TRILL Working Group Donald Eastlake INTERNET-DRAFT Yizhou Li Intended status: Proposed Standard Huawei Obsoletes: 6439 Mohammed Umair Updates: 6325, 7177 IPinfusion Ayan Banerjee Cisco Hu Fangwei ZTE Expires: July 4, 2016 January 5, 2016 TRILL: Appointed Forwarders <draft-ietf-trill-rfc6439bis-01.txt> Abstract TRILL supports multi-access LAN (Local Area Network) links where a single link can have multiple end stations and TRILL switches attached. Where multiple TRILL switches are attached to a link, native traffic to and from end stations on that link is handled by a subset of those TRILL switches called "Appointed Forwarders", with the intent that native traffic in each VLAN be handled by at most one TRILL switch. This document clarifies and updates the Appointed Forwarder mechanism. It updates RFC 6325, updates RFC 7177, and obsoletes RFC 6439. Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Distribution of this document is unlimited. Comments should be sent to the TRILL working group mailing list <trill@ietf.org>. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. D. Eastlake, et al [Page 1]
INTERNET-DRAFT TRILL: Appointed Forwarders Table of Contents 1. Introduction...........................................4 1.1 Appointed Forwarders and Active-Active.................5 1.2 Terminology and Acronyms...............................5 2. Appointed Forwarders and Their Appointment..............7 2.1 The Appointment Databases and DRB Actions..............8 2.2 Appointment Effects of DRB Elections...................9 2.2.1 Processing Forwarder Appointments in Hellos.........10 2.2.2 Frequency of Hello Appointments.....................12 2.2.3 Appointed Forwarders Hello Limit....................12 2.3 Local Configuration Actions Appointment Effects.......13 2.4 Overload and Appointed Forwarders.....................13 2.5 VLAN Mapping within a Link............................13 3. The Inhibition Mechanism...............................15 3.1 Inhibited Appointed Forwarder Behavior................17 3.2 Root Change Inhibition Optimizations..................17 3.2.1 Change Optimization One.............................18 3.2.2 Change Optimization Two.............................18 3.2.3 Settling Detection Optimization.....................18 4. Optional TRILL Hello Reduction.........................20 5. Multiple Ports on the Same Link........................22 6. Port-Shutdown Messages.................................23 6.1 Planned Shutdown and Hellos...........................23 6.2 Port-Shutdown Message Structure.......................23 6.3 Port-Shutdown Message Transmission....................24 6.4 Port-Shutdown Message Reception.......................25 6.5 Port-Shutdown Message Security........................25 6.6 Port-Shutdown Configuration...........................25 7. FGL-VLAN Mapping Consistency Checking..................27 8. Support of E-L1CS......................................28 8.1 Backwards Compatibility...............................28 9. Security Considerations................................29 10. Code Points and Data Structures.......................30 10.1 IANA Considerations..................................30 10.2 Appointment Bitmap APPsub-TLV........................30 10.3 Appointment List APPsub-TLV..........................31 10.4 FGL-VLAN Mapping Bitmap APPsub-TLV...................32 10.5 FGL-VLAN Mapping Pairs APPsub-TLV....................34 Normative References......................................35 Informative References....................................36 D. Eastlake, et al [Page 2]
INTERNET-DRAFT TRILL: Appointed Forwarders Table of Contents (continued) Acknowledgements..........................................37 Authors' Addresses........................................38 Appendix A: VLAN Inhibition Example.......................39 Appendix B: Changes to RFCs 6325, 6439, 7177..............40 Appendix C: Multi-Link VLAN Mapping Loop Example..........41 Appendix Z: Change Record.................................43 D. Eastlake, et al [Page 3]
INTERNET-DRAFT TRILL: Appointed Forwarders 1. Introduction The IETF TRILL protocol [RFC6325] [rfc7180bis] provides optimal pair- wise data frame forwarding without configuration in multi-hop networks with arbitrary topology and link technology, 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] [RFC7176] link state routing and encapsulating traffic using a header that includes a hop count. The design supports VLANs, 24-bit fine grained labels [RFC7172], and optimization of the distribution of multi-destination frames based on VLANs and multicast groups. Devices that implement TRILL are called TRILL switches or "RBridges" (Routing Bridges). Section 2 of [RFC7177] discusses 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 TRILL switches attached. Where multiple TRILL switches are attached to a link, native traffic to and from end stations on that link is handled by a subset of those switches called "Appointed Forwarders", with the intent that native traffic in each VLAN be handled by at most one switch. A TRILL switch can be Appointed Forwarder for many VLANs. The purpose of this document is to update and improve the Appointed Forwarder mechanism and free it from the limitations imposed by the requirement in its initial design that all appointments fit within a TRILL Hello PDU. This is accomplished by requiring support of link scoped FS-LSPs (Section 7) and proving for appointment information to be sent in those LSPs. In addition this document provides a number of optional features to (1) detect inconsistent VLAN to FGL [RFC7172] mappings among the TRILL switch ports on a link as discussed in Section 7, (2) expedite notification of ports going down so that Appointed Forwarders can be adjusted as discussed in Section 6, and (3) reduce or eliminate the need to "inhibition" of ports for loop safety as discussed in Section 3.2. This documents obsoletes [RFC6439], updates [RFC6325], and updates [RFC7177], as described in Appendix B. It also 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 TRILL switch 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 D. Eastlake, et al [Page 4]
INTERNET-DRAFT TRILL: Appointed Forwarders 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 [RFC7177]. Furthermore, Appointed Forwarder status has no effect on the forwarding of TRILL Data frames; it only affects the handling of native frames to and from end stations. For other aspects of the TRILL base protocol, see [RFC6325], [RFC7177], and [rfc7180bis]. In case of conflict between this document and [RFC6325] or [RFC7177], this document prevails. 1.1 Appointed Forwarders and Active-Active As discussed in [RFC7379], TRILL active-active provides support for end stations connected to multiple edge TRILL switches where these connections are separate links. Since TRILL Hellos are not forwarded between these links, the Appointed Forwarder mechanism as described herein operates separately on each such link. 1.2 Terminology and Acronyms This document uses the acronyms and terms defined in [RFC6325], some of which are repeated below for convenience, and additional acronyms and terms listed below. DRB: Designated RBridge. The RBridge on a link elected as specified in [RFC7177] to handle certain decisions and tasks for that link including forwarder appointent as specified herein. E-L1CS: Extended Level 1 Circuit Scoped (Section 8). FGL: Fine Grained Label [RFC7172]. FS-LSP: Flooding Scoped - Link State PDU (Section 8). Link: The means by which adjacent TRILL switches are connected. A TRILL link may be various technologies and, in the common case of Ethernet, can be a "bridged LAN", that is to say, some combination of Ethernet links with zero or more bridges, hubs, repeaters, or the like. LSDB: Link State Data Base. RBridge: An alternative name for a TRILL switch. D. Eastlake, et al [Page 5]
INTERNET-DRAFT TRILL: Appointed Forwarders TRILL: Transparent Interconnection of Lots of Links or Tunneled Routing in the Link Layer. TRILL switch: A device implementing the TRILL protocol. An alternative name for an RBridge. Trunk port: A TRILL switch port configured with the "end station service disable" bit on, as described in Section 4.9.1 of [RFC6325]. 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 in [RFC2119]. D. Eastlake, et al [Page 6]
INTERNET-DRAFT TRILL: Appointed Forwarders 2. Appointed Forwarders and Their Appointment The Appointed Forwarder on a link for VLAN-x is the TRILL switch (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 TRILL switches that have ports on the link as Appointed Forwarder for one or more VLANs. By definition, the DRB considers the other ports on the link to be the ports with which a DRB port has adjacency on that link [RFC7177]. If the DRB loses adjacency to a TRILL switch that it has appointed a forwarder and the native traffic that was being handled by that Appointed Forwarder is still to be ingressed and egressed, it SHOULD immediately appoint another forwarder or itself become forwarder for that traffic. 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 in Section 2.5.) While TRILL tries to avoid such situations, for loop safety there is also an "inhibition" mechanism (see Section 3) that can cause a TRILL switch that is an Appointed Forwarder to not ingress or egress native frames. Appointed Forwarder status and port "inhibition" have no effect on the reception, transmission, or forwarding of TRILL Data or TRILL IS-IS frames. Appointed Forwarder status and inhibition only affect the handling of native frames. As discussed in Section 5, an RBridge may have multiple ports on a link. As discussed in [RFC7177], if there are multiple ports with the same Media Access Control (MAC) address on the same link, all but one will be suspended. The case of multiple ports on a link for the same TRILL switch 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 the same TRILL switch is expected to be a rare condition and duplicate MAC addresses is not recommended by either TRILL or IEEE 802.1 standards. There are six mechanisms by which an RBridge can be appointed or un- appointed as Appointed Forwarder: (1) assumption of appointment, when the DRB decides to act as Appointed Forwarder for a VLAN, (2) Hello appointment, as a result of appointments sent by the DRB in TRILL Hellos, (3) E-L1CS appointment, as a result of appointments sent by the DRB in E-L1CS FS-LSPs, (4) as a result of the DRB elections D. Eastlake, et al [Page 7]
INTERNET-DRAFT TRILL: Appointed Forwarders [RFC7177] as discussed in Section 2.2, (5) as a result of a Port- Shutdown message as discussed in Section 6, and (6) as a result of a local configuration action as discussed in Section 2.3. Mechanisms 2 and 3 are covered in Section 2.1. 2.1 The Appointment Databases and DRB Actions The DRB MAY appoint other RBridges on the link as Appointed Forwarders through the mechanisms A and B described below. Each RBridge maintains two databases of appointment information: (1) its E-L1CS LSDB that shows appointments each RBridge on the link would make using mechanism A if it were the DRB, and (2) its Hello appointment database that shows the appointments most recently sent by the DRB in a TRILL Hello. The E-L1CS LSDB is semi-permanent and is only changed by E-L1CS FS-LSPs or IS-IS purges. The Hello appointment database is more transient and is completely reset by each Hello received from the DRB that contains any appointments and is also cleared under other circumstances as described below. An RBridge considers itself to be the Appointed Forwarder for VLAN-x if this is indicated by either its Hello appointment database or its E-L1CS LSDB entries from the DRB. The two mechanisms by which the DRB can appoint other RBridges on a link Appointed Forwarders are as follows: (A) The inclusion of one or more Appointed Forwarders sub-TLVs [RFC7176], Appointment Bitmap APPsub-TLVs (Section 10.2), or Appointment List APPsub-TLVs (Section 10.3) in E-L1CS LSPs it sends on a link. Appointments sent with this method will not be seen by legacy RBridges that do not support E-L1CS (Section 8). (B) The inclusion of one or more Appointed Forwarders sub-TLVs [RFC7176] 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 it is sending in Hellos for that link in that Hello. Any previous appointment it has sent in a Hello that is not included is implicitly revoked. To avoid the size limitations of the Hello PDU, it is RECOMMENDED that the E-L1CS FS-LSP method be used to distribute forwarder appointments and that all RBridges on a link advertise by this method the appointments they would make if they were DRB. However, if some RBridges on a link do not support E-L1CS FS-LSPs, then Hello appointments must be used for the DRB to appoint such legacy RBridges an Appointed Forwarder. D. Eastlake, et al [Page 8]
INTERNET-DRAFT TRILL: Appointed Forwarders 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 made in Hellos for RBridges other than itself on the link, it can do so by sending a TRILL Hello with just an appointment for itself for some VLAN. 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. Unnecessary changes in Appointed Forwarders SHOULD NOT be made as they may result in transient lack of end station service. 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 in Section 3 will cause one or more of the RBridges to be inhibited for that VLAN thus avoiding persistent loops. When forwarder appointments are being encoded for transmission, different patterns of VLANs are most efficiently encoded in different ways. The following table gives advice for the most efficient encoding: sub-TLV and Reference Pattern of VLAN IDs |enclosing TLV(s) and Reference ----------------- ------------------------------------ Blocks of consecutive VLANs Appointed Forwarders sub-TLV [RFC7176] |Router Capabilities TLV [RFC4971] |or MT Capabilities TLV [RFC6329] Scattered VLANs within a small range Appointment Bitmap APPsub-TLV (Section 10.2) |TRILL GENINFO TLV [RFC7357] Scattered VLANs over a large range Appointment List APPsub-TLV (Section 10.3) |TRILL GENINFO TLV [RFC7357] 2.2 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). D. Eastlake, et al [Page 9]
INTERNET-DRAFT TRILL: Appointed Forwarders An RBridge loses all Hello appointments and changes which E-L1CS FS- LSP appointments it uses as follows: 1. When it decides that it has lost the status of being the DRB for a link; or 2. When it observes a change in the RBridge that is the DRB for the link without itself becoming the DRB. In both cases, it loses all Hello appointments and switches to being Appointed Forwarder only for the appointments, if any, in its E-L1CS FS-LSP appointment database from the new DRB. In the corner case where a TRILL switch 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 TRILL switch on the same link (possibly due to management configuration of port priorities), there is no change in which TRILL switch is the DRB. Therefore, neither of the above points applies and there is no change in Appointed Forwarder status. 2.2.1 Processing Forwarder Appointments in Hellos 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 [RFC7177], 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 forwarder appointment sub- TLVs in the Hello are ignored, and there is no change in the receiving RBridge's Appointed Forwarder status due to that Hello. Also, if no forwarder appointment sub-TLVs are present in the TRILL Hello, there is no change in the receiver's Appointed Forwarder status due to that Hello. However, if the TRILL Hello is from the winning DRB port and the Hello includes one or more forwarder appointment sub-TLVs, then the receiving RBridge sets its Hello appointment database to be 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.) It then becomes Appointed Forwarder for all the VLANs for which it is appointed in either its Hello appointment database or its E-L1CS appointment database from the DRB if the VLAN is enabled and if the port is not configured as a trunk or IS-IS point-to-point port. If the receiver was Appointed Forwarder for any VLANs because they were in the Hello appointment database and they are no longer in the Hello appointment database, its Appointed Forwarder status for such VLANs is revoked. For example, if none of these sub-TLVs in a Hello D. Eastlake, et al [Page 10]
INTERNET-DRAFT TRILL: Appointed Forwarders appoints the receiving RBridge, then it loses all Appointed Forwarder status on the port where the Hello was received due to Hello appointment database entries but it retains Appointed Forwarder status due to E-L1CS FS-LSP appointments. The handling of one or more forwarder appointment 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). There is no reason for an RBridge to remember that it received a valid appointment Hello message for a VLAN that was ineffective because the VLAN was not enabled on the port where the Hello 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. The limitations due to the size of the Hello PDU make it desirable to use E-L1CS FS-LSPs for appointment. But if Hellos need to be used, due to TRILL switches on the link not supporting E-L1CS FS-LSPs, the remainder of this section gives a method to maximize the use of the limited space in Hellos for forwarder appointment. 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 that 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 an 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 D. Eastlake, et al [Page 11]
INTERNET-DRAFT TRILL: Appointed Forwarders 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. 2.2.2 Frequency of Hello Appointments Appointments made though E-L1CS FS-LSPs use the same IS-IS timing constants as for LSP flooding. The general IS-IS link state flooding mechanism is robust and includes acknowledgements so that it automatically recovers from lost PDUs, re-booted TRILL switches, and the like. For Hello appointments, it is not necessary for the DRB to include the Hello 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 in Section 3 but see also Section 4). It is also RECOMMENDED that the DRB have enabled all VLANs for which end station service will be offered on the link as well as the Designated VLAN. 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 in 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 Hello Limit The Hello 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 when E-L1CS FS-LSP appointments cannot be used due to the presence of legacy RBridges. To obtain a conservative estimate of this limit, 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 at the end of Section 2.2.1 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. And in any case such limitations D. Eastlake, et al [Page 12]
INTERNET-DRAFT TRILL: Appointed Forwarders are easily avoided by using E-L1CS FS-LSP appointment. 2.3 Local Configuration Actions 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 necessarily cause the RBridge to become an Appointed Forwarder for the link that port is on. However, such actions allow the port's RBridge to become Appointed Forwarder by choice if it is the DRB or, if it is not the DRB on the link, by appointment as indicated by the Hello or E-L1CS FS-LSP appointment databases. 2.4 Overload and Appointed Forwarders A TRILL switch in link state overload [rfc7180bis] will, in general, do a poorer job of ingressing and forwarding frames than a TRILL switch not in overload and that has full knowledge of the campus topology. For example, as explained in [rfc7180bis], an overloaded TRILL switch may not be able to distribute multi-destination TRILL Data frames at all. Therefore, the DRB SHOULD NOT appoint an RBridge in overload as an Appointed Forwarder. Furthermore, if an Appointed Forwarder becomes overloaded, the DRB SHOULD re-assign VLANs from the overloaded RBridge to another RBridge on the link that is not overloaded, if one is available. A counter-example would be if all campus end stations in VLAN-x were on links attached to RB1 via ports where VLAN-x was enabled. In such a case, RB1 SHOULD be made the VLAN-x Appointed Forwarder on all such links even if RB1 is overloaded. Overload does not affect DRB election but a TRILL switch in overload MAY reduce its own priority to be DRB. 2.5 VLAN Mapping within a Link TRILL Hellos include a field that is set to the VLAN in which they are sent when they are send on a link technology such as Ethernet D. Eastlake, et al [Page 13]
INTERNET-DRAFT TRILL: Appointed Forwarders that has outer VLAN labeling. (For link technologies such as PPP that do not have outer VLAN labeling, this Hello field is ignored.) If a TRILL Hello arrives on a different VLAN than it was sent on, then VLAN mapping is occurring within the link. 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 multi-destination frame would loop forever. Such a frame would be immortal. For a specific example, see Appendix C. 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 TRILL switch (possibly the DRB) is the Appointed Forwarder on the link for both VLAN-x and VLAN-y. D. Eastlake, et al [Page 14]
INTERNET-DRAFT TRILL: Appointed Forwarders 3. The Inhibition Mechanism A TRILL switch 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 Appendix A 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 the VLANs for which the RBridge is the Appointed Forwarder and one for all other VLANs. Thus, at least two VLAN inhibition 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 TRILL switch will not have had a chance yet to learn they are on the same link. 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 a TRILL switch 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 a TRILL switch decides that it has lost DRB status on a link, D. Eastlake, et al [Page 15]
INTERNET-DRAFT TRILL: Appointed Forwarders it sets the DRB inhibition timer to expired. Note: In the corner case where one port of a TRILL switch was the DRB election winner, but later lost the DRB election to a different port of the same TRILL switch on that link (perhaps due to management configuration of port priorities), neither 2 nor 3 above applies, and the DRB timer is not changed. 4. When a TRILL switch RB1 receives a TRILL Hello asserting that the sender is the Appointed Forwarder and that Hello 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. A TRILL switch MUST maintain VLAN inhibition timers covering 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 a TRILL switch 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. Remember, inhibition has no effect on TRILL Data or IS-IS packets, inhibition only affects native frames. 6. When a TRILL switch 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 TRILL switch is receiving Bridge PDU (BPDUs) on the port from an attached bridged LAN; if no BPDUs are being received, the root change inhibition timer will never be set. 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 is 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. Further optimizations are specified in Section 3.2. 7. When a TRILL switch 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 as the initial value of the merged timers. D. Eastlake, et al [Page 16]
INTERNET-DRAFT TRILL: Appointed Forwarders 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 TRILL switch has decided these ports connect. 3.1 Inhibited Appointed Forwarder Behavior Inhibition has no effect on the receipt or forwarding of TRILL Data packets or TRILL IS-IS packets. It only affects ingressing and egressing native frames. 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 covering VLAN-x is not expired. If a VLAN-x Appointed Forwarder for a link is inhibited and receives a TRILL Data packet whose encapsulated frame would normally be egressed to that link in VLAN-x, it decapsulates the native frame 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 TRILL switch with one or more unexpired inhibition timers, possibly including an unexpired inhibition timer covering 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. 3.2 Root Change Inhibition Optimizations The subsections below specify three optimizations that can reduce inhibition time of an RBridge port under certain circumstances for changes in the root Bridge ID being received by that port and thus decrease any transient interruption in end station service due to inhibition. TRILL switches MAY implement these optimizations. In the D. Eastlake, et al [Page 17]
INTERNET-DRAFT TRILL: Appointed Forwarders first two optimization, inhibition can be eliminated entirely under some circumstances. These optimizations are a bit heuristic in that with some unlikely multiple changes in a bridged LAN that occur simultaneously or nearly so the optimizations make transient looping more likely. 3.2.1 Change Optimization One Assume the root Bridge ID being received on an RBridge port changes to a new root Bridge ID with lower priority and a different root Bridge MAC address due to a single change in the bridged LAN. There are two possible reasons for this: (1) the bridged LAN to which the port is connected has partitioned due to link failure or otherwise, and the port is connected to a part that does not contain the original root bridge; (2) the original root bridge has been reconfigured to have a lower priority and a new root has taken over. Both of these are safe conditions that do not require inhibition. 3.2.2 Change Optimization Two Assume the root Bridge ID changes due to a single change in the bridged LAN but only the explicit priority portion of it changes. This means that the 48-bit MAC address portion is unchanged so the root bridge has been reconfigured to have a different priority but the same bridge is root and there has been no topology change. Thus, it is safe to ignore this sort of root Bridge ID change and not invoke the inhibition mechanism. 3.2.3 Settling Detection Optimization The dangerous case is the merger of bridged LANs that had been separate TRILL links in the same campus. In general, these links may have had different Appointed Forwarders on them for the same VLAN. Without inhibition, after the merger, you could have loops involving those VLANs. (Only native frames egressed and ingressed by RBridges are a potential problem. TRILL data packets are either individually addressed (TRILL Header M bit = 0) and will be ignored if delivered to any incorrect TRILL switch ports, or multicast (TRILL Header M bit = 1), in which case the Reverse Path Forwarding Check discards any copies delivered to incorrect TRILL switch ports. Thus there is no need for inhibition to affect sending or receiving TRILL data packets and inhibition does not do so.) D. Eastlake, et al [Page 18]
INTERNET-DRAFT TRILL: Appointed Forwarders However, root change inhibition is only needed until TRILL Hellos have been exchanged on the merged bridged LAN. Hellos indicate Appointed Forwarder status and, in general, after an exchange of Hellos the new merged bridged LAN link will, if necessary, be rendered TRILL loop safe by VLAN inhibition so that root change inhibition is not longer needed. TRILL switches are required to advertise in their link state the IDs of the root Bridge IDs they can see. If an RBridge port sees a change in root Bridge ID from Root1 to Root2, it is safe to terminate root bridge inhibition on that port as soon as Hellos have been received on the port from all RBridges that can see Root1 or Root2 except any such RBridge that is no longer reachable. In further detail, when a change from Root1 to Root2 is noticed at a port of RB1, RB1 associates with that port a list of all of the reachable RBridges, other than itself, that had reported in their LSP that they could see either Root1 or Root2. It then removes from this list any RBridge that becomes unreachable from RB1 or from which it has received a Hello on that port. If there is a subsequent change in root Bridge ID being received before this list is empty, say to Root7, then those RBridges reporting in their LSP that they can see Root7 are added to the list. Root bridge change inhibition can be terminated for the port as soon as either the timeout is reach or this list of RBridges is empty. If the optimizations in Sections 3.2.1 and/or 3.2.2 are in effect at an RBridge port and indicate that no inhibition is needed, then the mechanism in this section is not needed either. D. Eastlake, et al [Page 19]
INTERNET-DRAFT TRILL: Appointed Forwarders 4. Optional TRILL Hello Reduction If a network manager has sufficient confidence that they know the configuration of bridges, ports, and the like, within an Ethernet link, they may be able to reduce the number of TRILL Hellos sent on that link by sending Hellos in fewer VLANs; for example, if all TRILL switches on the link will see all Hellos without VLAN constraints. However, because adjacencies are established in the Designated VLAN, an RBridge MUST always attempt to send Hellos in the Designated VLAN. Hello reduction makes TRILL less robust in the face of decreased VLAN connectivity within a link, such as partitioned VLANs, VLANs disabled on ports, or disagreement over the Designated VLAN; however, as long as all RBridge ports on the link are configured for the same Desired Designated VLAN, can see each other's frames in that VLAN, and utilize the mechanisms specified below to update VLAN inhibition timers, operations will be safe. (These considerations do not arise on links between RBridges that are configured as point-to-point since, in that case, each RBridge sends point-to-point Hellos, other TRILL IS-IS PDUs, and TRILL Data frames only in what it believes to be the Designated VLAN of the link (although it may send them un- tagged) and no native frame end-station service is provided. Thus, for such links, there is no reason to send Hellos in any other VLAN than the Designated VLAN.) The provision for a configurable set of "Announcing VLANs", as described in Section 4.4.3 of [RFC6325], provides a mechanism in the TRILL base protocol for a reduction in TRILL Hellos. To maintain loop safety in the face of occasional lost frames, RBridge failures, link failures, new RBridges coming up on a link, and the like, the inhibition mechanism specified in Section 3 is still required. Strictly following Section 3, a VLAN inhibition timer can only be set by the receipt of a Hello sent or received in that VLAN. Thus, to safely send a reduced number of TRILL Hellos on a reduced number of VLANs requires additional mechanisms to set the VLAN inhibition timers at an RBridge, thus extending Section 3. Two such mechanisms are specified below. Support for both of these mechanisms is indicated by a capability bit in the PORT-TRILL-VER sub-TLV (Section 5.4 of [RFC7176]). It may be unsafe for an RBridge to send TRILL Hellos on fewer VLANs than the set of VLANs recommended in [RFC6325] on a link unless all its adjacencies on that link (excluding those in the Down state [RFC7177]) indicate support of these mechanisms and these mechanisms are in use. 1. An RBridge RB2 MAY include in any TRILL Hello an Appointed Forwarders sub-TLV [RFC7176] appointing itself for one or more ranges of VLANs. The Appointee Nickname field(s) in the Appointed Forwarder sub-TLV MUST be the same as the Sender Nickname in the Special VLANs and Flags sub-TLV in the TRILL Hellos sent by RB2. D. Eastlake, et al [Page 20]
INTERNET-DRAFT TRILL: Appointed Forwarders This indicates the sending RBridge believes it is Appointed Forwarder for those VLANs. An RBridge receiving such a sub-TLV sets each of its VLAN inhibition timers for every VLAN in the block or blocks listed in the Appointed Forwarders sub-TLV to the maximum of its current value and the Holding Time of the Hello containing the sub-TLV. This is backward compatible because such sub-TLVs will have no effect on any receiving RBridge not implementing this mechanism unless RB2, the sending RBridge, is the DRB (Designated RBridge) sending Hellos on the Designated VLAN, in which case RB2 MUST include in the Hello all forwarder appointments, if any, for RBridges other than itself on the link. 2. An RBridge MAY use the VLANs Appointed sub-TLV [RFC7176]. When RB1 receives a VLANs Appointed sub-TLV in a TRILL Hello from RB2 on any VLAN, RB1 updates the VLAN inhibition timers for all the VLANs that RB2 lists in that sub-TLV as VLANs for which RB2 is Appointed Forwarder. Each such timer is updated to the maximum of its current value and the Holding Time of the TRILL Hello containing the VLANs Appointed sub-TLV. This sub-TLV will be an unknown sub-TLV to RBridges not implementing it, and such RBridges will ignore it. Even if a TRILL Hello sent by the DRB on the Designated VLAN includes one or more VLANs Appointed sub- TLVs, as long as no Appointed Forwarders sub-TLVs appear, the Hello is not required to indicate all forwarder appointments. Two different encodings are provided above to optimize the listing of VLANs. Large blocks of contiguous VLANs are more efficiently encoded with the Appointed Forwarders sub-TLV, and scattered VLANs are more efficiently encoded with the VLANs Appointed sub-TLV. These encodings may be mixed in the same Hello. The use of these sub-TLVs does not affect the requirement that the "AF" bit in the Special VLANs and Flags sub-TLV MUST be set if the originating RBridge believes it is Appointed Forwarder for the VLAN in which the Hello is sent. If the above mechanisms are used on a link, then each RBridge on the link MUST send Hellos in one or more VLANs with such VLANs Appointed sub-TLV(s) and/or self-appointment Appointed Forwarders sub-TLV(s), and the "AF" bit is appropriately set such that no VLAN inhibition timer will improperly expire unless three or more Hellos are lost. For example, an RBridge could announce all VLANs for which it believes it is Appointed Forwarder in a Hello sent on the Designated VLAN three times per Holding Time. D. Eastlake, et al [Page 21]
INTERNET-DRAFT TRILL: Appointed Forwarders 5. Multiple Ports on the Same Link A TRILL switch may have multiple ports on the same link. Some of these ports may be suspended due to MAC address duplication as described in [RFC7177]. Suspended ports never ingress or egress native frames. If a TRILL switch 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 TRILL switch is eligible to be an Appointed Forwarder for that link. It can become Appointed Forwarder in the ways discussed in Section 2. If a TRILL switch 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 TRILL switch 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. D. Eastlake, et al [Page 22]
INTERNET-DRAFT TRILL: Appointed Forwarders 6. Port-Shutdown Messages A TRILL switch may note that one of its ports has failed or it may be about to shut down that port. If the port is on a link along with ports of other TRILL switches, those TRILL switches will not notice the port shutdown or failure using TRILL base protocol mechanisms until there is a failure to receive a number of Hellos from that port. This can take many seconds. Network topology (adjacencies) and forwarder appointments can react more rapidly to port shutdown or failure through explicit notification. As discussed below, this notification SHOULD be provided through the Port-Shutdown message. 6.1 Planned Shutdown and Hellos A TRILL switch that is shutting down one of its ports P1 soon SHOULD reduce its Holding Time on that port, so that the shutdown will be more rapidly noticed by adjacent RBridges that might not support the Port Shutdown message. 6.2 Port-Shutdown Message Structure The Port-Shutdown Message is an RBridge Channel Message [RFC7178] using RBridge Channel protocol number tbd5. The Channel Protocol specific payload consists of a list of Port IDs (see Section 4.4.2 of [RFC6325]) for the port or ports that have failed or are being shutdown as shown below. Support for the Port Shutdown message is advertised by simply advertising support for its RBridge Channel protocol in the RBridge Channel Protocols Sub-TLV [RFC7176]. D. Eastlake, et al [Page 23]
INTERNET-DRAFT TRILL: Appointed Forwarders 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 TRILL Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V |A|C|M| RESV |F| Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Egress Nickname | Ingress Nickname | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Special Inner.MacDA = All-Egress-RBridges | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Special Inner.MacDA cont. | Inner.MacSA | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Inner.MacSA cont. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VLAN Tag Ethertype=0x8100 | Priority=7, DEI=0, VLAN ID=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RBridge Channel Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RBridge-Chan. Ethertype=0x8946| CHV=0 | Channel Protocol=tbd5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | ERR=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Information specific to the Port-Shutdown Channel Protocol: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port ID 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port ID 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port ID K | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6.3 Port-Shutdown Message Transmission For robustness, a TRILL switch sends a number of copies of a Port- Shutdown messages configurable from one to three, which defaults to two copies, at a configurable interval, which defaults to 20 milliseconds (see Section 6.6). As with any adjacency critical message, the Port-Shutdown Message SHOULD be sent with highest priority 7 and SHOULD NOT be marked as drop eligible. If a failure of port P1 on RBridge RB2 is detected by RB2, then the Port-Shutdown message announcing this is sequentially unicast through the rest of the TRILL campus to all RBridges with which P1 had an adjacency and which are advertising support for the Port-Shutdown RBridge Channel protocol. If a port shutdown is planned within one second, then the TRILL D. Eastlake, et al [Page 24]
INTERNET-DRAFT TRILL: Appointed Forwarders switch ceases to send Hellos out the port being shut down and either (1) sends the Port-Shutdown message to RBridge ports on the link advertising support of the Port-Shutdown RBridge Channel protocol, or (2) broadcasts the Port-Shutdown message announcing this through the port as follows: - The Outer.MacDA is the All-RBridges multicast address. - If an outer VLAN tag is present, it specified the designated VLAN for the link, SHOULD specify priority 7, and SHOULD NOT specify drop eligible. - In the TRILL Header, the egress nickname is All-RBridges and the M bit in the TRILL Header set to 0. - In the RBridge Channel Header, the MH and NA bits are zero. There is no need for a special message to indicate that a port P1 has come back up or that a shutdown has been "cancelled". This is indicated by simply sending Hellos out port P1. 6.4 Port-Shutdown Message Reception When a TRILL switch RB1 receives a Port-Shutdown message RB1 checks that the ingress nickname specifies some TRILL switch RB2 with which RB1 has one or more adjacencies. If so, it drops those adjacencies that are to RB2 ports whose Port IDs are listed in the Port-Shutdown message. There could be more than one if RB2 had multiple ports on the link that are going down. If RB1 is DRB and this eliminates all adjacencies on a link between the DRB and RB2, then, for all VLANs whose ingress/egress was being handled by RB2, the DRB either starts acting an Appointed Forwarder or appoints some new TRILL switch with which it has adjacency as Appointed Forwarder. 6.5 Port-Shutdown Message Security Port-Shutdown messages can be secured through use of the Channel Tunnel security features [ChannelTunnel]. 6.6 Port-Shutdown Configuration There are two Port-Shutdown configuration parameters (see Section 6.3): D. Eastlake, et al [Page 25]
INTERNET-DRAFT TRILL: Appointed Forwarders Parameter Default Range --------- --------- ------- PShutdownRepeat 2 1-3 PShutdownDelay 20ms 0-1000 milliseconds D. Eastlake, et al [Page 26]
INTERNET-DRAFT TRILL: Appointed Forwarders 7. FGL-VLAN Mapping Consistency Checking TRILL switches support 24-bit Fine Grained Labels as specified in [RFC7172]. Basically a VLAN ID in native traffic between an edge TRILL switch and an end station is mapped from/to an FGL as an Inner.Label in TRILL Data packets. Since the Appointed Forwarder for a VLAN will be ingressing and egressing such native traffic, the mapping configured at the Appointed Forwarder is the mapping performed. However, the Appointed Forwarder for VLAN-x on a link can change for reasons discussed elsewhere in this document. Thus all TRILL switches on a link that are configured with a FGL-VLAN mapping SHOULD be configured with the same mapping. Otherwise traffic might unpredictably jump from one FGL to another when the Appointed Forwarder changes. TRILL switches SHOULD advertise their mapping on the link using the FGL-VLAN-Bitmap and FGL-VLAN-Pairs APPsub-TLVs (Sections 10.4 and 10.5) so that consistency checking can be automated. A TRILL switch SHOULD compare the FGL-VLAN mappings that it sees advertised by other TRILL switches on a link with its own and alert the network operator if they are inconsistent. Inconsistent means that (1) one TRILL switch maps FGL-z to VLAN-x while another maps FGL-z to VLAN-y or (2) one TRILL switch maps VLAN-x to FGL-w while another maps VLAN-x to FGL-z, all on the same link. Depending on how the network is being managed, a transient inconsistency may not be a problem. Thus the network operator SHOULD NOT be alerted unless the inconsistency persists for a period of time which defaults to the TRILL switch's Holding Time and is configurable to between zero and 2**16 - 1 seconds where 2**16 - 1 is a special value and indicates that such alerts are disabled. D. Eastlake, et al [Page 27]
INTERNET-DRAFT TRILL: Appointed Forwarders 8. Support of E-L1CS All TRILL switches MUST support the E-L1CS flooding scope [RFC7356], E-L1FS flooding scope [rfc7180bis], and base LSPs [IS-IS]. It will be apparent to any TRILL switch on a link if any other TRILL switch on the link is a legacy implementation not supporting E-L1CS because, as stated in [rfc7180bis], all TRILL switches MUST include a Scoped Flooding Support TLV [RFC7356] in all TRILL Hellos they send. This support of E-L1CS increases the amount of information from each TRILL switch that can be synchronized on the link, compared with the information capacity of Hellos, by several orders of magnitude. For robustness, E-L1CS PDUs (FS-LSP fragments, E-L1CS FS-CSNPs, and E-L1CS FS-PSNPs) MUST NOT exceed 1470 bytes in length; however, any such E-L1CS PDU that is received that is longer than 1470 bytes is processed normally. As with any type of IS-IS LSP, FS-LSPs are identified by the System ID of the originating router (TRILL switch) and the fragment number. In particular, there is no port identifier in the header of a E-L1CS PDU. Thus a TRILL switch RB1 with more than one non-suspended port on a link (Section 5) transmitting such a PDU MAY transmit it out any one or more of such ports. RB1 will generally receive such a PDU that other TRILL switches send on all of RB1's ports on the link. In addition, with multiple ports on the link, it will receive any such PDU that it sends on the ports it has on the link other than the transmitting port. 8.1 Backwards Compatibility Future TRILL specifications making use of E-L1CS MUST specify how situations involving a TRILL link will be handled when one or more TRILL switches attached to that link support E-L1CS and one or more do not. D. Eastlake, et al [Page 28]
INTERNET-DRAFT TRILL: Appointed Forwarders 9. 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 as described in Section 6 of [RFC6325]. The Port-Shutdown message specified in Section 6 SHOULD be secured through use of the Tunnel Channel protocol [ChannelTunnel]. These messages are build on the RBridge Channel feature whose security considerations are in [RFC7178]. The E-L1CS FS-LSPs added by Section 6 are securable with [RFC5310] Authentication TLVs in the same way as Hellos or other IS-IS PDUs. D. Eastlake, et al [Page 29]
INTERNET-DRAFT TRILL: Appointed Forwarders 10. Code Points and Data Structures This section provides IANA Considerations for this document and specifies the structure of the Appointment Bitmap, Appointment List, VLAN-FGL Mapping Bit Map, and VLAN-FGL Mapping Pairs APPsub-TLVs. These APPsub-TLVs appears within a TRILL GENINFO TLV [RFC7357] in E- L1CS FS-LSPs [RFC7356]. 10.1 IANA Considerations IANA is requested to assign four new APPsub-TLV type codes from the range below 255 and enter them in the "TRILL APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1" Registry as follows: Type Name Reference ---- ----------------- --------------- tbd1 AppointmentBitmap [this document] tbd2 AppointmentList [this document] tbd3 FGL-VLAN-Bitmap [this document] tbd4 FGL-VLAN-Pairs [this document] IANA is requested to assign a new RBridge Channel protocol number in the range assigned by Standards Action and update the "RBridge Channel Protocols" registry as follows: Protocol Description Reference -------- -------------- --------- tbd5 Port Shut-Down [this document] IANA is requested to update the reference for the "Hello reduction support" bit in the "PORT-TRILL-VER Sub-TLV Capability Flags" registry on the TRILL Parameters IANA web page to refer to this document. 10.2 Appointment Bitmap APPsub-TLV The Appointment Bitmap APPsub-TLV provides an efficient method for a TRILL switch to indicate which TRILL switches it appoints as forwarders for which VLAN IDs when those VLAN IDs are relatively compact, that is, they do not span a large numeric range. Such appointment is only effective when the appointing TRILL switch is DRB. D. Eastlake, et al [Page 30]
INTERNET-DRAFT TRILL: Appointed Forwarders 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Appointee Nickname | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | Starting VLAN ID | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bit Map ... (variable) +-+-+-+-+-+-+-+-... o Type: APPsub-TLV type, set to AppointmentBitmap sub-TLV tbd1. o Length: 4 + size of bit map in bytes. If Length is less than 4, the APPsub-TLV is corrupt and MUST be ignored. o Appointee Nickname: The nickname of the TRILL switch being appointed a forwarder. o RESV: 4 bits that MUST be sent as zero and ignored on receipt. o Starting VLAN ID: The smallest VLAN ID to which the bits in the Bit Map correspond. o Bit Map: A bit map of the VLANs for which the TRILL switch with appointee nickname is appointed the forwarder. The size of the bit map is length minus 4. If the size of the bit map is zero, no appointments are made. Each bit in the Bit Map corresponds to a VLAN ID. Bit 0 is for the VLAN whose ID appears in the Starting VLAN field. Bit 1 is for that VLAN ID plus 1 (treating VLAN IDs as unsigned integers) and so on with Bit N generally being Starting VLAN ID plus N. VLAN 0x000 and VLAN 0xFFF or any larger ID are invalid and are ignored. If the Appointment Bitmap APPsub-TLV is originated by the DRB on a link, it appoints the TRILL switch whose nickname appears in the Appointee Nickname field for the VLAN IDs corresponding to 1 bits in the Bit Map and revokes any Hello appointment of that TRILL switch for VLANs corresponding to 0 bits in the Bit Map. 10.3 Appointment List APPsub-TLV The Appointment List APPsub-TLV provides a convenient method for a TRILL switch to indicate which TRILL switches it appoints as D. Eastlake, et al [Page 31]
INTERNET-DRAFT TRILL: Appointed Forwarders forwarders for which VLAN IDs. Such appointment is only effective when the appointing TRILL switch is DRB. 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Appointee Nickname | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | VLAN ID 1 | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | VLAN ID 2 | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | VLAN ID k | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: APPsub-TLV type, set to AppointmentList sub-TLV tbd2. o Length: 2+2*k. If Length is not an even number, the APPsub-TLV is corrupt and MUST be ignored. o Appointee Nickname: The nickname of the TRILL switch being appointed a forwarder. o RESV: 4 bits that MUST be sent as zero and ignored on receipt. o VLAN ID: A 12-bit VLAN ID for which appointee is being appointed the forwarder. Type and Length are 2 bytes because these are extended FS-LSPs. This APPsub-TLV, when originated by the DRB, appoints the TRILL switch with Appointee Nickname to be the Appointed Forwarder for the VLAN IDs listed. 10.4 FGL-VLAN Mapping Bitmap APPsub-TLV The FGL-VLAN Mapping Bitmap APPsub-TLV provides a method for a TRILL switch to indicate the FGL to VLAN ID mappings it is configured to perform when egressing and ingressing native frames. The coding is efficient when the VLAN IDs are compact, that is, they do not span a large numeric range, and the FGLs and VLANs are paired in a monotonically increasing fashion. D. Eastlake, et al [Page 32]
INTERNET-DRAFT TRILL: Appointed Forwarders 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | Starting VLAN ID | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Starting FGL | (3 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Bit Map ... (variable) +-+-+-+-+-+-+-+-... o Type: APPsub-TLV type, set to VLAN-FGL-Bitmap sub-TLV tbd3. o Length: 5 + size of bit map in bytes. If Length is less than 5, the APPsub-TLV is corrupt and MUST be ignored. o RESV: 4 bits that MUST be sent as zero and ignored on receipt. o Starting VLAN ID: Initial VLAN ID for the mapping information as discussed below. o FGL: Fine Grained Label [RFC7172] o Bit Map: Map of bits for VLANs to FGL mappings. The size of the bit map is Length minus 5. If the size of the bit map is zero, no mappings are indicated. Each bit in the Bit Map corresponds to a VLAN ID and to an FGL. Bit 0 is for the VLAN whose ID appears in the Starting VLAN field and the Fine Grained Label that appears in the FGL field. Bit 1 is for that VLAN ID plus 1 and that FGL plus 1 (treating VLAN IDs and FGLs as unsigned integers) and so on with Bit N generally being Starting VLAN ID plus N and FGL plus N. If a Bit Map bit is a 1, it indicates that the advertising TRILL switch will map between the corresponding VLAN ID and FGL on ingressing native frames and egressing TRILL Data packets if it is Appointed Forwarder for the VLAN. If a Bit Map bit is a 0, it does not indicate any configured VLAN ID to FGL mapping. However, VLAN ID 0x000 and VLAN ID 0xFFF or any larger ID are invalid and FGLs larger than 0xFFFFFF are invalid; any Bit Map bits that corresponds to an illegal VLAN ID or illegal FGL is ignored. D. Eastlake, et al [Page 33]
INTERNET-DRAFT TRILL: Appointed Forwarders 10.5 FGL-VLAN Mapping Pairs APPsub-TLV The FGL-VLAN Mapping Pairs APPsub-TLV provides a method for a TRILL switch to indicate a list of FGL to VLAN ID mappings it is configured to perform when egressing and ingressing native frames. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=-+-...-+-+-+ | Mapping RECORD 1 | (5 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=-+-...-+-+-+ | Mapping RECORD 2 | (5 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=-+-...-+-+-+ | ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=-+-...-+-+-+ | Mapping RECORD k | (5 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-=-+-...-+-+-+ Where a Mapping RECORD has the following structure: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESV | VLAN ID | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FGL | (3 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ o Type: APPsub-TLV type, set to VLAN-FGL-Pairs sub-TLV tbd4. o Length: 5*k. If Length is not a multiple of 5, the APPsub-TLV is corrupt and MUST be ignored. o RESV: 4 bits that MUST be sent as zero and ignored on receipt. o VLAN ID: 12-bit VLAN label. o FGL: Fine Grained Label [RFC7172] Each Mapping RECORD indicates that the originating TRILL switch is configured to map between the FGL and VLAN given on egressing and ingressing native frames. However, VLAN ID 0x000 and VLAN ID 0xFFF are invalid; any Mapping RECORD that corresponds to an illegal VLAN ID is ignored. D. Eastlake, et al [Page 34]
INTERNET-DRAFT TRILL: Appointed Forwarders Normative References [802.1Q] - IEEE 802.1, "IEEE Standard for Local and metropolitan area networks - Virtual Bridged Local Area Networks", IEEE Std 802.1Q-2014, 19 December 2014. [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. [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC4971] - Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed., "Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information", RFC 4971, July 2007, <http://www.rfc-editor.org/info/rfc4971>. [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A. Ghanwani, "Routing Bridges (RBridges): Base Protocol Specification", RFC 6325, July 2011, <http://www.rfc- editor.org/info/rfc6325>. [RFC6329] - Fedyk, D., Ed., Ashwood-Smith, P., Ed., Allan, D., Bragg, A., and P. Unbehagen, "IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging", RFC 6329, April 2012, <http://www.rfc- editor.org/info/rfc6329>. [RFC7172] - Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and D. Dutt, "Transparent Interconnection of Lots of Links (TRILL): Fine-Grained Labeling", RFC 7172, May 2014, <http://www.rfc-editor.org/info/rfc7172>. [RFC7176] - Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt, D., and A. Banerjee, "Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS", RFC 7176, May 2014, <http://www.rfc-editor.org/info/rfc7176>. [RFC7177] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and V. Manral, "Transparent Interconnection of Lots of Links (TRILL): Adjacency", RFC 7177, May 2014, <http://www.rfc- editor.org/info/rfc7177>. [RFC7178] - Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D. Ward, "Transparent Interconnection of Lots of Links (TRILL): RBridge Channel Support", RFC 7178, May 2014, <http://www.rfc- editor.org/info/rfc7178>. D. Eastlake, et al [Page 35]
INTERNET-DRAFT TRILL: Appointed Forwarders [RFC7356] - Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding Scope Link State PDUs (LSPs)", RFC 7356, September 2014, <http://www.rfc-editor.org/info/rfc7356>. [RFC7357] - Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O. Stokes, "Transparent Interconnection of Lots of Links (TRILL): End Station Address Distribution Information (ESADI) Protocol", RFC 7357, September 2014, <http://www.rfc- editor.org/info/rfc7357>. [rfc7180bis] - Eastlake, D., Zhang, M., Perlman, R. Banerjee, A., Ghanwani, A., and S. Gupta, "TRILL: Clarifications, Corrections, and Updates", draft-ietf-trill-rfc7180bis, work in progress. Informative References [RFC5310] - Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, February 2009, <http://www.rfc-editor.org/info/rfc5310>. [RFC6439] - Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F. Hu, "Routing Bridges (RBridges): Appointed Forwarders", RFC 6439, November 2011, <http://www.rfc-editor.org/info/rfc6439>. [RFC7180] - Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and A. Banerjee, "Transparent Interconnection of Lots of Links (TRILL): Clarifications, Corrections, and Updates", RFC 7180, May 2014, <http://www.rfc-editor.org/info/rfc7180>. [RFC7379] - Li, Y., Hao, W., Perlman, R., Hudson, J., and H. Zhai, "Problem Statement and Goals for Active-Active Connection at the Transparent Interconnection of Lots of Links (TRILL) Edge", RFC 7379, October 2014, <http://www.rfc- editor.org/info/rfc7379> [ChannelTunnel] - D. Eastlake, M. Umair, Y. Li, draft-ietf-trill- channel-tunnel, work in progress. D. Eastlake, et al [Page 36]
INTERNET-DRAFT TRILL: Appointed Forwarders Acknowledgements The following are hereby thanked for their contributions to this document: Gayle Noble, Mingui Zhang The following were acknowledged and thanked by in [RFC6439] or were an author of [RFC6439], the predecessor to this document: Ron Bonica, Stewart Bryant, Linda Dunbar, Les Ginsberg, Erik Nordmark, Radia Perlman, Dan Romascanu, and Mike Shand. D. Eastlake, et al [Page 37]
INTERNET-DRAFT TRILL: Appointed Forwarders Authors' Addresses 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 Mohammed Umair IPinfusion EMail: mohammed.umair2@ipinfusion.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.cn D. Eastlake, et al [Page 38]
INTERNET-DRAFT TRILL: Appointed Forwarders Appendix A: 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 for 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. D. Eastlake, et al [Page 39]
INTERNET-DRAFT TRILL: Appointed Forwarders Appendix B: Changes to RFCs 6325, 6439, 7177 This document updates [RFC6325], obsoletes [RFC6439], and updates [RFC7177]. Change to [RFC6325], the TRILL base protocol, is as follows: Addition of mandatory support for E-L1CS FS-LSPs. Changes from [RFC6439], which this document obsoletes, are as follows: 1. Specify APPsub-TLVs and procedures to be used in E-L1CS FS-LSP forwarder appointments. 2. Incorporate updates to [RFC6439] that appeared in Section 10 of [RFC7180] which has been obsoleted by [rfc7180bis]. They appear primarily in Section 4 of this document. 3. Add optional FGL-VLAN consistency check feature including specification of APPsub-TLVs. 4. Delete references to draft-ietf-trill-rbridge-vlan-mapping which has been dropped by the TRILL WG. 5. Addition of the Port Shutdown message. 6. Eliminate requirement that the DRB not send appointments in Hellos until its DRB inhibition timer has expired. This was an unnecessary safety precaution that is pointless given that appointments in E-L1CS FS-LSPs are immediately visible. 7. Addition of three optional methods to optimize (reduce) inhibition time under various circumstances. 8. Editorial changes. Changes to [RFC7177] are as follows: As provided in Section 6, TRILL switches SHOULD treat the reception of a Port-Shutdown RBridge Channel message from RB1 listing port P1 as if it were an event A3 as specified in [RFC7177] resulting in transition of any adjacency to P1 to the Detect state. D. Eastlake, et al [Page 40]
INTERNET-DRAFT TRILL: Appointed Forwarders Appendix C: Multi-Link VLAN Mapping Loop Example Assume that RBridges RB1 and RB2 have ports P1 and P2, respectively, that are both on link L1 and that RBridges RB3 and RB4 have ports P3 and P4, respectively, that are both on Link L2. Assume further that P1 and P3 are Appointed Forwarder for VLAN-x and P2 and P4 are Appointed Forwarder for VLAN-y. This situation is shown in the figure below. + - - - - - - - - - - - - - - - - - - - - - + | | | TRILL network | | | | +---+ +---+ +---+ +---+ | + -|RB1|- -|RB2|- - - - - - -|RB3|- -|RB4|- + +---+ +---+ +---+ +---+ P1| P2| P3| P4| | | | | |x |y |x |y | +-+ | | +-+ | L1 ---+---|M|---+--+--- L2 ---+---|M|---+--- +-+ | +-+ +---+ |ES1| +---+ Further assume L1 and L2 are each bridged LANs that include a device M, presumably a bridge, that maps VLAN-x into VLAN-y and VLAN-y into VLAN-x. If end station ES1 originated a broadcast or other multi-destination frame in VLAN-y, it would be ingressed by RB2. (The frame would also be mapped to VLAN-x and ingressed by RB1 but we initially ignore that.) RB2 will flood the resulting TRILL Data packet through the campus and, at least in the broadcast and unknown unicast cases, it will get to RB4 where it will be egressed to L2. Inside L2, this broadcast frame is mapped to VLAN-x and then ingressed by RB3. RB3 then floods the resulting TRILL Data packet through the campus, this time with an Inner.VLAN of VLAN-x, as a result of which it will be egressed by RB1 into L1. Inside L1, it will be mapped back to VLAN-y and then ingressed by RB2 completing the loop. The packet will loop indefinitely, because in native form on L1 and L2 it has no TRILL hop count, and an indefinitely large number of copies will be delivered to ES1 and any other end station so situated. The same problem would occur even if P1 and P2 were on the same RBridge and/or P3 and P4 were on the same RBridge. Actually, because the original frame was also mapped to VLAN-x inside L1 and ingressed by RB1, there are two copies looping around in opposite directions. The use of Fine Grained Labels [RFC7172] complicates but does not D. Eastlake, et al [Page 41]
INTERNET-DRAFT TRILL: Appointed Forwarders essentially change the potential problem. This example shows why VLAN mapping between Appointed Forwarder ports on a TRILL link is loop unsafe. When such a situation is detected, the DRB on the link changes Appointed Forwarders as necessary to assure that a single RBridge port is Appointed Forwarder for all VLANs involved in mapping. This change makes the situation loop safe. D. Eastlake, et al [Page 42]
INTERNET-DRAFT TRILL: Appointed Forwarders Appendix Z: Change Record This appendix summarizes changes between versions of this draft. RFC Editor: Please delete this Appendix before publication. Initial WG version -00 From -00 to -01 Primarily editorial changes based on review by Gayle Noble. D. Eastlake, et al [Page 43]
INTERNET-DRAFT TRILL: Appointed Forwarders Copyright and IPR Provisions Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 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. The definitive version of an IETF Document is that published by, or under the auspices of, the IETF. Versions of IETF Documents that are published by third parties, including those that are translated into other languages, should not be considered to be definitive versions of IETF Documents. The definitive version of these Legal Provisions is that published by, or under the auspices of, the IETF. Versions of these Legal Provisions that are published by third parties, including those that are translated into other languages, should not be considered to be definitive versions of these Legal Provisions. For the avoidance of doubt, each Contributor to the IETF Standards Process licenses each Contribution that he or she makes as part of the IETF Standards Process to the IETF Trust pursuant to the provisions of RFC 5378. No language to the contrary, or terms, conditions or rights that differ from or are inconsistent with the rights and licenses granted under RFC 5378, shall have any effect and shall be null and void, whether published or posted by such Contributor, or included with or in such Contribution. D. Eastlake, et al [Page 44]