Movatterモバイル変換


[0]ホーム

URL:


[RFC Home] [TEXT|PDF|HTML] [Tracker] [IPR] [Info page]

Obsoleted by:8139 PROPOSED STANDARD
Updated by:7180
Internet Engineering Task Force (IETF)                        R. PerlmanRequest for Comments: 6439                                    Intel LabsUpdates:6325                                            D. Eastlake 3rdCategory: Standards Track                                          Y. LiISSN: 2070-1721                                      Huawei Technologies                                                             A. Banerjee                                                           Cisco Systems                                                                   F. Hu                                                         ZTE Corporation                                                           November 2011Routing Bridges (RBridges): Appointed ForwardersAbstract   The IETF TRILL (TRansparent Interconnection of Lots of Links)   protocol provides least cost pair-wise data forwarding without   configuration in multi-hop networks with arbitrary topology, safe   forwarding even during periods of temporary loops, and support for   multipathing of both unicast and multicast traffic.  TRILL   accomplishes this by using IS-IS (Intermediate System to Intermediate   System) link state routing and by encapsulating traffic using a   header that includes a hop count.  Devices that implement TRILL are   called "RBridges" (Routing Bridges).   TRILL supports multi-access LAN (Local Area Network) links that can   have multiple end stations and RBridges attached.  Where multiple   RBridges are attached to a link, native traffic to and from end   stations on that link is handled by a subset of those RBridges called   "Appointed Forwarders", with the intent that native traffic in each   VLAN (Virtual LAN) be handled by at most one RBridge.  The purpose of   this document is to improve the documentation of the Appointed   Forwarder mechanism; thus, it updatesRFC 6325.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6439.Perlman, et al.              Standards Track                    [Page 1]

RFC 6439             RBridges: Appointed Forwarders        November 2011Copyright Notice   Copyright (c) 2011 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   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Table of Contents1. Introduction ....................................................21.1. Terminology and Acronyms ...................................32. Appointed Forwarders and Their Appointment ......................42.1. Appointment Effects of DRB Elections .......................52.2. Appointment and Removal by the DRB .........................52.2.1. Processing Forwarder Appointments ...................62.2.2. Frequency of Appointments ...........................72.2.3. Appointed Forwarders Limit ..........................82.3. Local Configuration Action Appointment Effects .............82.4. VLAN Mapping within a Link .................................93. The Inhibition Mechanism ........................................94. Inhibited Appointed Forwarder Behavior .........................115. Multiple Ports on the Same Link ................................126. Security Considerations ........................................127. Acknowledgements ...............................................138. References .....................................................138.1. Normative References ......................................138.2. Informative References ....................................13   Appendix. VLAN Inhibition Example .................................141.  Introduction   The IETF TRILL (TRansparent Interconnection of Lots of Links)   protocol [RFC6325] provides optimal pair-wise data frame forwarding   without configuration in multi-hop networks with arbitrary topology,   safe forwarding even during periods of temporary loops, and support   for multipathing of both unicast and multicast traffic.  TRILL   accomplishes this by using IS-IS (Intermediate System to Intermediate   System) [IS-IS] [RFC1195] link state routing and encapsulating   traffic using a header that includes a hop count.  The designPerlman, et al.              Standards Track                    [Page 2]

RFC 6439             RBridges: Appointed Forwarders        November 2011   supports VLANs (Virtual Local Area Networks) and optimization of the   distribution of multi-destination frames based on VLANs and IP-   derived multicast groups.  Devices that implement TRILL are called   "RBridges" (Routing Bridges).Section 2 of [RFC6327] explains the environment for which the TRILL   protocol is designed and the differences between that environment and   the typical Layer 3 routing environment.   TRILL supports multi-access LAN (Local Area Network) links that can   have multiple end stations and RBridges attached.  Where multiple   RBridges are attached to a link, native traffic to and from end   stations on that link is handled by a subset of those RBridges called   "Appointed Forwarders", with the intent that native traffic in each   VLAN be handled by at most one RBridge.  An RBridge can be Appointed   Forwarder for many VLANs.   The purpose of this document is to improve the documentation of the   Appointed Forwarder mechanism; thus, it updatesRFC 6325.  It   includes reference implementation details.  Alternative   implementations that interoperate on the wire are permitted.   The Appointed Forwarder mechanism is irrelevant to any link on which   end station service is not offered.  This includes links configured   as point-to-point IS-IS links and any link with all RBridge ports on   that link configured as trunk ports.  (In TRILL, configuration of a   port as a "trunk port" just means that no end station service will be   provided.  It does not imply that all VLANs are enabled on that   port.)   The Appointed Forwarder mechanism has no effect on the formation of   adjacencies, the election of the Designated RBridge (DRB) for a link,   MTU matching, or pseudonode formation.  Those topics are covered in   [RFC6327].  Furthermore, Appointed Forwarder status has no effect on   the forwarding of TRILL Data frames.  It only affects the handling of   native frames.   For other aspects of the TRILL base protocol, see [RFC6325] and   [RFC6327].  Familiarity with [RFC6325] and [RFC6327] is assumed in   this document.  In case of conflict between this document and   [RFC6325], this document prevails.1.1.  Terminology and Acronyms   This document uses the acronyms defined in [RFC6325].   A "trunk port" is a port configured with the "end station service   disable" bit on, as described inSection 4.9.1 of [RFC6325].Perlman, et al.              Standards Track                    [Page 3]

RFC 6439             RBridges: Appointed Forwarders        November 2011   In this document, the term "link" means "bridged LAN", that is to say   some combination of physical links with zero or more bridges, hubs,   repeaters, or the like.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" in this document are to be interpreted as described in   [RFC2119].2.  Appointed Forwarders and Their Appointment   The Appointed Forwarder on a link for VLAN-x is the RBridge that   ingresses native frames from the link and egresses native frames to   the link in VLAN-x.  By default, the DRB (Designated RBridge) on a   link is in charge of native traffic for all VLANs on the link.  The   DRB may, if it wishes, act as Appointed Forwarder for any VLAN and it   may appoint other RBridges that have ports on the link as Appointed   Forwarder for one or more VLANs.   It is important that there not be two Appointed Forwarders on a link   that are ingressing and egressing native frames for the same VLAN at   the same time.  Should this occur, it could form a loop where frames   are not protected by a TRILL Hop Count for part of the loop.  (Such a   condition can even occur through two Appointed Forwarders for two   different VLANs, VLAN-x and VLAN-y, if ports or bridges inside the   link are configured to map frames between VLAN-x and VLAN-y as   discussed inSection 2.4.)  While TRILL tries to avoid such   situations, for loop safety there is also an "inhibition" mechanism   (seeSection 3) that can cause an RBridge that is an Appointed   Forwarder to not ingress or egress native frames.   As discussed inSection 5, an RBridge may have multiple ports on a   link.  As discussed in [RFC6327], if there are multiple ports with   the same Media Access Control (MAC) address on a link, all but one   will be suspended.  The case of multiple ports on a link for one   RBridge and the case of multiple ports with the same MAC address on a   link and combinations of these cases are fully accommodated; however,   multiple ports on a link for one RBridge is expected to be a rare   condition and duplicate MAC addresses are not recommended by either   TRILL or IEEE 802.1 standards.   Appointed Forwarder status has no effect on the forwarding of TRILL   Data frames.  It only affects the handling of native frames.Perlman, et al.              Standards Track                    [Page 4]

RFC 6439             RBridges: Appointed Forwarders        November 2011   There are three mechanisms by which an RBridge can be appointed or   un-appointed as Appointed Forwarder: as a result of the DRB elections   [RFC6327] as discussed inSection 2.1, as a result of action by the   DRB as discussed inSection 2.2, as a result of a local configuration   action as discussed inSection 2.3.2.1.  Appointment Effects of DRB Elections   When an RBridge believes that it has become the DRB on a link, by   default, it can act as Appointed Forwarder for any VLANs on that link   that it chooses as long as its port is not configured as a trunk port   and has that VLAN enabled (or at least one of its ports meets these   criteria, if it has more than one port on the link).   An RBridge loses all Appointed Forwarder status when:   1.  it decides that it has lost the status of being the DRB for a       link; or   2.  it observes a change in the RBridge that is the DRB for the link       without itself becoming the DRB.   In the rare corner case where an RBridge has more than one port on a   link, one of which was previously the DRB election winner but has   just lost the DRB election to a different port of the same RBridge   (possibly due to management configuration of port priorities), there   is no change in which RBridge is the DRB.  Therefore, neither of the   above points applies and there is no change in Appointed Forwarder   status.2.2.  Appointment and Removal by the DRB   The DRB may appoint other RBridges on the link through inclusion of   one or more Appointed Forwarders sub-TLVs [RFC6326] in a TRILL Hello   it sends on the Designated VLAN out the port that won the DRB   election.  When the DRB sends any appointments in a TRILL Hello, it   must send all appointments for that link in that Hello.  Any previous   appointment not included is implicitly revoked.   Although the DRB does not need to announce the VLANs for which it has   chosen to act as Appointed Forwarder by sending appoints for itself,   if the DRB wishes to revoke all appointments for RBridges other than   itself on the link, it is recommended that it send a TRILL Hello with   an appointment for itself for some VLAN.   The DRB MUST NOT send any appointments on a link unless its DRB   inhibition timer (seeSection 3) for that link is expired.Perlman, et al.              Standards Track                    [Page 5]

RFC 6439             RBridges: Appointed Forwarders        November 2011   How the DRB decides what other RBridges on the link, if any, to   appoint forwarder for which VLANs is beyond the scope of this   document.2.2.1.  Processing Forwarder Appointments   When a non-DRB RBridge that can offer end station service on a link   receives a TRILL Hello that is not discarded for one of the reasons   given in [RFC6327], it checks the source MAC address and the Port ID   and System ID in the Hello to determine if it is from the winning DRB   port.  If it is not from that port, any Appointed Forwarder sub-TLVs   in the Hello are ignored, and there is no change in the receiving   RBridge's Appointed Forwarder status.  Also, if no Appointed   Forwarder sub-TLVs are present in the TRILL Hello, there is no change   in the receiver's Appointed Forwarder status.   However, if the TRILL Hello is from the winning DRB port and the   Hello includes one or more Appointed Forwarder sub-TLVs, then the   receiving RBridge becomes appointed for the VLANs that are both   listed for it in the Hello and are enabled on the receiving port.   (If the appointment includes VLAN IDs 0x000 or 0xFFF, they are   ignored, but any other VLAN IDs are still effective.)  If the   receiver was Appointed Forwarder for any other VLANs, its Appointed   Forwarder status for such other VLANs is revoked.  For example, if   none of these sub-TLVs in a Hello appoints the receiving RBridge,   then it loses all Appointed Forwarder status and is no longer   Appointed Forwarder for any VLAN on the port where the Hello was   received.   The handling of one or more Appointed Forwarder sub-TLVs in a Hello   from the winning port that appoints the receiving RBridge is as   follows.  An appointment in an Appointed Forwarder sub-TLV is for a   specific RBridge and a contiguous interval of VLAN IDs; however, as   stated above, it actually appoints that RBridge forwarder only for   the VLAN(s) in that range that are enabled on one or more ports that   RBridge has on the link (ignoring any ports configured as trunk ports   or as IS-IS point-to-point ports).  If the RBridge was Appointed   Forwarder for any additional VLANs beyond the VLANs for which it was   being appointed, it loses Appointed Forwarder status for such   additional VLANs.   There is no reason for an RBridge to remember that it received a   valid appointment message for a VLAN that was ineffective because the   VLAN was not enabled on the port where the message was received or   because the port was a trunk or point-to-point port.  It does not   become Appointed Forwarder for such a VLAN just because that VLAN is   later enabled or the port later reconfigured.Perlman, et al.              Standards Track                    [Page 6]

RFC 6439             RBridges: Appointed Forwarders        November 2011   It should be straightforward for the DRB to send, within one Hello,   the appointments for several dozen VLAN IDs or several dozen blocks   of contiguous VLAN IDs.  Should the VLANs the DRB wishes to appoint   be inconveniently distributed, for example, the proverbial case where   the DRB RB1 wishes to appoint RB2 forwarder for all even-numbered   VLANs and appoint RB3 forwarder for all odd-numbered VLANs, the   following method may be used.  The network manager normally controls   what VLANs are enabled on RBridge port.  Thus, the network manager   can appoint an RBridge forwarder for an arbitrary set of scattered   VLANs by enabling only those VLANs on the relevant port (or ports)   and then having the DRB send an appointment that appears to appoint   the target RBridge forwarder for all VLANs.  However, for proper   operation and inter-RBridge communication, the Designated VLAN for a   link SHOULD be enabled on all RBridge ports on that link, and it may   not be desired to appoint the RBridge forwarder for the Designated   VLAN.  Thus, in the general case, it would require two appointments,   although it would still only require one appointment if the   Designated VLAN were an extreme low or high value such as VLAN 0xFFE   or the default VLAN 1.   For example, assume the DRB wants RB2 to be Appointed Forwarder for   all even-numbered VLANs and the Designated VLAN for the link is VLAN   101.  The network manager could cause all even-numbered VLANs plus   VLAN 101 to be enabled on the relevant port of RB2 and then, with the   desired effect, cause the DRB to send appointments to RB2 appointing   it forwarder for all VLANs from 1 through 100 and from 102 through   4,094.   Should the network manager have misconfigured the enabled VLANs and   Appointed Forwarders, resulting in two RBridges believing they are   Appointed Forwarders for the same VLAN, then item 4 inSection 3 will   cause one or more of the RBridges to be inhibited for that VLAN.2.2.2.  Frequency of Appointments   It is not necessary for the DRB to include the forwarder appointments   in every TRILL Hello that it sends on the Designated VLAN for a link.   For loop safety, every RBridge is required to indicate, in every   TRILL Hello it sends in VLAN-x on a link, whether it is an Appointed   Forwarder for VLAN-x for that link (see item 4 inSection 3).  It is   also RECOMMENDED that the DRB have all VLANs for which end station   service will be offered on the link as well as the Designated VLAN,   enabled.  Thus, the DRB will generally be informed by other RBridges   on the link of the VLANs for which they believe they are Appointed   Forwarder.  If this matches the appointments the DRB wishes to make,   it is not required to re-send its forwarder appointments; however,   for robustness, especially in cases such as VLAN misconfigurations inPerlman, et al.              Standards Track                    [Page 7]

RFC 6439             RBridges: Appointed Forwarders        November 2011   a bridged LAN link, it is RECOMMENDED that the DRB send its forwarder   appointments on the Designated VLAN at least once per its Holding   Time on the port that won the DRB election.2.2.3.  Appointed Forwarders Limit   The mechanism of DRB forwarder appointment and the limited length of   TRILL Hellos impose a limit on the number of RBridges on a link that   can be Appointed Forwarders.  To obtain a conservative estimate,   assume that no more than 1000 bytes are available in a TRILL Hello   for such appointments.  Assume it is desired to appoint various   RBridges on a link forwarder for arbitrary non-intersecting sets of   VLANs.  Using the technique discussed above would generally require   two appointments, or 12 bytes, per RBridge.  With allowance for   sub-TLV and TLV overhead, appointments for 83 RBridges would fit in   under 1000 bytes.  Including the DRB, this implies a link with 84 or   more RBridges attached.  Links with more than a handful of RBridges   attached are expected to be rare.   Note: If the Designated VLAN were an extreme low or high value, such   as VLAN 1, which is the default and may be a common value in   practice, only 6 bytes per RBridge would be required.  This would   permit twice as many different Appointed Forwarder RBridges than   indicated by the general analysis above or, alternatively, would take   only half as much space to appoint the same number of Appointed   Forwarders.   Unnecessary changes in Appointed Forwarders SHOULD NOT be made as   they may result in transient lack of end station service.  Large   numbers of Appointed Forwarders on a link (in excess of 65) are NOT   RECOMMENDED due to the complexity of their establishment and   maintenance.2.3.  Local Configuration Action Appointment Effects   Disabling VLAN-x at an RBridge port cancels any Appointed Forwarder   status that RBridge has for VLAN-x unless VLAN-x is enabled on some   other port that the RBridge has connected to the same link.   Configuring a port as a trunk port or point-to-point port revokes any   Appointed Forwarder status that depends on enabled VLANs at that   port.   Causing a port to no longer be configured as a trunk or point-to-   point port or enabling VLAN-x on a port does not, in itself, cause   the RBridge to become an Appointed Forwarder for the link that port   is on.  However, such actions can allow the port's RBridge to become   Appointed Forwarder by choice if it is the DRB or by appointment, if   it is not the DRB on the link.Perlman, et al.              Standards Track                    [Page 8]

RFC 6439             RBridges: Appointed Forwarders        November 20112.4.  VLAN Mapping within a Link   TRILL Hellos include a field that is set to the VLAN in which they   are sent.  If they arrive on a different VLAN, then VLAN mapping is   occurring within the link.  (Such VLAN mapping within a link between   RBridges should not be confused with VLAN mapping inside an RBridge   [VLANMAP]).  VLAN mapping between VLAN-x and VLAN-y can lead to a   loop if the Appointed Forwarders for the VLANs are different.  If   such mapping within a link was allowed and occurred on two or more   links so that there was a cycle of VLAN mappings, a broadcast frame,   for example, would loop forever.   To prevent this potential problem, if the DRB on a link detects VLAN   mapping by receiving a Hello in VLAN-x that was sent on VLAN-y, it   MUST make or revoke appointments so as to assure that the same   RBridge (possibly the DRB) is the Appointed Forwarder on the link for   both VLAN-x and VLAN-y.3.  The Inhibition Mechanism   An RBridge has, for every link on which it can offer end station   service (that is every link for which it can act as an Appointed   Forwarder), the following timers denominated in seconds:   - a DRB inhibition timer,   - a root change inhibition timer, and   - up to 4,094 VLAN inhibition timers, one for each legal VLAN ID.   The DRB and root change inhibition timers MUST be implemented.   The loss of native traffic due to inhibition will be minimized by   logically implementing a VLAN inhibition timer per each VLAN for   which end station service will ever be offered by the RBridge on the   link; this SHOULD be done.  (See the Appendix for an example   motivating VLAN inhibition timers.)  However, if implementation   limitations make a full set of such timers impractical, the VLAN   inhibition timers for more than one VLAN can, with care, be merged   into one timer.  In particular, an RBridge MUST NOT merge the VLAN   inhibition timers together for two VLANs if it is the Appointer   Forwarder for one and not for the other, as this can lead to   unnecessary indefinitely prolonged inhibition.  In the limit, there   will be safe operations, albeit with more native frame loss than   would otherwise be required, even if only two VLAN inhibition timers   are provided: one for VLANs for which the RBridge is the Appointed   Forwarder and one for all other VLANs.  At least two VLAN inhibitionPerlman, et al.              Standards Track                    [Page 9]

RFC 6439             RBridges: Appointed Forwarders        November 2011   timers MUST be implemented.  Where a VLAN inhibition timer represents   more than one VLAN, an update or test that would have been done to   the timer for any of the VLANs is performed on the merged timer.   These timers are set as follows:   1.  On booting or management reset, each port will have its own set       of timers, even if two or more such ports are on the same link,       because the RBridge will not have had a chance to learn that yet.       All inhibition timers are set to expired except the DRB       inhibition timer that is set in accordance with item 2 below.       The DRB inhibition timer is handled differently because each port       will initially believe it is the DRB.   2.  When an RBridge decides that it has become the DRB on a link,       including when it is first booted or reset by management, it sets       the DRB inhibition timer to the Holding Time of its port on that       link that won the DRB election.   3.  When an RBridge decides that it has lost DRB status on a link, it       sets the DRB inhibition timer to expired.       Note: In the rare corner case where one port of an RBridge was       the DRB election winner, but later lost the DRB election to a       different port of the same RBridge on that link (perhaps due to       management configuration of port priority), neither 2 nor 3 above       applies, and the DRB timer is not changed.   4.  When an RBridge RB1 receives a TRILL Hello asserting that the       sender is the Appointed Forwarder that either (1) arrives on       VLAN-x or (2) was sent on VLAN-x as indicated inside the Hello,       then RB1 sets its VLAN-x inhibition timer for the link to the       maximum of that timer's existing value and the Holding Time in       the received Hello.  An RBridge MUST maintain VLAN inhibition       timers for a link to which it connects if it can offer end       station service on that link even if it is not currently       Appointed Forwarder for any VLAN on that link.   5.  When an RBridge RB1 enables VLAN-x on a port connecting to a link       and VLAN-x was previously not enabled on any of RB1's ports on       that link, it sets its VLAN inhibition timer for VLAN-x for that       link to its Holding Time for that port.  This is done even if the       port is configured as a trunk or point-to-point port as long as       there is some chance it might later be configured not to be a       trunk or point-to-point port.Perlman, et al.              Standards Track                   [Page 10]

RFC 6439             RBridges: Appointed Forwarders        November 2011   6.  When an RBridge detects a change in the common spanning tree root       bridge on a port, it sets its root change inhibition timer for       the link to an amount of time that defaults to 30 seconds and is       configurable to any value from 30 down to zero seconds.  This       condition will not occur unless the RBridge is receiving Bridge       PDU (BPDUs) on the port from an attached bridged LAN.  It is safe       to configure this inhibition time to the settling time of an       attached bridged LAN.  For example, if it is known that Rapid       Spanning Tree Protocol (RSTP [802.1Q]) is running throughout the       attached bridged LAN, it should be safe to configure this       inhibition time to 7 seconds or, if the attached bridges have       been configured to have a minimum Bridge Hello Timer, safe to       configure it to 4 seconds.  Note that, while an RBridge could       determine what version of spanning tree is running on the       physical link between it and any directly connected bridge by       examination of the BPDUs it receives, it could not tell if       inter-bridge links beyond those directly connected bridges were       running classic Spanning Tree Protocol (STP), which might require       the root change inhibition timer to be set to 30 seconds for       safety.   7.  When an RBridge decides that one of its ports (or a set of its       ports) P1 is on the same link as another of its ports (or set of       its ports) P2, then the inhibition timers are merged to a single       set of inhibition timers by using the maximum value of the       corresponding timers.   8.  When an RBridge decides that a set of its ports that it had been       treating as being on the same link are no longer on the same       link, those ports will necessarily be on two or more links (one       link per port in the limit).  This is handled by cloning a copy       of the timers for each of the two or more links to which the       RBridge has decided these ports connect.4.  Inhibited Appointed Forwarder Behavior   An Appointed Forwarder for a link is inhibited for VLAN-x if:   1.  its DRB inhibition timer for that link is not expired, or   2.  its root change inhibition timer for that link is not expired, or   3.  its VLAN inhibition timer for that link for VLAN-x is not       expired.   If a VLAN-x Appointed Forwarder for a link is inhibited and receives   a TRILL Data frame whose encapsulated frame is in VLAN-x and would   normally be egressed to that link, it decapsulates the native framePerlman, et al.              Standards Track                   [Page 11]

RFC 6439             RBridges: Appointed Forwarders        November 2011   as usual.  However, it does not output it to or queue it for that   link, although, if appropriate (for example, the frame is multi-   destination), it may output it to or queue it for other links.   If a VLAN-x Appointed Forwarder for a link is inhibited and receives   a native frame in VLAN-x that would normally be ingressed from that   link, the native frame is ignored except for address learning.   An RBridge with one or more unexpired inhibition timers, possibly   including an unexpired inhibition timer for VLAN-x, is still required   to indicate in TRILL Hellos it sends on VLAN-x whether or not it is   Appointed Forwarder for VLAN-x for the port on which it sends the   Hello.   Inhibition has no effect on the receipt or forwarding of TRILL Data   frames.5.  Multiple Ports on the Same Link   An RBridge may have multiple ports on the same link.  Some of these   ports may be suspended due to MAC address duplication as described in   [RFC6327].  Suspended ports never ingress or egress native frames.   If an RBridge has one or more non-suspended ports on a link and those   ports offer end station service, that is, those ports are not   configured as point-to-point or trunk ports, then that RBridge is   eligible to be an Appointed Forwarder for that link.  It can become   Appointed Forwarder either by its choice, because it is the DRB, or   by appointment by the DRB as described in Sections2.1 and2.2.   If an RBridge that is the Appointed Forwarder for VLAN-x on a link   has multiple non-suspended ports on that link, it may load share the   task of ingressing and egressing VLAN-x native frames across those   ports however it chooses, as long as there is no case in which a   frame it egresses onto the link from one port can be ingressed on   another of its ports, creating a loop.  If the RBridge is the   Appointed Forwarder for multiple VLANs, a straightforward thing to do   would be to partition those VLANs among the ports it has on the link.6.  Security Considerations   This memo provides improved documentation of the TRILL Appointed   Forwarder mechanism.  It does not change the security considerations   of the TRILL base protocol.  SeeSection 6 of [RFC6325].Perlman, et al.              Standards Track                   [Page 12]

RFC 6439             RBridges: Appointed Forwarders        November 20117.  Acknowledgements   The authors of [RFC6325] and [RFC6327], those listed in the   Acknowledgements section of [RFC6325] and [RFC6327], and Ron Bonica,   Stewart Bryant, Linda Dunbar, Les Ginsberg, Erik Nordmark, Dan   Romascanu, and Mike Shand are hereby thanked for their contributions.8.  References   Normative and Informative references for this document are listed   below.8.1.  Normative References   [802.1Q]    IEEE 802.1, "IEEE Standard for Local and metropolitan               area networks - Virtual Bridged Local Area Networks",               IEEE Std 802.1Q-2011, May 2011.   [IS-IS]     ISO/IEC 10589:2002, Second Edition, "Intermediate System               to Intermediate System Intra-Domain Routeing Exchange               Protocol for use in Conjunction with the Protocol for               Providing the Connectionless-mode Network Service (ISO               8473)", 2002.   [RFC1195]   Callon, R., "Use of OSI IS-IS for routing in TCP/IP and               dual environments",RFC 1195, December 1990.   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC6325]   Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.               Ghanwani, "Routing Bridges (RBridges): Base Protocol               Specification",RFC 6325, July 2011.   [RFC6326]   Eastlake, D., Banerjee, A., Dutt, D., Perlman, R., and A.               Ghanwani, "Transparent Interconnection of Lots of Links               (TRILL) Use of IS-IS",RFC 6326, July 2011.   [RFC6327]   Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D.,               and V. Manral, "Routing Bridges (RBridges): Adjacency",RFC 6327, July 2011.8.2.  Informative References   [VLANMAP]   Perlman, R., Dutt, D., Banerjee, A., Rijhsinghani, A.,               and D.  Eastlake, "RBridges: Campus VLAN and Priority               Regions", Work in Progress, October 2011.Perlman, et al.              Standards Track                   [Page 13]

RFC 6439             RBridges: Appointed Forwarders        November 2011Appendix.  VLAN Inhibition Example   The per-VLAN inhibition timers (or the equivalent) are needed to be   loop safe in the case of misconfigured bridges on a link.   For a simple example, assume that RB1 and RB2 are the only RBridges   on the link, that RB1 is higher priority to be the DRB, and that they   both want VLAN 1 (the default) to be the Designated VLAN.  However,   there is a bridge between them configured so that RB1 can see all the   frames sent by RB2 but none of the frames from RB1 can get through to   RB2.   Both will think they are the DRB.  RB1 because it is higher priority   even though it sees the Hellos from RB2, and RB2 because it doesn't   see the Hellos from RB1 and therefore thinks it is highest priority.   Say RB1 chooses to act as Appointed Forwarder for VLANs 2 and 3 while   RB2 chooses to act as Appointed Forwarder for VLANs 3 and 4.  There   is no problem with VLANs 2 and 4 but if you do not do something about   it, you could have a loop involving VLAN 3.  RB1 will see the Hellos   RB2 issues on VLAN 3 declaring itself Appointed Forwarder, so RB1   will be inhibited on VLAN 3.  RB2 does not see the Hellos issued by   RB1 on VLAN 3, so RB2 will become uninhibited and will handle VLAN 3   native traffic.   However, this situation may change.  RB2 might crash, the bridge   might crash, or RB2 might be reconfigured so it no longer tried to   act as Appointed Forwarder for VLAN 3, or other issues may occur.   So, RB1 has to maintain a VLAN 3 inhibition timer, and if it sees no   Hellos from any other RBridge on the link claiming to be Appointed   Forwarder for VLAN 3 in a long enough time, then RB1 becomes   uninhibited for that VLAN on the port in question and can handle end   station traffic in VLAN 3.Perlman, et al.              Standards Track                   [Page 14]

RFC 6439             RBridges: Appointed Forwarders        November 2011Authors' Addresses   Radia Perlman   Intel Labs   2200 Mission College Blvd.   Santa Clara, CA 95054 USA   Phone: +1-408-765-8080   EMail: Radia@alum.mit.edu   Donald Eastlake 3rd   Huawei Technologies   155 Beaver Street   Milford, MA 01757 USA   Phone: +1-508-333-2270   EMail: d3e3e3@gmail.com   Yizhou Li   Huawei Technologies   101 Software Avenue,   Nanjing 210012, China   Phone: +86-25-56622310   EMail: liyizhou@huawei.com   Ayan Banerjee   Cisco Systems   170 West Tasman Drive   San Jose, CA 95134 USA   Phone: +1-408-333-7149   EMail: ayabaner@cisco.com   Fangwei Hu   ZTE Corporation   889 Bibo Road   Shanghai 201203   China   Phone: +86-21-68896273   EMail: hu.fangwei@zte.com.cnPerlman, et al.              Standards Track                   [Page 15]

[8]ページ先頭

©2009-2025 Movatter.jp