mitigate   (distributed) denial-of-service attacks, and a second application to   provide traffic filtering in the context of a BGP/MPLS VPN service.   The information is carried via the BGP, thereby reusing protocol   algorithms, operational experience, and administrative processes such   as inter-provider peering agreements.Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Marques, et al.             Standards Track                     [Page 1]

RFC 5575                   Flow Specification                August 2009Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.Table of Contents1. Introduction ....................................................32. Definitions of Terms Used in This Memo ..........................53. Flow Specifications .............................................54. Dissemination of Information ....................................65. Traffic Filtering ..............................................125.1. Order of Traffic Filtering Rules ..........................136. Validation Procedure ...........................................147. Traffic Filtering Actions ......................................158. Traffic Filtering in BGP/MPLS VPN Networks .....................179. Monitoring .....................................................1810. Security Considerations .......................................1811. IANA Considerations ...........................................1912. Acknowledgments ...............................................2013. Normative References ..........................................21Marques, et al.             Standards Track                     [Page 2]

RFC 5575                   Flow Specification                August 20091.  Introduction   Modern IP routers contain both the capability to forward traffic   according to IP prefixes as well as to classify, shape, rate limit,   filter, or redirect packets based on administratively defined   policies.   These traffic policy mechanisms allow the router to define match   rules that operate on multiple fields of the packet header.  Actions   such as the ones described above can be associated with each rule.   The n-tuple consisting of the matching criteria defines an aggregate   traffic flow specification.  The matching criteria can include   elements such as source and destination address prefixes, IP   protocol, and transport protocol port numbers.   This document defines a general procedure to encode flow   specification rules for aggregated traffic flows so that they can be   distributed as a BGP [RFC4271] NLRI.  Additionally, we define the   required mechanisms to utilize this definition to the problem of   immediate concern to the authors: intra- and inter-provider   distribution of traffic filtering rules to filter (distributed)   denial-of-service (DoS) attacks.   By expanding routing information with flow specifications, the   routing system can take advantage of the ACL (Access Control List) or   firewall capabilities in the router's forwarding path.  Flow   specifications can be seen as more specific routing entries to a   unicast prefix and are expected to depend upon the existing unicast   data information.   A flow specification received from an external autonomous system will   need to be validated against unicast routing before being accepted.   If the aggregate traffic flow defined by the unicast destination   prefix is forwarded to a given BGP peer, then the local system can   safely install more specific flow rules that may result in different   forwarding behavior, as requested by this system.   The key technology components required to address the class of   problems targeted by this document are:   1.  Efficient point-to-multipoint distribution of control plane       information.   2.  Inter-domain capabilities and routing policy support.   3.  Tight integration with unicast routing, for verification       purposes.Marques, et al.             Standards Track                     [Page 3]

RFC 5575                   Flow Specification                August 2009   Items 1 and 2 have already been addressed using BGP for other types   of control plane information.  Close integration with BGP also makes   it feasible to specify a mechanism to automatically verify flow   information against unicast routing.  These factors are behind the   choice of BGP as the carrier of flow specification information.   As with previous extensions to BGP, this specification makes it   possible to add additional information to Internet routers.  These   are limited in terms of the maximum number of data elements they can   hold as well as the number of events they are able to process in a   given unit of time.  The authors believe that, as with previous   extensions, service providers will be careful to keep information   levels below the maximum capacity of their devices.   It is also expected that, in many initial deployments, flow   specification information will replace existing host length route   advertisements rather than add additional information.   Experience with previous BGP extensions has also shown that the   maximum capacity of BGP speakers has been gradually increased   according to expected loads.  Taking into account Internet unicast   routing as well as additional applications as they gain popularity.   From an operational perspective, the utilization of BGP as the   carrier for this information allows a network service provider to   reuse both internal route distribution infrastructure (e.g., route   reflector or confederation design) and existing external   relationships (e.g., inter-domain BGP sessions to a customer   network).   While it is certainly possible to address this problem using other   mechanisms, the authors believe that this solution offers the   substantial advantage of being an incremental addition to already   deployed mechanisms.   In current deployments, the information distributed by the flow-spec   extension is originated both manually as well as automatically.  The   latter by systems that are able to detect malicious flows.  When   automated systems are used, care should be taken to ensure their   correctness as well as to limit the number and advertisement rate of   flow routes.   This specification defines required protocol extensions to address   most common applications of IPv4 unicast and VPNv4 unicast filtering.   The same mechanism can be reused and new match criteria added to   address similar filtering needs for other BGP address families (for   example, IPv6 unicast).  The authors believe that those would be best   to be addressed in a separate document.Marques, et al.             Standards Track                     [Page 4]

RFC 5575                   Flow Specification                August 20092.  Definitions of Terms Used in This Memo   NLRI - Network Layer Reachability Information   RIB - Routing Information Base   Loc-RIB - Local RIB   AS - Autonomous System number   VRF - Virtual Routing and Forwarding instance   PE - Provider Edge router   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].3.  Flow Specifications   A flow specification is an n-tuple consisting of several matching   criteria that can be applied to IP traffic.  A given IP packet is   said to match the defined flow if it matches all the specified   criteria.   A given flow may be associated with a set of attributes, depending on   the particular application; such attributes may or may not include   reachability information (i.e., NEXT_HOP).  Well-known or AS-specific   community attributes can be used to encode a set of predetermined   actions.   A particular application is identified by a specific (Address Family   Identifier, Subsequent Address Family Identifier (AFI, SAFI)) pair   [RFC4760] and corresponds to a distinct set of RIBs.  Those RIBs   should be treated independently from each other in order to assure   non-interference between distinct applications.   BGP itself treats the NLRI as an opaque key to an entry in its   databases.  Entries that are placed in the Loc-RIB are then   associated with a given set of semantics, which is application   dependent.  This is consistent with existing BGP applications.  For   instance, IP unicast routing (AFI=1, SAFI=1) and IP multicast   reverse-path information (AFI=1, SAFI=2) are handled by BGP without   any particular semantics being associated with them until installed   in the Loc-RIB.Marques, et al.             Standards Track                     [Page 5]

RFC 5575                   Flow Specification                August 2009   Standard BGP policy mechanisms, such as UPDATE filtering by NLRI   prefix and community matching, SHOULD apply to the newly defined   NLRI-type.  Network operators can also control propagation of such   routing updates by enabling or disabling the exchange of a particular   (AFI, SAFI) pair on a given BGP peering session.4.  Dissemination of Information   We define a "Flow Specification" NLRI type that may include several   components such as destination prefix, source prefix, protocol,   ports, etc.  This NLRI is treated as an opaque bit string prefix by   BGP.  Each bit string identifies a key to a database entry with which   a set of attributes can be associated.   This NLRI information is encoded using MP_REACH_NLRI and   MP_UNREACH_NLRI attributes as defined inRFC 4760 [RFC4760].   Whenever the corresponding application does not require Next-Hop   information, this shall be encoded as a 0-octet length Next Hop in   the MP_REACH_NLRI attribute and ignored on receipt.   The NLRI field of the MP_REACH_NLRI and MP_UNREACH_NLRI is encoded as   a 1- or 2-octet NLRI length field followed by a variable-length NLRI   value.  The NLRI length is expressed in octets.                      +------------------------------+                      |    length (0xnn or 0xfn nn)  |                      +------------------------------+                      |    NLRI value  (variable)    |                      +------------------------------+                              flow-spec NLRI   If the NLRI length value is smaller than 240 (0xf0 hex), the length   field can be encoded as a single octet.  Otherwise, it is encoded as   an extended-length 2-octet value in which the most significant nibble   of the first byte is all ones.   In the figure above, values less-than 240 are encoded using two hex   digits (0xnn).  Values above 240 are encoded using 3 hex digits   (0xfnnn).  The highest value that can be represented with this   encoding is 4095.  The value 241 is encoded as 0xf0f1.   The Flow specification NLRI-type consists of several optional   subcomponents.  A specific packet is considered to match the flow   specification when it matches the intersection (AND) of all the   components present in the specification.Marques, et al.             Standards Track                     [Page 6]

RFC 5575                   Flow Specification                August 2009   The following component types are defined:      Type 1 - Destination Prefix         Encoding: <type (1 octet), prefix length (1 octet), prefix>         Defines the destination prefix to match.  Prefixes are encoded         as in BGP UPDATE messages, a length in bits is followed by         enough octets to contain the prefix information.      Type 2 - Source Prefix         Encoding: <type (1 octet), prefix-length (1 octet), prefix>         Defines the source prefix to match.      Type 3 - IP Protocol         Encoding: <type (1 octet), [op, value]+>         Contains a set of {operator, value} pairs that are used to         match the IP protocol value byte in IP packets.         The operator byte is encoded as:                       0   1   2   3   4   5   6   7                     +---+---+---+---+---+---+---+---+                     | e | a |  len  | 0 |lt |gt |eq |                     +---+---+---+---+---+---+---+---+                                Numeric operator         e -   end-of-list bit.  Set in the last {op, value} pair in the               list.         a -   AND bit.  If unset, the previous term is logically ORed               with the current one.  If set, the operation is a logical               AND.  It should be unset in the first operator byte of a               sequence.  The AND operator has higher priority than OR               for the purposes of evaluating logical expressions.         len - The length of the value field for this operand is given               as (1 << len).         lt -  less than comparison between data and value.         gt -  greater than comparison between data and value.Marques, et al.             Standards Track                     [Page 7]

RFC 5575                   Flow Specification                August 2009         eq -  equality between data and value.         The bits lt, gt, and eq can be combined to produce "less or         equal", "greater or equal", and inequality values.      Type 4 - Port         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs that matches source         OR destination TCP/UDP ports.  This list is encoded using the         numeric operand format defined above.  Values are encoded as 1-         or 2-byte quantities.         Port, source port, and destination port components evaluate to         FALSE if the IP protocol field of the packet has a value other         than TCP or UDP, if the packet is fragmented and this is not         the first fragment, or if the system in unable to locate the         transport header.  Different implementations may or may not be         able to decode the transport header in the presence of IP         options or Encapsulating Security Payload (ESP) NULL [RFC4303]         encryption.      Type 5 - Destination port         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs used to match the         destination port of a TCP or UDP packet.  Values are encoded as         1- or 2-byte quantities.      Type 6 - Source port         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs used to match the         source port of a TCP or UDP packet.  Values are encoded as 1-         or 2-byte quantities.      Type 7 - ICMP type         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs used to match the         type field of an ICMP packet.  Values are encoded using a         single byte.Marques, et al.             Standards Track                     [Page 8]

RFC 5575                   Flow Specification                August 2009         The ICMP type and code specifiers evaluate to FALSE whenever         the protocol value is not ICMP.      Type 8 - ICMP code         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs used to match the         code field of an ICMP packet.  Values are encoded using a         single byte.      Type 9 - TCP flags         Encoding: <type (1 octet), [op, bitmask]+>         Bitmask values can be encoded as a 1- or 2-byte bitmask.  When         a single byte is specified, it matches byte 13 of the TCP         header [RFC0793], which contains bits 8 though 15 of the 4th         32-bit word.  When a 2-byte encoding is used, it matches bytes         12 and 13 of the TCP header with the data offset field having a         "don't care" value.         As with port specifiers, this component evaluates to FALSE for         packets that are not TCP packets.         This type uses the bitmask operand format, which differs from         the numeric operator format in the lower nibble.                       0   1   2   3   4   5   6   7                     +---+---+---+---+---+---+---+---+                     | e | a |  len  | 0 | 0 |not| m |                     +---+---+---+---+---+---+---+---+         e, a, len -  Most significant nibble: (end-of-list bit, AND                      bit, and length field), as defined for in the                      numeric operator format.         not - NOT bit.  If set, logical negation of operation.         m -   Match bit.  If set, this is a bitwise match operation               defined as "(data & value) == value"; if unset, (data &               value) evaluates to TRUE if any of the bits in the value               mask are set in the data.Marques, et al.             Standards Track                     [Page 9]

RFC 5575                   Flow Specification                August 2009      Type 10 - Packet length         Encoding: <type (1 octet), [op, value]+>         Match on the total IP packet length (excluding Layer 2 but         including IP header).  Values are encoded using 1- or 2-byte         quantities.      Type 11 - DSCP (Diffserv Code Point)         Encoding: <type (1 octet), [op, value]+>         Defines a list of {operation, value} pairs used to match the         6-bit DSCP field [RFC2474].  Values are encoded using a single         byte, where the two most significant bits are zero and the six         least significant bits contain the DSCP value.      Type 12 - Fragment         Encoding: <type (1 octet), [op, bitmask]+>         Uses bitmask operand format defined above.                       0   1   2   3   4   5   6   7                     +---+---+---+---+---+---+---+---+                     |   Reserved    |LF |FF |IsF|DF |                     +---+---+---+---+---+---+---+---+         Bitmask values:         +  Bit 7 - Don't fragment (DF)         +  Bit 6 - Is a fragment (IsF)         +  Bit 5 - First fragment (FF)         +  Bit 4 - Last fragment (LF)   Flow specification components must follow strict type ordering.  A   given component type may or may not be present in the specification,   but if present, it MUST precede any component of higher numeric type   value.   If a given component type within a prefix in unknown, the prefix in   question cannot be used for traffic filtering purposes by the   receiver.  Since a flow specification has the semantics of a logical   AND of all components, if a component is FALSE, by definition it   cannot be applied.  However, for the purposes of BGP routeMarques, et al.             Standards Track                    [Page 10]

RFC 5575                   Flow Specification                August 2009   propagation, this prefix should still be transmitted since BGP route   distribution is independent on NLRI semantics.   The <type, value> encoding is chosen in order to account for future   extensibility.   An example of a flow specification encoding for: "all packets to   10.0.1/24 and TCP port 25".   +------------------+----------+----------+   | destination      | proto    | port     |   +------------------+----------+----------+   | 0x01 18 0a 00 01 | 03 81 06 | 04 81 19 |   +------------------+----------+----------+   Decode for protocol:   +-------+----------+------------------------------+   | Value |          |                              |   +-------+----------+------------------------------+   |  0x03 | type     |                              |   |  0x81 | operator | end-of-list, value size=1, = |   |  0x06 | value    |                              |   +-------+----------+------------------------------+   An example of a flow specification encoding for: "all packets to   10.0.1/24 from 192/8 and port {range [137, 139] or 8080}".   +------------------+----------+-------------------------+   | destination      | source   | port                    |   +------------------+----------+-------------------------+   | 0x01 18 0a 01 01 | 02 08 c0 | 04 03 89 45 8b 91 1f 90 |   +------------------+----------+-------------------------+   Decode for port:   +--------+----------+------------------------------+   |  Value |          |                              |   +--------+----------+------------------------------+   |   0x04 | type     |                              |   |   0x03 | operator | size=1, >=                   |   |   0x89 | value    | 137                          |   |   0x45 | operator | &, value size=1, <=          |   |   0x8b | value    | 139                          |   |   0x91 | operator | end-of-list, value-size=2, = |   | 0x1f90 | value    | 8080                         |   +--------+----------+------------------------------+Marques, et al.             Standards Track                    [Page 11]

RFC 5575                   Flow Specification                August 2009   This constitutes an NLRI with an NLRI length of 16 octets.   Implementations wishing to exchange flow specification rules MUST use   BGP's Capability Advertisement facility to exchange the Multiprotocol   Extension Capability Code (Code 1) as defined inRFC 4760 [RFC4760].   The (AFI, SAFI) pair carried in the Multiprotocol Extension   Capability MUST be the same as the one used to identify a particular   application that uses this NLRI-type.5.  Traffic Filtering   Traffic filtering policies have been traditionally considered to be   relatively static.   The popularity of traffic-based, denial-of-service (DoS) attacks,   which often requires the network operator to be able to use traffic   filters for detection and mitigation, brings with it requirements   that are not fully satisfied by existing tools.   Increasingly, DoS mitigation requires coordination among several   service providers in order to be able to identify traffic source(s)   and because the volumes of traffic may be such that they will   otherwise significantly affect the performance of the network.   Several techniques are currently used to control traffic filtering of   DoS attacks.  Among those, one of the most common is to inject   unicast route advertisements corresponding to a destination prefix   being attacked.  One variant of this technique marks such route   advertisements with a community that gets translated into a discard   Next-Hop by the receiving router.  Other variants attract traffic to   a particular node that serves as a deterministic drop point.   Using unicast routing advertisements to distribute traffic filtering   information has the advantage of using the existing infrastructure   and inter-AS communication channels.  This can allow, for instance, a   service provider to accept filtering requests from customers for   address space they own.   There are several drawbacks, however.  An issue that is immediately   apparent is the granularity of filtering control: only destination   prefixes may be specified.  Another area of concern is the fact that   filtering information is intermingled with routing information.   The mechanism defined in this document is designed to address these   limitations.  We use the flow specification NLRI defined above to   convey information about traffic filtering rules for traffic that   should be discarded.Marques, et al.             Standards Track                    [Page 12]

RFC 5575                   Flow Specification                August 2009   This mechanism is primarily designed to allow an upstream autonomous   system to perform inbound filtering in their ingress routers of   traffic that a given downstream AS wishes to drop.   In order to achieve this goal, we define an application-specific NLRI   identifier (AFI=1, SAFI=133) along with specific semantic rules.   BGP routing updates containing this identifier use the flow   specification NLRI encoding to convey particular aggregated flows   that require special treatment.   Flow routing information received via this (AFI, SAFI) pair is   subject to the validation procedure detailed below.5.1.  Order of Traffic Filtering Rules   With traffic filtering rules, more than one rule may match a   particular traffic flow.  Thus, it is necessary to define the order   at which rules get matched and applied to a particular traffic flow.   This ordering function must be such that it must not depend on the   arrival order of the flow specification's rules and must be constant   in the network.   The relative order of two flow specification rules is determined by   comparing their respective components.  The algorithm starts by   comparing the left-most components of the rules.  If the types   differ, the rule with lowest numeric type value has higher precedence   (and thus will match before) than the rule that doesn't contain that   component type.  If the component types are the same, then a type-   specific comparison is performed.   For IP prefix values (IP destination and source prefix) precedence is   given to the lowest IP value of the common prefix length; if the   common prefix is equal, then the most specific prefix has precedence.   For all other component types, unless otherwise specified, the   comparison is performed by comparing the component data as a binary   string using the memcmp() function as defined by the ISO C standard.   For strings of different lengths, the common prefix is compared.  If   equal, the longest string is considered to have higher precedence   than the shorter one.Marques, et al.             Standards Track                    [Page 13]

RFC 5575                   Flow Specification                August 2009   Pseudocode:   flow_rule_cmp (a, b)   {       comp1 = next_component(a);       comp2 = next_component(b);       while (comp1 || comp2) {           // component_type returns infinity on end-of-list           if (component_type(comp1) < component_type(comp2)) {               return A_HAS_PRECEDENCE;           }           if (component_type(comp1) > component_type(comp2)) {               return B_HAS_PRECEDENCE;           }           if (component_type(comp1) == IP_DESTINATION || IP_SOURCE) {               common = MIN(prefix_length(comp1), prefix_length(comp2));               cmp = prefix_compare(comp1, comp2, common);               // not equal, lowest value has precedence               // equal, longest match has precedence           } else {               common =                  MIN(component_length(comp1), component_length(comp2));               cmp = memcmp(data(comp1), data(comp2), common);               // not equal, lowest value has precedence               // equal, longest string has precedence           }       }       return EQUAL;   }6.  Validation Procedure   Flow specifications received from a BGP peer and that are accepted in   the respective Adj-RIB-In are used as input to the route selection   process.  Although the forwarding attributes of two routes for the   same flow specification prefix may be the same, BGP is still required   to perform its path selection algorithm in order to select the   correct set of attributes to advertise.   The first step of the BGP Route Selection procedure (Section 9.1.2 of   [RFC4271]) is to exclude from the selection procedure routes that are   considered non-feasible.  In the context of IP routing information,   this step is used to validate that the NEXT_HOP attribute of a given   route is resolvable.Marques, et al.             Standards Track                    [Page 14]

RFC 5575                   Flow Specification                August 2009   The concept can be extended, in the case of flow specification NLRI,   to allow other validation procedures.   A flow specification NLRI must be validated such that it is   considered feasible if and only if:   a) The originator of the flow specification matches the originator of      the best-match unicast route for the destination prefix embedded      in the flow specification.   b) There are no more specific unicast routes, when compared with the      flow destination prefix, that have been received from a different      neighboring AS than the best-match unicast route, which has been      determined in step a).   By originator of a BGP route, we mean either the BGP originator path   attribute, as used by route reflection, or the transport address of   the BGP peer, if this path attribute is not present.   The underlying concept is that the neighboring AS that advertises the   best unicast route for a destination is allowed to advertise flow-   spec information that conveys a more or equally specific destination   prefix.  Thus, as long as there are no more specific unicast routes,   received from a different neighboring AS, which would be affected by   that filtering rule.   The neighboring AS is the immediate destination of the traffic   described by the flow specification.  If it requests these flows to   be dropped, that request can be honored without concern that it   represents a denial of service in itself.  Supposedly, the traffic is   being dropped by the downstream autonomous system, and there is no   added value in carrying the traffic to it.   BGP implementations MUST also enforce that the AS_PATH attribute of a   route received via the External Border Gateway Protocol (eBGP)   contains the neighboring AS in the left-most position of the AS_PATH   attribute.  While this rule is optional in the BGP specification, it   becomes necessary to enforce it for security reasons.7.  Traffic Filtering Actions   This specification defines a minimum set of filtering actions that it   standardizes as BGP extended community values [RFC4360].  This is not   meant to be an inclusive list of all the possible actions, but only a   subset that can be interpreted consistently across the network.Marques, et al.             Standards Track                    [Page 15]

RFC 5575                   Flow Specification                August 2009   Implementations should provide mechanisms that map an arbitrary BGP   community value (normal or extended) to filtering actions that   require different mappings in different systems in the network.  For   instance, providing packets with a worse-than-best-effort, per-hop   behavior is a functionality that is likely to be implemented   differently in different systems and for which no standard behavior   is currently known.  Rather than attempting to define it here, this   can be accomplished by mapping a user-defined community value to   platform-/network-specific behavior via user configuration.   The default action for a traffic filtering flow specification is to   accept IP traffic that matches that particular rule.      The following extended community values can be used to specify                            particular actions.        +--------+--------------------+--------------------------+        | type   | extended community | encoding                 |        +--------+--------------------+--------------------------+        | 0x8006 | traffic-rate       | 2-byte as#, 4-byte float |        | 0x8007 | traffic-action     | bitmask                  |        | 0x8008 | redirect           | 6-byte Route Target      |        | 0x8009 | traffic-marking    | DSCP value               |        +--------+--------------------+--------------------------+   Traffic-rate:  The traffic-rate extended community is a non-      transitive extended community across the autonomous-system      boundary and uses following extended community encoding:         The first two octets carry the 2-octet id, which can be         assigned from a 2-byte AS number.  When a 4-byte AS number is         locally present, the 2 least significant bytes of such an AS         number can be used.  This value is purely informational and         should not be interpreted by the implementation.         The remaining 4 octets carry the rate information in IEEE         floating point [IEEE.754.1985] format, units being bytes per         second.  A traffic-rate of 0 should result on all traffic for         the particular flow to be discarded.   Traffic-action:  The traffic-action extended community consists of 6      bytes of which only the 2 least significant bits of the 6th byte      (from left to right) are currently defined.                       40  41  42  43  44  45  46  47                     +---+---+---+---+---+---+---+---+                     |        reserved       | S | T |                     +---+---+---+---+---+---+---+---+Marques, et al.             Standards Track                    [Page 16]

RFC 5575                   Flow Specification                August 2009      *  Terminal Action (bit 47): When this bit is set, the traffic         filtering engine will apply any subsequent filtering rules (as         defined by the ordering procedure).  If not set, the evaluation         of the traffic filter stops when this rule is applied.      *  Sample (bit 46): Enables traffic sampling and logging for this         flow specification.   Redirect:  The redirect extended community allows the traffic to be      redirected to a VRF routing instance that lists the specified      route-target in its import policy.  If several local instances      match this criteria, the choice between them is a local matter      (for example, the instance with the lowest Route Distinguisher      value can be elected).  This extended community uses the same      encoding as the Route Target extended community [RFC4360].   Traffic Marking:  The traffic marking extended community instructs a      system to modify the DSCP bits of a transiting IP packet to the      corresponding value.  This extended community is encoded as a      sequence of 5 zero bytes followed by the DSCP value encoded in the      6 least significant bits of 6th byte.8.  Traffic Filtering in BGP/MPLS VPN Networks   Provider-based Layer 3 VPN networks, such as the ones using a BGP/   MPLS IP VPN [RFC4364] control plane, have different traffic filtering   requirements than Internet service providers.   In these environments, the VPN customer network often has traffic   filtering capabilities towards their external network connections   (e.g., firewall facing public network connection).  Less common is   the presence of traffic filtering capabilities between different VPN   attachment sites.  In an any-to-any connectivity model, which is the   default, this means that site-to-site traffic is unfiltered.   In circumstances where a security threat does get propagated inside   the VPN customer network, there may not be readily available   mechanisms to provide mitigation via traffic filter.   This document proposes an additional BGP NLRI type (AFI=1, SAFI=134)   value, which can be used to propagate traffic filtering information   in a BGP/MPLS VPN environment.   The NLRI format for this address family consists of a fixed-length   Route Distinguisher field (8 bytes) followed by a flow specification,   following the encoding defined in this document.  The NLRI length   field shall include both the 8 bytes of the Route Distinguisher as   well as the subsequent flow specification.Marques, et al.             Standards Track                    [Page 17]

RFC 5575                   Flow Specification                August 2009   Propagation of this NLRI is controlled by matching Route Target   extended communities associated with the BGP path advertisement with   the VRF import policy, using the same mechanism as described in "BGP/   MPLS IP VPNs" [RFC4364] .   Flow specification rules received via this NLRI apply only to traffic   that belongs to the VRF(s) in which it is imported.  By default,   traffic received from a remote PE is switched via an MPLS forwarding   decision and is not subject to filtering.   Contrary to the behavior specified for the non-VPN NLRI, flow rules   are accepted by default, when received from remote PE routers.9.  Monitoring   Traffic filtering applications require monitoring and traffic   statistics facilities.  While this is an implementation-specific   choice, implementations SHOULD provide:   o  A mechanism to log the packet header of filtered traffic.   o  A mechanism to count the number of matches for a given flow      specification rule.10.  Security Considerations   Inter-provider routing is based on a web of trust.  Neighboring   autonomous systems are trusted to advertise valid reachability   information.  If this trust model is violated, a neighboring   autonomous system may cause a denial-of-service attack by advertising   reachability information for a given prefix for which it does not   provide service.   As long as traffic filtering rules are restricted to match the   corresponding unicast routing paths for the relevant prefixes, the   security characteristics of this proposal are equivalent to the   existing security properties of BGP unicast routing.   Where it is not the case, this would open the door to further denial-   of-service attacks.   Enabling firewall-like capabilities in routers without centralized   management could make certain failures harder to diagnose.  For   example, it is possible to allow TCP packets to pass between a pair   of addresses but not ICMP packets.  It is also possible to permit   packets smaller than 900 or greater than 1000 bytes to pass between aMarques, et al.             Standards Track                    [Page 18]

RFC 5575                   Flow Specification                August 2009   pair of addresses, but not packets whose length is in the range 900-   1000.  Such behavior may be confusing and these capabilities should   be used with care whether manually configured or coordinated through   the protocol extensions described in this document.11.  IANA Considerations   A flow specification consists of a sequence of flow components, which   are identified by a an 8-bit component type.  Types must be assigned   and interpreted uniquely.  The current specification defines types 1   though 12, with the value 0 being reserved.   For the purpose of this work, IANA has allocated values for two   SAFIs: SAFI 133 for IPv4 dissemination of flow specification rules   and SAFI 134 for VPNv4 dissemination of flow specification rules.   The following traffic filtering flow specification rules have been   allocated by IANA from the "BGP Extended Communities Type -   Experimental Use" registry as follows:      0x8006 - Flow spec traffic-rate      0x8007 - Flow spec traffic-action      0x8008 - Flow spec redirect      0x8009 - Flow spec traffic-remarking   IANA created and maintains a new registry entitled: "Flow Spec   Component Types".  The following component types have been   registered:      Type 1 - Destination Prefix      Type 2 - Source Prefix      Type 3 - IP Protocol      Type 4 - Port      Type 5 - Destination port      Type 6 - Source port      Type 7 - ICMP type      Type 8 - ICMP codeMarques, et al.             Standards Track                    [Page 19]

RFC 5575                   Flow Specification                August 2009      Type 9 - TCP flags      Type 10 - Packet length      Type 11 - DSCP      Type 12 - Fragment   In order to manage the limited number space and accommodate several   usages, the following policies defined byRFC 5226 [RFC5226] are   used:   +--------------+-------------------------------+   | Range        | Policy                        |   +--------------+-------------------------------+   | 0            | Invalid value                 |   | [1 .. 12]    | Defined by this specification |   | [13 .. 127]  | Specification Required        |   | [128 .. 255] | First Come First Served       |   +--------------+-------------------------------+   The specification of a particular "flow component type" must clearly   identify what the criteria used to match packets forwarded by the   router is.  This criteria should be meaningful across router hops and   not depend on values that change hop-by-hop such as TTL or Layer 2   encapsulation.   The "traffic-action" extended community defined in this document has   46 unused bits, which can be used to convey additional meaning.  IANA   created and maintains a new registry entitled: "Traffic Action   Fields".  These values should be assigned via IETF Review rules only.   The following traffic-action fields have been allocated:      47 Terminal Action      46 Sample      0-45 Unassigned12.  Acknowledgments   The authors would like to thank Yakov Rekhter, Dennis Ferguson, Chris   Morrow, Charlie Kaufman, and David Smith for their comments.   Chaitanya Kodeboyina helped design the flow validation procedure.   Steven Lin and Jim Washburn ironed out all the details necessary to   produce a working implementation.Marques, et al.             Standards Track                    [Page 20]

RFC 5575                   Flow Specification                August 200913.  Normative References   [IEEE.754.1985]  Institute of Electrical and Electronics Engineers,                    "Standard for Binary Floating-Point Arithmetic",                    IEEE Standard 754, August 1985.   [RFC0793]        Postel, J., "Transmission Control Protocol", STD 7,RFC 793, September 1981.   [RFC2119]        Bradner, S., "Key words for use in RFCs to Indicate                    Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2474]        Nichols, K., Blake, S., Baker, F., and D. Black,                    "Definition of the Differentiated Services Field (DS                    Field) in the IPv4 and IPv6 Headers",RFC 2474,                    December 1998.   [RFC4271]        Rekhter, Y., Li, T., and S. Hares, "A Border Gateway                    Protocol 4 (BGP-4)",RFC 4271, January 2006.   [RFC4303]        Kent, S., "IP Encapsulating Security Payload (ESP)",RFC 4303, December 2005.   [RFC4360]        Sangli, S., Tappan, D., and Y. Rekhter, "BGP                    Extended Communities Attribute",RFC 4360,                    February 2006.   [RFC4364]        Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual                    Private Networks (VPNs)",RFC 4364, February 2006.   [RFC4760]        Bates, T., Chandra, R., Katz, D., and Y. Rekhter,                    "Multiprotocol Extensions for BGP-4",RFC 4760,                    January 2007.   [RFC5226]        Narten, T. and H. Alvestrand, "Guidelines for                    Writing an IANA Considerations Section in RFCs",BCP 26,RFC 5226, May 2008.Marques, et al.             Standards Track                    [Page 21]

RFC 5575                   Flow Specification                August 2009Authors' Addresses   Pedro Marques   Cisco Systems   170 West Tasman Drive   San Jose, CA  95134   US   EMail: roque@cisco.com   Nischal Sheth   Juniper Networks   1194 N. Mathilda Ave.   Sunnyvale, CA  94089   US   EMail: nsheth@juniper.net   Robert Raszuk   Cisco Systems   170 West Tasman Drive   San Jose, CA  95134   US   EMail: raszuk@cisco.com   Barry Greene   Juniper Networks   1194 N. Mathilda Ave.   Sunnyvale, CA  94089   US   EMail: bgreene@juniper.net   Jared Mauch   NTT America   101 Park Ave   41st Floor   New York, NY  10178   US   EMail: jmauch@us.ntt.net   Danny McPherson   Arbor Networks   EMail: danny@arbor.netMarques, et al.             Standards Track                    [Page 22]