Fast Connectivity Restoration Using BGP Add-path
Author(s): Rex Fernando, Robert Raszuk, Pradosh Mohapatra, Clarence Filsfils
A BGP route defines an association of an address prefix with an 'exit point' from the current Autonomous System (AS). If the exit point becomes unreachable due to a failure, the route becomes invalid. This usually triggers an...
Network Working Group P. Mohapatra Internet-Draft R. Fernando Intended status: Standards Track C. Filsfils Expires: July 26, 2013 Cisco Systems R. Raszuk NTT MCL Inc. January 22, 2013 Fast Connectivity Restoration Using BGP Add-path draft-pmohapat-idr-fast-conn-restore-03 Abstract A BGP route defines an association of an address prefix with an "exit point" from the current Autonomous System (AS). If the exit point becomes unreachable due to a failure, the route becomes invalid. This usually triggers an exchange of BGP control messages after which a new BGP route for the given prefix is installed. However, connectivity can be restored more quickly if the router maintains precomputed BGP backup routes. It can then switch to a backup route immediately upon learning that an exit point is unreachable, without needing to wait for the BGP control messages exchange. This document specifies the procedures to be used by BGP to maintain and distribute the precomputed backup routes. Maintaining these additional routes is also useful in promoting load balancing, performing maintenance without causing traffic loss, and in reducing churn in the BGP control plane. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on July 26, 2013. Copyright Notice Mohapatra, et al. Expires July 26, 2013 [Page 1] Internet-Draft Fast Connectivity Restoration January 2013 Copyright (c) 2013 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. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Mohapatra, et al. Expires July 26, 2013 [Page 2] Internet-Draft Fast Connectivity Restoration January 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5 2. Basic Idea . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Design Considerations . . . . . . . . . . . . . . . . . . . . 6 3.1. Ensuring Loop-Free Path Selection in an AS . . . . . . . . 6 3.1.1. Border routers announcing single path . . . . . . . . 6 3.1.2. Border routers announcing multiple paths . . . . . . . 7 3.1.3. Confederations . . . . . . . . . . . . . . . . . . . . 7 3.2. Keeping Path Attributes Independent of Decision Process . 8 4. Edge_Discriminator attribute . . . . . . . . . . . . . . . . . 8 5. Calculation of Best and Backup Paths . . . . . . . . . . . . . 9 6. Advertising Multiple Paths . . . . . . . . . . . . . . . . . . 13 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 13 8. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.1. Fast Connectivity Restoration . . . . . . . . . . . . . . 14 8.2. Load Balancing . . . . . . . . . . . . . . . . . . . . . . 14 8.3. Churn Reduction . . . . . . . . . . . . . . . . . . . . . 15 8.3.1. Inter-domain Churn Reduction . . . . . . . . . . . . . 15 8.3.2. Intra-Domain Churn Reduction . . . . . . . . . . . . . 15 8.4. Graceful Maintenance . . . . . . . . . . . . . . . . . . . 17 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 11. Security Considerations . . . . . . . . . . . . . . . . . . . 17 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 12.1. Normative References . . . . . . . . . . . . . . . . . . . 18 12.2. Informative References . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Mohapatra, et al. Expires July 26, 2013 [Page 3] Internet-Draft Fast Connectivity Restoration January 2013 1. Introduction Within an autonomous system, the availability of multiple routes to a given destination, where each of the routes has a different "exit point" from the local AS provides the following benefits: o Fault tolerance: Knowledge of multiple "exit points" leads to reduction in restoration time after failure. For instance, a border router on receiving multiple paths to the same destination could decide to precompute a backup path and have it ready so that when the primary path becomes invalid, it could use the backup to quickly restore connectivity. Currently the restoration time is dependent on BGP protocol re-convergence that includes a set of withdraw and advertisement messages in the network before a new best path can be learnt. o Load balancing: The availability of multiple paths to reach the same destination enables load balancing of traffic provided the paths for the given destination satisfy certain constraints. o Churn reduction: The advertisement of multiple routes, in certain scenarios (Section 8.3.2), could lead to less churn in the network upon a failure, since the presence of multiple paths helps contain the failure to the local AS where the failure occurs. o Graceful maintenance: The availability of alternate exit points allows one to bring down a router for maintenance without causing significant traffic loss. Unfortunately, the border routers in an AS do not receive multiple paths for all prefixes. The reason is three-fold: o The current BGP specification [RFC4271] specifies routers to advertise only the best path for a destination to speakers. The availability of multiple paths requires simultaneous distribution of multiple routes for a given prefix by a BGP speaker. We refer to this property of the network as "path diversity". o When a router selects an IBGP learnt path as best, it does not announce any path for that prefix to IBGP though it may have EBGP learnt paths available. This loss of information leads to added churn and increases convergence time if the preferred path goes away. A mechanism to advertise the best-external path to IBGP is proposed in [I-D.ietf-idr-best-external]. o Most service providers deploy one of the scaling techniques like route reflectors [RFC4456] or confederations[RFC5065] inside the AS and avoid iBGP full mesh. Thus even when multiple paths exist, Mohapatra, et al. Expires July 26, 2013 [Page 4] Internet-Draft Fast Connectivity Restoration January 2013 the aggregation points (route reflectors or confederation border routers) advertise only the best path (as per the BGP base protocol). As an effect of this behavior, the ingress border routers to an AS do not receive additional paths necessary to provide the benefits cited above: e.g. perform a local recovery during network failures or achieve load balancing in steady state across multiple exit points. The mechanism to extend BGP to allow a given BGP speaker to advertise multiple paths simultaneously for a destination is defined in [I-D.ietf-idr-add-paths]. The current draft describes the use of this generic technique and certain additional procedures and implementation guidelines to enable the above applications. More specifically, this document describes extensions to BGP decision process to select backup paths in a manner that ensures the important property of consistent route selection within an AS. It also introduces a new BGP attribute, Edge_Discriminator, that border routers should use to advertise multiple EBGP learnt paths for a given destination. To aid with better description of the applications, the draft illustrates certain use case scenarios for each. One implication of multiple path advertisement is the associated cost, namely the performance overhead of processing and memory overhead of storing additional paths. It is anticipated that the benefits listed above outweigh the cost in most scenarios. Be that as it may, it is also expected that there will be configuration knobs provided to limit the number of additional paths propagated within an AS. 1.1. Requirements Language 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 [RFC2119]. 2. Basic Idea This document proposes two main additions to the BGP procedures: 1. The decision process is modified to determine backup paths along with the best path selection when multiple paths for a destination are available. Mohapatra, et al. Expires July 26, 2013 [Page 5] Internet-Draft Fast Connectivity Restoration January 2013 2. In addition to using these backup paths for fast connectivity restoration locally, BGP speakers also advertise these paths to IBGP to increase the overall path diversity. As alluded to in Section 1, BGP speakers that are the aggregation points (router reflectors or confederation border routers) need to announce backup paths to increase the path diversity at the ingress routers of an IBGP network (see Figure 2). It may also be useful, in certain cases, for the border routers to advertise multiple paths received via EBGP for a destination when it is redundantly connected and is transparently passing the NEXT_HOP field unchanged instead of setting it to self (see Figure 4). To this end, the draft defines a new attribute, Edge_Discriminator, that the border routers should advertise to ensure path selection consistency. The following sections elaborate on these points. 3. Design Considerations 3.1. Ensuring Loop-Free Path Selection in an AS It is critical that BGP speakers within an AS have an eventual consistent routing view of destinations and do not make conflicting decisions regarding best path selection that would otherwise cause forwarding loops. The current BGP protocol ensures this property by defining a decision process that takes the attributes of paths as input and determines a degree of preference of the paths by applying a constant function. A consistent view of attributes is disseminated through IBGP. Thus each BGP speaker within the AS determines the same degree of preference of the paths after applying the constant function independently. (The one exception is where IGP metric plays the tie breaking role. In this case, different routers may choose different next hops that are closer to them; but loop freedom is guaranteed.). When the above mechanism is extended to select backup paths for the applications cited in this document, it is equally important to maintain the same consistency property for the backup paths, i.e. there should be no loops created when routers use the backup path in forwarding. The rest of the document goes into the details of this for various scenarios. 3.1.1. Border routers announcing single path In scenarios where all border routers advertise a single external path (their best path or best-external path) into IBGP, a consistent Mohapatra, et al. Expires July 26, 2013 [Page 6] Internet-Draft Fast Connectivity Restoration January 2013 routing view of best path and backup paths can be created across the AS with the current BGP selection rules. 3.1.2. Border routers announcing multiple paths There are scenarios where border routers need to advertise the best and backup EBGP learnt paths with NEXT_HOP unchanged to IBGP. If the border router sets next hop to self, the paths become indistinguishable and hence advertisement of only the best path is sufficient. An example scenario is depicted in Figure 4. By using the add-path ([I-D.ietf-idr-add-paths]) extensions, the border routers could advertise multiple such EBGP-learnt paths. But doing so can potentially create an inconsistency between the paths that the sending and receiving routers select for forwarding. In other words, the routers in the IBGP mesh can make independent and separate decisions on the route selection since some of the values that play a role in the tie breaking steps of the decision process at the sender are not available to the rest of the BGP speakers of the AS. These are mainly (1) the interior cost, i.e. the metric to reach the external next hop, (2) BGP identifier of the peer, (3) the peer IP address. Due to this reduction in information, there can be inconsistency in the routing view within an AS. Additionally, [RFC5004] proposes an extension to avoid best path transitions at the border router between external paths based on a temporal order of receiving the paths. This can also create an inconsistency across the BGP speakers in the path selection. This document proposes two modifications to ensure consistency: a. Border routers SHOULD not apply the modification to the selection rules as proposed in [RFC5004] to avoid best path transitions for parallel EBGP connection scenario where the border router wishes to transitively transmit the NEXT_HOP value unchanged. b. To overcome the "information reduction" problem described above, the document specifies an attribute called "Edge_Discriminator attribute" that encodes the properties of each path advertised that would otherwise not be included using the normal attributes in a BGP UPDATE message (see Section 4). 3.1.3. Confederations When an AS employs confederations and the confederation border routers advertise multiple paths, there is no way to distinguish the originator (the actual egress border router originating the prefix to the AS). To ensure consistent path selection, the confederation Mohapatra, et al. Expires July 26, 2013 [Page 7] Internet-Draft Fast Connectivity Restoration January 2013 border routers should create the ORIGINATOR_ID attribute as described in [RFC4456] that carries the BGP identifier of the originator of the route to the local AS. 3.2. Keeping Path Attributes Independent of Decision Process In addition to providing consistency in path selection, the solution should satisfy the following important property: the attributes associated with a particular path should be invariant when a different path is advertised or withdrawn. Other things being equal, it is best to avoid the potential churn introduced by the feedback loops that would occur if path attributes were changed at the sender as a result of running the decision process. Thus we do not use any attributes with semantics like "this is my second best path", "this is my third best path", etc. This requirement precludes use of marking or other means of indicating path ordering from sender's perspective since a change in the ordering requires re-advertising most of the paths. 4. Edge_Discriminator attribute Edge_Discriminator attribute is an optional non-transitive attribute that is composed of a set of Type-Length-Value (TLVs) encodings. The type code of the attribute is to be assigned by IANA. Each TLV contains an attribute of the path from the border router that is not otherwise sent as part of the UPDATE message. The TLV is structured as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attr Type | Length | | (1 octet) | (1 octet) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Value | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Edge_Discriminator attribute format a. Attr Type (1 octet): It identifies the type of the attribute that is encoded by the border router. Unknown types are to be ignored and skipped upon receipt. This document defines the following types: Mohapatra, et al. Expires July 26, 2013 [Page 8] Internet-Draft Fast Connectivity Restoration January 2013 * Interior Cost: Attr Type = 1 * peer BGP Identifier: Attr Type = 2 * IPv4 Peer Address: Attr Type = 3 * IPv6 Peer Address: Attr Type = 4 b. Length (1 octet): the total number of octets of the Value field. c. Value (variable): The value field encodes the attribute of the corresponding type. For "Interior Cost" type, it encodes the four octet metric value. For "BGP Identifier" type, it encodes the four-octet router identifier of the neighbor for the path. For "IPv4 Peering Address" type, the 4 byte BGP IPv4 peering address is encoded. For "IPv6 Peering Address" type, the 16 byte BGP IPv6 peering address is encoded. A brief description of how a BGP speaker constructs the attribute is provided in Section 6. 5. Calculation of Best and Backup Paths Mohapatra, et al. Expires July 26, 2013 [Page 9] Internet-Draft Fast Connectivity Restoration January 2013 /----------------------------------------\ | +----+ IBGP | | r1 | | +----+ | . | . | . | +----+ | | RR | | . +----+ . | . . | . . | +----+ +----+ | | r3 | | r4 | | +----+ +----+ | | | | \ | P1 | P2 / ---------------------------------------- | | EBGP | | EBGP ............... / \ Destination a \ / ............... Figure 2: Basic RR topology Mohapatra, et al. Expires July 26, 2013 [Page 10] Internet-Draft Fast Connectivity Restoration January 2013 /----------------------------------------\ | | +----+ +----+ | | r1 |...........| r2 | | +----+ +----+ | . . | . AS 65502 . | . . | . +----+ . | .....|CBR2|....... | +----+ | | | | CONFED EBGP | +----+ | .....|CBR1|....... | . +----+ . | . . | . AS 65501 . | . . | +----+ +----+ | | r3 |...........| r4 | | +----+ +----+ | |P1 |P2 | | | | ---------------------------------------- | | EBGP | | EBGP ............... / \ Destination a \ / ............... Figure 3: Confederation topology Mohapatra, et al. Expires July 26, 2013 [Page 11] Internet-Draft Fast Connectivity Restoration January 2013 /----------------------------------------\ | +----+ IBGP | | r1 | | +----+ | . | . | . | +----+ | | RR | | . +----+ . | . . | . . | +----+ +----+ | | r3 | | r4 | | +----+ +----+ | | | | \ P1| |P2 / ---------------------------------------- | | EBGP| |EBGP ............... / \ Destination a \ / ............... Figure 4: Border router with parallel eBGP links The decision process as described in [RFC4271] is followed to determine the overall best path for a destination. In addition, the following rule SHOULD be inserted into the tie breaking rules of the BGP decision process after step f) (Sect. 22.214.171.124: [RFC4271]) and after the CLUSTER_LIST length check step (Sect. 9: [RFC4456]): a BGP speaker SHOULD apply the tie breaking steps (steps (e), (f), and (g) as defined in [RFC4271]) with the values encoded in the Edge_Discriminator attribute. Note that the above step effectively compares multiple paths that are advertised by the same egress border router (since the BGP Identifier comparison step earlier would have eliminated paths from different egress border routers). Consider the network in Figure 4. r3 learns two paths P1 and P2 for destination a and wishes to advertise both to the iBGP mesh with NEXT_HOP value unchanged. We need to ensure that both r3 and the other ingress routers in the network (r1, r4) make a consistent route Mohapatra, et al. Expires July 26, 2013 [Page 12] Internet-Draft Fast Connectivity Restoration January 2013 selection for the best and the backup paths for destination a. The current tie breaking rules [step f) comparison of router ID or ORIGINATOR_ID and step g) comparision of peering ID] are insufficient since at the ingress routers, both the paths will be received with same values for each of the above parameters. Hence an additional tie breaking rule comparing the original values that the border router itself used to tie break the paths is required. Once the best path is chosen, eliminate that path and all paths that have the same BGP Identifier or NEXT_HOP as the choosen best path. Note that as specified in [RFC4456], if the path carries the ORIGINATOR_ID attribute, that should be treated as the BGP Identifier. Then rerun the best path procedure to choose the backup path. The Tie Breaking rules of the BGP decision process for second best path selection are also modified as described above. This mechanism can be recursively used to calculate multiple backup paths if desired. 6. Advertising Multiple Paths The technique outlined in [I-D.ietf-idr-add-paths] is used to advertise best and backup paths selected with the rules described in Section 5. For the purposes of the applications cited in this document, the "Path Identifier" is always treated as an opaque value with no semantics. When an egress border router chooses to advertise multiple paths learnt via EBGP to IBGP, it SHOULD include the Edge_Discriminator attribute as defined in Section 4 for each of the paths. The attribute is constructed by encoding the following properties of the path in TLV format: o The interior cost to reach the NEXT_HOP of the path, encoded with type 1. o The BGP identifier of the EBGP peer from which it received the path, encoded with type 2. o The peer address of the EBGP peer from which it received the path, encoded either with type 3 or 4. 7. Deployment Considerations To ensure consistency in path selection process across all the routers in an AS, the deployment considerations from the individual Mohapatra, et al. Expires July 26, 2013 [Page 13] Internet-Draft Fast Connectivity Restoration January 2013 scaling technology employed in the network should be inherited/ applied. For example, as specified in [RFC4456], the intra-cluster IGP metric values should be better than the inter-cluster IGP metric values. Similar considerations as specified in [RFC5065] should be designed. 8. Applications 8.1. Fast Connectivity Restoration Consider the network in Figure 2. All 4 routers indicated are part of a single AS. r3 and r4 are the border routers. Suppose r3 and r4 receive paths P1 and P2 for the same prefix. Also assume that P1 is the preferred exit. There are two scenarios to consider: case 1: P1 is the preferred exit for all routers within the AS (including r4). In this case, if r4 follows [RFC4271], r4 withdraws P2 from the IBGP cloud. case 2: P2 is preferred exit by r4. In this case, if RR follows [RFC4271], RR gets both paths, chooses one and sends it to r1. In both the cases above, 'r1' holds only a single path and only after a failure that makes P1 unavailable, it receives the alternate path (P2). However, if both paths were available to 'r1' and all other border routers in the network, then they could precompute backup paths and keep them ready to restore connectivity upon being notified of a failure. The failure notification could be triggered due to a link failure between 'r3' and its EBGP neighbor. This failure could be propagated to other routers in r3's AS either via IGP or BGP, resulting in invalidating on all these routers their primary paths that were advertised by that neighbor to r3 (and that r3 subsequently re-advertised into IBGP). Once these paths are invalidated, all these routers could switch to the precomputed backup paths, without waiting for any additional BGP advertisements. 8.2. Load Balancing In the above network, not only can the additional path be used as a standby best, but can also be used in steady state to load balance traffic across the two exit points. Mohapatra, et al. Expires July 26, 2013 [Page 14] Internet-Draft Fast Connectivity Restoration January 2013 8.3. Churn Reduction There are two aspects to reducing churn - Inter-domain and Intra- domain. 8.3.1. Inter-domain Churn Reduction Consider the network diagram in Figure 5. +----+ | r5 | +----+ | EBGP ------------- | +----+ | r1 | +----+ . . . . +----+ +----+ | r3 | | r4 | +----+ +----+ | P1 | P2 Figure 5 'r5' is an EBGP peer of 'r1'. Today, if path P1 goes away, due to the non-availability of other paths, 'r1' sends a withdraw to r5 thus triggering a churn in the Internet. This could be significant if there are multiple prefixes involved. On the other hand, if r1 had an alternate path (with identical attributes), then this churn could be entirely avoided by r1 performing a local repair. 8.3.2. Intra-Domain Churn Reduction Since advertising multiple paths in general increases the path diversity at the border routers, some of the control plane churn in terms of a stream of advertisements, withdraws, and re-advertisements can be reduced, thus improving the stability of the network. Mohapatra, et al. Expires July 26, 2013 [Page 15] Internet-Draft Fast Connectivity Restoration January 2013 AS 2 | | +----+ +----+ | r1 | | r2 | +----+ +----+ . . . . . . +----+ | RR | . +----+ . . . . . +----+ +----+ | r3 | | r4 | +----+ +----+ \ / \ / eBGP dual-homing AS 1(a) Figure 6 Assuming router r3's path is the best path in the AS, RR advertises the corresponding route information to the iBGP network. If r3 goes down (or the peering link [r3, AS1] fails and r3 didn't change the next hop to itself), the following will be sequence of updates from router r1 to AS 2: o Initial update for all prefixes when r1 chooses best path, o Withdraws for all prefixes when r1 detects failure, o Re-advertisement of all prefixes when the RR chooses router r4's path as the new best path and advertises to r1. With both the paths advertised and received on router r1, the sequence of updates reduces to: o Initial update for all prefixes when r1 chooses best path, o Re-advertisement of all prefixes when r1 detects failure and chooses router r4's path as the new best path Mohapatra, et al. Expires July 26, 2013 [Page 16] Internet-Draft Fast Connectivity Restoration January 2013 8.4. Graceful Maintenance [RFC6198] defines requirements for graceful maintenance of routers in a service provider network. Current BGP operations treat this as a sudden link or node failure and try to reconverge that can take in the order of seconds or minutes. With the procedures defined in this document, since alternate paths are available at the ingress routers, taking down egress routers from the network does not result in a network-wide reconvergence event. 9. Acknowledgements The authors would like to thank Enke Chen for the many discussions resulting in this work. In addition, the authors would also like to acknowledge valuable review and suggestions from Eric Rosen, Yakov Rekhter, and John Scudder on this document. 10. IANA Considerations This document defines a new BGP optional non-transitive attribute type, called Edge_Discriminator attribute. The attribute type is to be assigned by IANA. This document introduces Attr TLVs within the above attribute. The type space for these should be set up by IANA as a registry of 1-octet attr types. These should be assigned on a first-come-first- serve basis. This document defines the following attr types that should be assigned in the registry: Attr Type --------------- ----- Interior Cost 1 Peer BGP Identifier 2 IPv4 Peer Address 3 IPv6 Peer Address 4 11. Security Considerations There are no additional security risks introduced by this design. 12. References Mohapatra, et al. Expires July 26, 2013 [Page 17] Internet-Draft Fast Connectivity Restoration January 2013 12.1. Normative References [I-D.ietf-idr-add-paths] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", draft-ietf-idr-add-paths-08 (work in progress), December 2012. [I-D.ietf-idr-best-external] Marques, P., Fernando, R., Chen, E., Mohapatra, P., and H. Gredler, "Advertisement of the best external route in BGP", draft-ietf-idr-best-external-05 (work in progress), January 2012. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, March 1997. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC4271, January 2006. [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC4456, April 2006. [RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous System Confederations for BGP", RFC5065, August 2007. [RFC6198] Decraene, B., Francois, P., Pelsser, C., Ahmad, Z., Elizondo Armengol, A., and T. Takeda, "Requirements for the Graceful Shutdown of BGP Sessions", RFC6198, April 2011. 12.2. Informative References [RFC5004] Chen, E. and S. Sangli, "Avoid BGP Best Path Transitions from One External to Another", RFC5004, September 2007. Authors' Addresses Pradosh Mohapatra Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA Email: email@example.com Mohapatra, et al. Expires July 26, 2013 [Page 18] Internet-Draft Fast Connectivity Restoration January 2013 Rex Fernando Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA Email: firstname.lastname@example.org Clarence Filsfils Cisco Systems Brussels, Belgium Email: email@example.com Robert Raszuk NTT MCL Inc. 101 S Ellsworth Avenue Suite 350 San Mateo, CA 94401 USA Email: firstname.lastname@example.org Mohapatra, et al. Expires July 26, 2013 [Page 19]