Network Working Group A. Bashandy Internet Draft N. Kumar Intended status: Standards Track M. Konstantynowicz Expires: January 2013 Cisco Systems July 7, 2012 BGP FRR Protection against Edge Node Failure Using Vector Labels draft-bashandy-bgp-frr-vector-label-00.txt Abstract Consider a BGP free core scenario. Suppose the edge BGP speakers PE1, PE2,..., PEn know about a prefix P/m via the external routers CE1, CE2,..., CEm. If the edge router PEi crashes or becomes totally disconnected from the core, it is desirable for a core router "P" carrying traffic to the failed edge router PEi to immediately restore traffic by re-tunneling packets originally tunneled to PEi and destined to the prefix P/m to one of the other edge routers that advertised P/m, say PEj, until BGP re-converges. In doing so, it is highly desirable to keep the core BGP-free while not imposing restrictions on external connectivity or complicating provisioning effort. Thus (1) a core router should not be required to learn any BGP prefix, (2) the size of the forwarding and routing tables in the core routers should be independent of the number of BGP prefixes, (3) re-routing traffic without waiting for re-convergence must not cause loops, (4) provisioning effort should be kept at minimum, and (5) there should be no restrictions on what edge routers advertise what prefixes. For labeled prefixes, (6) the label stack on the packet must allow the repair PEj to correctly forward the packet and (7) there must not be any need to perform more than one label lookup on any edge or core router during steady state Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. 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Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................3 1.1. Conventions used in this document.........................5 1.2. Terminology...............................................5 1.3. Problem definition........................................7 2. Overview of BGP FRR in an MPLS Core............................8 2.1. Control Plane operation...................................8 2.2. Forwarding behavior at Steady State (while pPE is reachable) ..............................................................12 2.3. Forwarding behavior when pPE Fails.......................13 3. Overview of the BGP FRR using Vector Labels in an IP Core.....14 3.1. Pure IP Core.............................................15 Bashandy Expires January 7, 2013 [Page 2] Internet-Draft BGP FRR Using Vector Labels July 2012 3.1.1. Control Plane.......................................15 3.1.2. Forwarding plane during Steady State (when pPE is reachable).................................................15 3.1.3. Forwarding plane at Failure (when pPE is unreachable)15 3.2. Hybrid IP core...........................................16 3.2.1. Control Plane.......................................16 3.2.2. Forwarding Plane during Steady State (when pPE is reachable).................................................17 3.2.3. Forwarding plane at Failure (when pPE is unreachable)17 4. Rules for Choosing and Managing the Repair path...............17 4.1. General Rules for Managing the Repair Path...............18 4.2. Rules for Choosing the Repair Path for Labeled Prefixes..19 5. Inter-operability with Existing IP FRR Mechanisms.............19 6. Example.......................................................20 6.1. Control Plane............................................21 6.2. Forwarding Plane at Steady State (When PE0 is reachable).22 6.3. Forwarding Plane at Failure (When PE0 is not reachable)..24 7. Security Considerations.......................................25 8. IANA Considerations...........................................25 9. Conclusions...................................................25 10. References...................................................26 10.1. Normative References....................................26 10.2. Informative References..................................27 11. Acknowledgments..............................................27 Appendix A. Other Algorithms to Allocate and Disseminate Vector labels...........................................................28 A.1. iPE chooses the repair path..............................28 A.1.1. Allocating Vector Labels using a Hash Function......28 A.1.1.1.1. Calculating and distributing the mapping rNH- >vL to different routers.............................28 A.1.1.1.2. Risk of Mis-configuration leading to Mismatch in rNH-->vL Mapping..................................29 A.1.1.1.3. Risk of forwarding to Incorrect VRF during convergence only.....................................29 A.1.2. pPE Allocates and advertises vL with protected prefixes ...........................................................29 A.1.2.1.1. Risk of forward to Incorrect VRF during Convergence Only.....................................30 A.2. pPE chooses rPE and distributes the mapping of vL-->rNH..30 A.3. Combination of iPE and pPE Choosing rPE.................31 1. Introduction In a BGP free core, where traffic is tunneled between edge routers, BGP speakers advertise reachability information about prefixes to other edge routers but not to core routers. For labeled address families, namely AFI/SAFI 1/4, 2/4, 1/128, and 2/128, an edge router assigns local labels to prefixes and associates the local label with each advertised prefix such as L3VPN [10], 6PE [11], and Bashandy Expires January 7, 2013 [Page 3] Internet-Draft BGP FRR Using Vector Labels July 2012 Softwire [9]. Suppose that a given edge router is chosen as the best next-hop for a prefix P/m. An ingress router that receives a packet from an external router and destined to the prefix P/m "tunnels" the packet across the core to that egress router. If the prefix P/m is a labeled prefix, the ingress router pushes the label advertised by the egress router before tunneling the packet to the egress router. Upon receiving the packet from the core, the egress router takes the appropriate forwarding decision based on the content of the packet or the label pushed on the packet. In modern networks, it is not uncommon to have a prefix reachable via multiple edge routers. One example is the best external path [8]. Another more common and widely deployed scenario is L3VPN [10] with multi-homed VPN sites. As an example, consider the L3VPN topology depicted in Figure 1. PE1 .............+ | +--------+---------------+ | | | VPN 1 Network | | | | VPN prefix | | (10.0.0.0/8) | | | +---+--------------------+ | /------CE1 / / BGP-free core P--------PE0 \ \ \------CE2 | +---+--------------------+ | | | VPN 2 Network | | | | VPN prefix | | (20.0.0.0/8) | | | +--------+---------------+ | PE2 .............+ Figure 1 VPN prefix reachable via multiple PEs Bashandy Expires January 7, 2013 [Page 4] Internet-Draft BGP FRR Using Vector Labels July 2012 As illustrated in Figure 1, the edge router PE0 is the primary NH for both 10.0.0.0/8 and 20.0.0.0/8. At the same time, both 10.0.0.0/8 and 20.0.0.0/8 are reachable through the other edge routers PE1 and PE2, respectively. 1.1. Conventions used in this document 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 RFC-2119 [1]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying RFC-2119 significance. 1.2. Terminology This section defines the terms used in this document. For ease of use, we will use terms similar to those used by L3VPN [10] o BGP-Free core: A network where BGP prefixes are only known to the edge routers and traffic is tunneled between edge routers o External prefix: It is a prefix P/m (of any AFI/SAFI) that a BGP speaker has an external path. The BGP speaker may learn about the prefix from an external peer through BGP, some other protocol, or manual configuration. The protected prefix is advertised to some or all of the internal peers. o Protectable prefix: It is an external prefix P/m of any AFI/SAFI) that a BGP speaker has an external path to and is eligible to have a repair path. o Protected prefix: It is an external prefix P/m (of any AFI/SAFI) that a BGP speaker has an external path to and also has a repair path to. o Primary Egress PE, "ePE": It is an IBGP peer that can reach the prefix P/m through an external path and advertised the prefix to the other IBGP peers. The primary egress PE was chosen as the best path by one or more internal peers. In other words, the primary egress PE is an egress PE that will normally be used by some ingress PEs when there is no failure. Referring to Figure 1, PE0 is an egress PE. Bashandy Expires January 7, 2013 [Page 5] Internet-Draft BGP FRR Using Vector Labels July 2012 o Protected egress PE, "pPE" (Protected PE for simplicity): It is an egress PE for which there exists a repair path for some or all of the prefixes to which it has an external path. Referring to Figure 1, PE0 is a protected egress PE. o Protected edge router: Any protected egress PE. o Protected next-hop (pNH): It is an IPv4 or IPv6 host address belonging to the protected egress PE. Traffic tunneled to this IP address will be protected via the mechanism proposed in this document. Note that, in most cases, the protected next-hop will be different from the next-hop attribute in the BGP update message [2][3]. o CE: It is an external router through which an egress PE can reach a prefix P/m. The routers "CE1" and "CE2" in Figure 1 are examples of such CEs. o Ingress PE, "iPE": It is a BGP speaker that learns about a prefix through another IBGP peer and chooses that IBGP peer as the next-hop for the prefix. o Repairing P router "rP" (Also "Repairing core router" and "repairing router"): A core router that attempts to restore traffic when the primary egress PE is no longer reachable without waiting for IGP or BGP to re-converge. The repairing P router restores the traffic by rerouting the traffic (through a tunnel) towards the pre-calculated repair PE when it detects that the primary egress PE is no longer reachable. Referring to Figure 1, the router "P" is the repairing P router. o Repair egress PE "rPE" (Repair PE for simplicity): It is an egress PE other than the primary egress PE that can reach the protected prefix P/m through an external neighbor. The repair PE is pre-calculated via other PEs prior to any failure. Referring to Figure 1, PE1 is the repair PE for 10.0.0.0/8 while PE2 is the repair PE for 20.0.0.0/8. o Underlying Repair label (rL): The underlying repair label is the label that is advertised by rPE and is used by rPE to forward repaired traffic, which is traffic re-tunneled by the rP after detecting that the pPE is no longer reachable. A repair label is defined for labeled protected prefixes only. o Repair next-hop (rNH): It is an IPv4 or IPv6 host address belonging to the repair egress PE. If the protected prefix is advertised via BGP, then the repair next-hop MAY be the next-hop attribute in the BGP update message [2][3]. Bashandy Expires January 7, 2013 [Page 6] Internet-Draft BGP FRR Using Vector Labels July 2012 o BGP nexthop (bgpNH): This is the usual next-hop attribute for route advertisements as specified in [2]in [3]. In most case, bgpNH is different from pNH o Vector Label (vL): It is a label that identifies the repair PE within a certain label context. Every distinct rPE must have a distinct vector label the aforementioned label context. Vector labels in different label contexts may overlap o Repair path (Also Repair Egress Path): It is the repair next- hop. If an underlying repair label exists, the repair path is the repair next-hop together with the underlying repair label. o Primary tunnel: It is the tunnel from the ingress PE to the primary egress PE o Repair tunnel: It is the tunnel from the repairing P router to the repair egress PE 1.3. Problem definition The problem that we are trying to solve is as follows o Even though multiple prefixes may share the same egress router, they have different repair edge router. In Figure 1 above, both 10.0.0.0/8 and 20.0.0.0/8 share the same primary next hop PE0, the routing protocol(s) must identify that the node protecting repair node for 10.0.0.0/8 is PE1 while the node protecting repair node for 11.0.0.0/8 is PE2 o On loosing connection to the edge router, the core router "P" MUST reroute traffic towards the *correct* repair edge router that can reach prefixes that were reachable via the failed edge router without waiting for IGP or BGP to re-converge and update the routing tables. On the failure of PE0 illustrated in Figure 1, the core router P needs to reroute traffic for 10.0.0.0/8 towards PE1 and traffic for 11.0.0.0/8 towards PE2 o The repairing core router P MUST NOT be forced to learn about the BGP prefixes on any of the edge router. The same applies for all core routers. o There SHOULD NOT be a need for a special router or group of routers to handle rerouting traffic on edge node failure. o The size of the routing table on any core router MUST be independent of the number of BGP prefixes in the network. Bashandy Expires January 7, 2013 [Page 7] Internet-Draft BGP FRR Using Vector Labels July 2012 o Rerouting traffic without waiting for IGP and BGP to re-converge after a failure MUST NOT cause loops. o For labeled prefixes, when a packet gets re-routed to the repair PE, the label stack on the packet MUST ensure correct forwarding. o Provisioning and maintenance overhead must be kept at minimum o At steady state, when pPE is reachable, paths taken by traffic must not be impacted by deploying the solution proposed in this document unless desired by the operator. o The solution must be incrementally deployable 2. Overview of BGP FRR in an MPLS Core The solution proposed in this document relies on the collaboration of egress PE, ingress PE, penultimate hop routers, and repairing core router. This section gives an overview of how to the solution works for both labeled (AFI/SAFI 1/4, 2/4, 1/128, and 2/128) and unlabeled (AFI/SAFI 1/1, 2/1, 1/2, and 2/2) protected prefixes in an MPLS core. Specifications of the solution in IP core are provided in Section 3. 2.1. Control Plane operation 1. Each egress router that is capable of handling repaired traffic assigns each protectable labeled prefix a repair label: "rL". "rL" is advertised as optional path attribute. "rL" MUST be Per-CE or per-VRF for good BGP attribute packing and forwarding simplicity. For unlabeled prefix, no repair label is needed. A router that is capable of handling repaired traffic is called a repair PE "rPE". a. The semantics of the repair label "rL" is: i. If "rL" is per-CE, then pop *two* labels and send the packet to the appropriate CE ii. If "rL" is per-VRF, then pop *two* labels and forward the packet based on the contents under the two popped labels 2. Each protectable egress PE (pPE) is assigned a unique protectable IP address "pNH". Traffic tunneled to pNH is protected by the BGP FRR proposed in this document a. Only a single pNH is needed per pPE Bashandy Expires January 7, 2013 [Page 8] Internet-Draft BGP FRR Using Vector Labels July 2012 b. If all iPE's support the BGP FRR scheme proposed in this document, then pNH may be the usual BGP next-hop attribute. Otherwise, pNH MUST NOT be identical to the BGP next-hop attribute c. pPE advertises pNH as a prefix into IGP d. pPE advertises an explicit label for pNH (instead of the usual implicit NULL). This way if the penultimate hop does not understand the BGP FRR scheme proposed in this document, pPE can handle the special popping behavior for protected traffic tunneled to pNH e. "pPE" advertises the protected next-hop "pNH" to the penultimate hops to indicate that traffic flowing through the tunnel to the tail end "pNH" is protected against the failure of the node "pPE" and requires special processing by the penultimate hop as will be described in the next few steps f. For every BGP next-hop (bgpNH) that pPE advertises with its routes, pPE separately advertises the mapping (bgpNH,pNH) to all ingress PE. A method analogous to how tunnel information is advertised [4] can be used to advertise this mapping to ingress PE's. The mapping "(bgpNH,pNH)" means: if the ingress PE wants to protect traffic normally tunneled to "bgpNH" against the failure of "pPE", the iPE MUST tunnel the traffic to "pNH" instead of bgpNH. 3. If a pPE knows that a P/m to which it has an external path is also reachable via another PE, a. pPE chooses one of the other PEs as a repair PE "rPE". The pPE chooses, as a repair next-hop, an IP address "rNH" local to or advertised by rPE. Rules governing rNH are i. "rNH" SHOULD be the next-hop attribute advertised by rPE when it announces reachability to the protected prefix P/m to minimize the number of prefixes advertised into IGP and BGP. ii. if rPE also advertised a protected next-hop (pNH) for any BGP prefix that rPE can protect, then rNH MUST NOT be any protected next-hop (pNH) advertised by rP b. pPE assigns a vector label "vL" for "rNH". A distinct "vL" is needed for every distinct "rNH" within the context of a pPE Bashandy Expires January 7, 2013 [Page 9] Internet-Draft BGP FRR Using Vector Labels July 2012 c. pPE advertises the mapping (pNH,rNH,vL) to all ingress PE's. The mapping (pNH,rNH,vL) means: "Within the context of the protected next-hop pNH, the repair next-hop rNH is assigned the vector label vL" d. "pPE" advertises the triplet (pNH,rNH,vL) to candidate repairing core routers. For example, an LDP optional TLV can be used for this purpose 4. An ingress PE "iPE" receives route updates from pPE with "bgpNH" as the next-hop attribute. Suppose an ingress PE "iPE" chooses "bgpNH" as the best path for one or more protectable PE. If iPE wants to protect traffic tunneled to "bgpNH" against pPE failure, "iPE" performs the following steps a. iPE receives the mapping (bgpNH,pNH) from pPE to indicate that the protected next-hop for traffic tunneled to bgpNH is pNH b. iPE receives the mapping (pNH,rNH,vL) from "pPE" to indicate that the vector label pointing to the repair next-hop "rNH" for traffic tunneled to pNH is "vL" c. iPE receives an advertisement for the protectable route from rPE with "rNH" as the next-hop d. If the above 3 conditions are satisfied, then iPE chooses rPE as the repair PE with rNH as the repair next-hop and the vector label "vL" As a result of the above steps, the following nodes store the following information o Ingress PE (iPE) o Receives from pPE NLRI advertisement for the protected labeled prefix P/m containing the usual BGP next-hop attribute "bgpNH" o Receives from pPE the mapping (bgpNH,pNH). This means that if iPE wants to protect traffic normally tunneled to "bgpNH" against pPE failure, the iPE MUST tunnel the traffic to "pNH" instead of "bgpNH" Bashandy Expires January 7, 2013 [Page 10] Internet-Draft BGP FRR Using Vector Labels July 2012 o Receives the triplet (pNH,rNH,vL). The triplet (pNH,rNH,vL) means that if iPE chooses rNH as the repair next-hop for the traffic tunneled to the protected next-hop pNH, then iPE has to use the vector label "vL" while tunneling traffic. The method of using the vector label "vL" is described in the forwarding behavior in Section 2.2 and 2.3. o Penultimate Hop o Receives the "pNH" from pPE o As such, it knows the pNH needs certain special treatment as described in the forwarding behavior in Section 2.2 and 2.3. o Penultimate hop advertises "pNH" as its own prefix into IGP. The penultimate hop advertises pNH so that when pPE is lost, nodes continue to forward the traffic towards the original pPE and hence get protected by the rP. This behavior is required until BGP on the iPE's recalculate and start forwarding traffic towards an alternative PE. o Penultimate hop advertises "pNH" as its own prefix into IGP but with one of the following conditions . For link-state IGPs, "pNH" MAY be advertised with *maximum metric* so as not to affect the path taken by the traffic flowing from iPE's to pPE's . For distance vector IGPs, the penultimate hop advertises metric of "pNH" as follows PHP-metric(pNH) = pPE-metric(pNH) + metric-From-PHP-to-pPE That is, the metric advertised by the penultimate hop for pNH equals the metric advertised by pPE for pNH plus the metric from the penultimate hop to pPE . This way the advertisement of pNH by the penultimate hop into IGP does not impact the path taken by the traffic from iPE's to pPE's Bashandy Expires January 7, 2013 [Page 11] Internet-Draft BGP FRR Using Vector Labels July 2012 . When does the penultimate hop stop advertising pNH as its own prefix? The penultimate hop should continue to advertise pNH long enough for iPE's to re-converge. Advertising pNH longer than necessary is harmless because iPE's would have already re-converged to a new BGP next- hop and hence no traffic will be attracted to the non- existing pNH. The specific period length can be subject to configuration but the default value may be in the order of 2-3 minutes o Repairing core router "rP" (which may also be the penultimate hop) o Receives the triplet (pNH,rNH,vL) from pPE o Creates a distinct label context for "pNH" . In LDP core, the context is identified by the IGP label of pNH . In an IP core, the context is identified by the "pNH" address itself. o Inserts the label vL in the label context identified by pNH. . The forwarding entry for vL in the label context of pNH is . Swap vL with the IGP label of rNH . Forward the packet towards rNH o Installs the following forwarding entry for pNH . If pNH is not reachable, pop the label for pNH and lookup the label underneath the label of pNH in the label context of pNH . Otherwise, forward the packet to pNH as usual What is left it to outline the forwarding behavior before and after the failure of "pNH". 2.2. Forwarding behavior at Steady State (while pPE is reachable) This section outlines the packet forwarding procedure when pPE is still reachable. 1. Ingress PE (iPE) receives a packet matching P/m from an external neighbor and reachable via pPE Bashandy Expires January 7, 2013 [Page 12] Internet-Draft BGP FRR Using Vector Labels July 2012 2. Ingress PE: Pushes *four* labels o Bottom label: VPN label advertised by pPE o Second label: rL o Third label: vL corresponding to chosen rNH o Top label: IGP label towards pNH (not the bgpNH attribute) o In pushing the labels "vL" following by "rL", iPE practically encodes the chosen repair path into the packet. 3. Penultimate Hop a. Receives a packet with top label bound to pNH b. Pops *three* labels *all the time*. c. Sends packet to pNH 4. Protected Egress PE (pPE) a. Receives a packet with top label as VPN label b. Forwards the packet as usual Thus the packet can be delivered correctly to its destination. 2.3. Forwarding behavior when pPE Fails The repairing router "rP" directly connected to a failure detects that pNH is no longer reachable. The following steps are applied. 1. Repairing router "rP" a. Receives packet with top label bound to pNH b. pNH is not reachable c. Pop the label of pNH. The vector label "vL" is right under the label of pNH d. Lookup "vL" in the label context identified by the label of "pNH". The lookup yields a rewrite label corresponding to the chosen rNH e. Swap the top label with the label of rNH Bashandy Expires January 7, 2013 [Page 13] Internet-Draft BGP FRR Using Vector Labels July 2012 f. Send packet towards rNH g. In effect, the repairing router uses the vector label to find the repair PE chosen by the ingress PE 2. Penultimate hop of rPE a. rNH is not a protected NH for rPE b. Thus the penultimate hop employs the usual penultimate (single label) hop popping and then forwards the packet to rPE 3. Repair PE (rPE) a. Receives packet with top label rL (which rPE advertised) and the bottom label is the regular VPN label advertised by the primary PE "pPE" b. Make a lookup on "rL" c. rL per CE i. Pop *two* labels. ii. Send to correct CE d. rL per VRF i. Pop *two* labels. ii. Make IP lookup in appropriate VRF iii. Send to the CE To protect unlabeled traffic there is no need for dual label popping or "rL". Instead, all the repairing router needs to do when it detects that "pNH" is no longer reachable is to re-tunnel the packet towards "rNH" in a regular LSP The next section presents the solution in an IP core. 3. Overview of the BGP FRR using Vector Labels in an IP Core This section describes the BGP FRR using vector labels solution in an IP core for both labeled (AFI/SAFI 1/4, 2/4, 1/128, and 2/128) and unlabeled (AFI/SAFI 1/1, 2/1, 1/2, and 2/2) protected prefixes. Bashandy Expires January 7, 2013 [Page 14] Internet-Draft BGP FRR Using Vector Labels July 2012 The primary difference between a MPLS core and an IP core is that the tunnels between edge routers are IP based such as [5][6][7]. In this section, we propose two alternatives: A completely pure IP core and a hybrid IP/MPLS core 3.1. Pure IP Core In this section, we propose a scheme by which core routers are incapable of handling any kind of MPLS labels. 3.1.1. Control Plane The pPE still needs to advertise the mapping (bgpNH,pNH) as in Section 2 but it does not allocate or advertise a vector label. The rPE advertises rL with protected prefixes to all its iBGP peer as in MPLS core solution in Section 2. Assume iPE decides that rPE is the repair PE for a protected prefix. o iPE pushes the usual VPN label for labeled prefixes o iPE pushes the repair label "rL" advertised by the chosen rPE o iPE pushes *two* IP tunnel headers on the packet o Repair tunnel header. This will be the inner tunnel header with destination address rNH towards the rPE o Protected tunnel header: This will be the outer tunnel header with destination address pNH towards the pPE 3.1.2. Forwarding plane during Steady State (when pPE is reachable) 1. iPE pushes the VPN label and the repair label followed by the two tunnel headers described in the previous section 2. rP: No special behavior necessary 3. pPE a. Decapsulates *two* tunnel headers and the repair label "rL" b. Uses the contents of the packet underneath 3.1.3. Forwarding plane at Failure (when pPE is unreachable) 1. iPE is not yet aware of the failure so its behavior remains the unchanged. Bashandy Expires January 7, 2013 [Page 15] Internet-Draft BGP FRR Using Vector Labels July 2012 2. rP a. Decapsulates the outer tunnel header towards pNH b. Uses the repair tunnel header to forward the packet towards rPE 3. rPE a. Decapsulates the tunnel header b. Uses the repair label "rL" to forward the packet to the correct CE i. Pop rL and the VPN label under it ii. Use the forward the packet to the correct CE 3.2. Hybrid IP core In this section, we assume that rP is capable of handling MPLS labels 3.2.1. Control Plane The pPE needs to advertise the mapping (bgpNH,pNH). iPE also needs to allocate a vector label for each known rPE and advertise the mapping (pNH,rNH,vL) to all its iBGP peers and to candidate repair core routers. This behavior is identical to iPE behavior in MPLS core in Section 2. The rPE advertises rL with protected prefixes to all its iBGP peer as in the case of MPLS core described in Section 2. Assume iPE decides that rPE is the repair PE for a given prefix: o iPE pushes the usual VPN label for labeled prefix o iPE pushes the repair label "rL" advertised by the chosen rPE o Pushes the vector label of the chosen rPE o iPE pushes two the protected tunnel header: This will be the outer IP tunnel header with destination address pNH towards the pPE rP behavior is identical to its behavior in an MPLS core in Section 2. Bashandy Expires January 7, 2013 [Page 16] Internet-Draft BGP FRR Using Vector Labels July 2012 3.2.2. Forwarding Plane during Steady State (when pPE is reachable) 4. iPE pushes the two tunnel headers described in the previous section 5. rP: No special behavior necessary 6. pPE a. Decapsulates the outer tunnel headers plus *two* labels (vL and rL b. Uses the contents of the packet after decapsulation to forward the packet 3.2.3. Forwarding plane at Failure (when pPE is unreachable) 7. iPE is not yet aware of the failure so its behavior remains the same 8. rP a. Decapsulates the tunnel header towards pNH b. Pops the vector label "vL" c. Looks up the vector label "vL" in the label context identified by pNH. The lookup should yield the rNH d. Encapsulates the packet into a tunnel header with destination address rNH and forwards the packet towards rPE 9. rPE a. Decapsulates the tunnel header b. Uses the repair label "rL" to forward the packet to the correct CE i. Pop *two* labels for labeled traffic ii. Forward the packet to the correct CE 4. Rules for Choosing and Managing the Repair path This section specifies rules governing how a protectable edge router pPE chooses and advertises the repair path. Other than the rules in this section, the method of choosing the repair path is beyond the scope of this document. Bashandy Expires January 7, 2013 [Page 17] Internet-Draft BGP FRR Using Vector Labels July 2012 4.1. General Rules for Managing the Repair Path This section specifies general rules for choosing the repair path for both labeled and unlabeled prefixes. 1. A repair PE MUST be another edge router that advertises the same prefix to the protected edge router pPE via IBGP peering. 2. If a repairing P router "rP" determines that the path taken by the repair tunnel to a repair edge router rPE passes through the protected edge router pPE, then the repairing router "P" MUST NOT install this repair path in its forwarding plane. Instead, the repairing "p" router MAY use other paths that do not pass through pPE or use existing core FRR mechanisms such as [12], [13], and [14]. 3. Let the protected next-hop pNH match the IGP route pR. If the "rP" determines that the repair tunnel to a repair edge router passes through a next-hop of the IGP route pR, then the repairing router SHOULD NOT install this repair path in its forwarding plane. 4. A protected next-hop uniquely identifies an protected PE within a BGP-free core. Thus a protected next-hop NH MUST NOT be advertised by two different pPEs. 5. At any point in time, for the same primary and repair next-hops pNH and rNH, only one advertisement is valid. Thus for the same value of pNH and rNH, an advertisement of the pair (pNH,rNH) MUST override or be preceded by the withdrawal of any previously advertised pair (pNH,rNH). 6. If the repair PE "rPE" advertises one or more protected next- hops, then the repair next-hop "rNH" MUST be different from any protected next-hop "pNH" advertised by rPE If rules (1), (2), and(3), then the tunnel to the repair edge router rPE does not provide protection against the failure of the edge node ePE. Instead it provides core protection against the failure of the path through the core leading to the protected edge node pPE. Thus existing core FRR protection mechanisms such as those specified in [12], [13], and [14] can be used instead. Rules (4), (5), and (5) ensures that there is no ambiguity about the primary and repair next-hops Bashandy Expires January 7, 2013 [Page 18] Internet-Draft BGP FRR Using Vector Labels July 2012 4.2. Rules for Choosing the Repair Path for Labeled Prefixes This section specifies rules in additions to those mentioned in Section 4.1 by which an edge router iPE chooses and advertises the repair path for a protected labeled prefix P/m. A edge router iPE MUST only choose the edge router rPE and the underlying repair label rL as a repair path for the prefix P/m if the "rL" allocated on per-VPN or per-CE/per-next-hop basis. The reason for this rule is that "rL" is advertised as path attributes in MP/BGP updates. If "rL" is allocated on per-prefix basis, then attribute packing will be severely impacted 5. Inter-operability with Existing IP FRR Mechanisms Current existing IP FRR mechanisms can be divided into two categories: core protection and edge protection. Core protection techniques, such as [12], [13], and [14], provide protection against internal node and/or link failure. Thus the technique proposed in this document is not related to existing IP FRR mechanisms. If the failure of an internal node or link results in completely disconnecting a protectable edge node, then an administrator MAY configure the repairing router to prefer the technique proposed in this document over existing IP FRR mechanisms. Edge protection techniques, such as [16] provide protection against the failure of the link between PE and CE routers. Thus existing PE- CE link protection can co-exist with the techniques proposed in this document because the two techniques are independent of each other. Bashandy Expires January 7, 2013 [Page 19] Internet-Draft BGP FRR Using Vector Labels July 2012 6. Example We will use and LDP core as an example. Consider the diagram depicted in Figure 2 below. We assume that the PEs advertise repair labels as specified in [15] +-----------------------------------+ | | | LDP Core | | | | PE1 Lo = 9.9.9.1 | |\ | | \ | | \ | | \ | | CE1.......VRF "Blue" | | / (10.0.0.0/8) | | / (11.0.0.0/8) | | / | |/ PE11 P--------PE0 Lo1 = 1.1.1.1/32 | |\ Lo2 = 1.1.1.2/32 | | \ | | \ | | \ | | CE2.......VRF "Red" | | / (20.0.0.0/8) | | / (21.0.0.0/8) | | / | |/ | PE2 Lo = 9.9.9.2 | | | | +-----------------------------------+ Figure 2 : Edge node BGP FRR in LDP core o In Figure 2, PE0 is the pPE for VRFs "Blue" and "Red". PE1 and PE2 are the rPEs for VRFs "Blue" and "Red", respectively. VRF Blue has 10.0.0.0/8 and 11.0.0.0/8 and VRF Red has 20.0.0.0/8 and 21.0.0.0/8 o Assuming PE0 uses per prefix label allocation, PE0 assigns the VPN labels 4100, 4200, 4300, and 4400 to 10.0.0.0/8, 11.0.0.0/8, 20.0.0.0/8, and 21.0.0.0/8 respectively. PE0 advertises the prefixes 10.0.0.0/8, 11.0.0.0/8, 20.0.0.0/8, and 21.0.0.0/8 using MP/BGP as usual Bashandy Expires January 7, 2013 [Page 20] Internet-Draft BGP FRR Using Vector Labels July 2012 6.1. Control Plane 1. rPEs Allocate and advertise Repair labels a. Acting as a rPE, PE1 allocates (on per-CE basis) and advertises a repair label rL1=3100 with the prefixes 10.0.0.0/8 and 11.0.0.0/8 to all iBGP peers b. Similarly, PE2 allocates and advertises the repair label rL2=3200 with the prefixes 20.0.0.0/8 and 21.0.0.0/8 2. pPE calculates and advertises the pNH a. Assume that PE0 uses "Loopback0" as the BGP next-hop, PE0 automatically picks Loopback2 as the pNH. As such PE0 advertises (bgpNH,pNH)=(1.1.1.1,1.1.1.2) to all iBGP peers including the iPE PE11. b. When the iPE "PE11" receives (bgpNH,pNH)=(1.1.1.1,1.1.1.2), PE11 understands that if it wants to protect traffic whose bgpNH=1.1.1.1 against the failure of the node 1.1.1.1, PE11 has to tunnel the traffic to 1.1.1.2 instead of 1.1.1.1 3. pPE allocates and advertizes vector labels a. On receiving the repair labels 3100 and 3200 from PE1 and PE2, respectively, PE0 detects that there are two rPEs: PE1 and PE2. AS such PE0 assigns two vector labels vL1 = 1100 and vL2 = 1200 to PE1 and PE2, respectively b. PE0 advertises (1.1.1.2, 9.9.9.1, 1100) and (1.1.1.2, 9.9.9.2, 1200) to all iBGP peers, including the ingress PE PE11 c. On receiving (1.1.1.2, 9.9.9.1, 1100) and (1.1.1.2, 9.9.9.2, 1200), the ingress PE PE11 understand that if it were to pick 9.9.9.1 as the rPE for packet tunneled to 1.1.1.2, then it has to push the vector lagbel 1100. Similarly, to protect a packet tunneled to 1.1.1.2 using the rPE 9.9.9.2, then it has to push the vector label 1200. d. PE0 also advertises (1.1.1.2, 9.9.9.1, 1100) and (1.1.1.2, 9.9.9.2, 1200) to all candidate repairing core routes, including the core router "P". 4. The repairing core router creates the repair state Bashandy Expires January 7, 2013 [Page 21] Internet-Draft BGP FRR Using Vector Labels July 2012 a. Acting as a rP, the core router "P" receives the advertisements (1.1.1.2, 9.9.9.1, 1100)and (1.1.1.2, 9.9.9.2, 1200) from PE0. b. rP understands that it has to pop *3* labels when it receives a packet whose top label is the LDP label for 1.1.1.2 c. rP creates a label context identified by the LDP label of 1.1.1.2/32 d. rP inserts the following two label entries in the created label context i. 1100-->9.9.9.1 ii. 1200-->9.9.9.2 5. The ingress PE calculates the rPEs a. PE11 receives an advertisement for 10.0.0.0/8, 11.0.0.0/8, 20.0.0.0/8, and 21.0.0.0/8 from PE0 with the BGP next- hop=1.1.1.1. Because PE11 received (bgpNH,pNH)=(1.1.1.1,1.1.1.2) from PE0, then PE11 knows that to protect traffic tunneled to PE0, it has to tunnel the traffic to 1.1.1.2 instead of 1.1.1.1 b. PE11 receives an advertisement from PE1 for 10.0.0.0/8 and 11.0.0.0/8 with the repair label 3100 c. Hence PE11 picks PE1 as the rPE for the prefixes 10.0.0.0/8 and 11.0.0.0/8 with rNH=9.9.9.1 and rL=3100. Remember that the vector label for 9.9.9.1 is 1100. d. Similarly, PE11 receives an advertisement from PE2 for 20.0.0.0/8 and 21.0.0.0/8 with the repair label 3200 e. Hence PE11 picks PE2 as the rPE for the prefixes 10.0.0.0/8 and 11.0.0.0/8 with rNH=9.9.9.2 and rL=1200. Remember that the vector label for 9.9.9.1 is 1100. 6.2. Forwarding Plane at Steady State (When PE0 is reachable) 1. Ingress PE PE11 a. Traffic for VRF "Blue" i. PE11 receives a packet for VRF Blue with destination address 10.1.1.1 from an external router. Bashandy Expires January 7, 2013 [Page 22] Internet-Draft BGP FRR Using Vector Labels July 2012 ii. PE11 pushes the following labels 1. The VPN label 4100 2. The Repair label 3100 3. The vector label 1100 4. The LDP label for 1.1.1.2 b. Traffic for VRF "Red" i. PE11 receives a packet for VRF Red with destination address 20.1.1.1 from an external router ii. PE11 pushes the following labels 1. The VPN label 4300 2. The Repair label 3200 3. The vector label 1200 4. The LDP label for 1.1.1.2 2. Penultimate Hop of PE0 (Which is also the rP "P") a. Receives a packet with top label for the protected next-hop 1.1.1.2 b. Pops *3* labels c. Forwards the packet to 1.1.1.2 3. Protected PE PE0 a. Traffic for VRF "Blue" i. PE0 receives traffic with the top label 4100. ii. 4100 is the VPN label for VRF "Blue" iii. PE0 pops the label 4100 and forwards the packet to CE1 b. Traffic for VRF "Red" i. PE0 receives traffic with the top label 4300. ii. 4300 is the VPN label for VRF "Red" Bashandy Expires January 7, 2013 [Page 23] Internet-Draft BGP FRR Using Vector Labels July 2012 iii. PE0 pops the label 4300 and forwards the packet to CE2 6.3. Forwarding Plane at Failure (When PE0 is not reachable) 1. The ingress PE PE11 Does not know about the failure yet and hence it does not change its behavior. 2. Repair PE rP a. Traffic for VRF "Blue" i. Receives a packet with the top label being the LDP label for 1.1.1.2 ii. 1.1.1.2 is not reachable iii. Pop the LDP label of 1.1.1.2. The vector label 1100 is under it iv. Lookup the vector 1100 in the label context of 1.1.1.2. The lookup yields the LDP label of the rNH 9.9.9.1 v. Swap the vector label 1100 with the LDP label of the of 9.9.9.1 and forward the packet towards PE1 b. Traffic for VRF "Red" i. Receives a packet with the top label being the LDP label for 1.1.1.2 ii. 1.1.1.2 is not reachable iii. Pop the LDP label of 1.1.1.2. The vector label 1200 is under it iv. Lookup the vector 1200 in the label context of 1.1.1.2. The lookup yields the LDP label of the rNH 9.9.9.2 v. Swap the vector label 1200 with the LDP label of the of 9.9.9.2 and forward the packet towards PE2 3. The repair Router "PE1" a. The penultimate hop of PE1 performs the usual penultimate hop popping Bashandy Expires January 7, 2013 [Page 24] Internet-Draft BGP FRR Using Vector Labels July 2012 b. PE1 receives a packet with the top label equals the repair label 3100, which was allocated on per-CE basis and points to CE1 c. PE1 pops *2* labels and forwards the packet to CE1 4. The repair Router "PE2" a. The penultimate hop of PE2 performs the usual penultimate hop popping b. PE1 receives a packet with the top label equals the repair label 3200, which was allocated on per-CE basis and points to CE2 c. PE2 pops *2* labels and forwards the packet to CE2 7. Security Considerations No additional security risk is introduced by using the mechanisms proposed in this document 8. IANA Considerations No requirements for IANA 9. Conclusions This document proposes a method that allows fast re-route protection against edge node failure or complete disconnected from the core in a BGP-free core. The method proposed has the following advantages o Very scalable: o No router has to copy the routing table of another router o Minimum additional prefixes injected in the core. In fact, at most one additional prefix per pPE is injected and only if there is no spare IP address on the pPE o Minimal provisioning overhead: o If there is a spare IP address on the pPE, then the provisioning effort is just enablement. If not, then the provisioning effort is just to configure a distinct IP address on each pPE to act as the pNH. Bashandy Expires January 7, 2013 [Page 25] Internet-Draft BGP FRR Using Vector Labels July 2012 o Absolutely no restriction on which PE is connected to which VRF. o On a PE where BGP FRR is already configured, moving, connecting, or disconnecting a CE to/from the PE requires zero operator intervention to protect prefixes. o Immunity to misconfigation: the only configuration that may be required is a distinct pNH on each pPE. The mapping (bgpnh,pPE) and (pNH,rNH,vL) is advertised to all BGP peers. If the operator configures the same pNH on two different pPE, then the misconfiguration will be detected almost immediately o No Need for IP or TE FRR: Because the exit point of the repair tunnel from rP to rPE is different from the primary tunnel exit point o Works in both MPLS core and IP core o Works with per-CE, per-VRF and per-prefix label allocation o Can be incrementally deployed. There is no flag day. Different routers can be upgraded at different times o Zero impact on the paths taken by traffic: Enabling/deploying the feature described in this document has no effect on the paths taken by traffic at steady state 10. References 10.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4), RFC 4271, January 2006 [3] Bates, T., Chandra, R., Katz, D., and Rekhter Y., "Multiprotocol Extensions for BGP", RFC 4760, January 2007 [4] Malhotra, P. and Rosen, E., " The BGP Encapsulation Subsequent Address Family Identifier (SAFI) and the BGP Tunnel Encapsulation Attribute", RFC 5512, April 2009 [5] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed., "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005. Bashandy Expires January 7, 2013 [Page 26] Internet-Draft BGP FRR Using Vector Labels July 2012 [6] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [7] Perkins, C., "IP Encapsulation within IP", RFC 2003, October 1996. 10.2. Informative References [8] Marques,P., Fernando, R., Chen, E, Mohapatra, P., Gredler, H., "Advertisement of the best external route in BGP", draft-ietf- idr-best-external-04.txt, April 2011. [9] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh Framework", RFC 5565, June 2009. [10] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, February 2006. [11] De Clercq, J. , Ooms, D., Prevost, S., Le Faucheur, F., "Connecting IPv6 Islands over IPv4 MPLS Using IPv6 Provider Edge Routers (6PE)", RFC 4798, February 2007 [12] Atlas, A. and A. Zinin, "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, September 2008. [13] Shand, S., and Bryant, S., "IP Fast Reroute", RFC5714, January 2010 [14] Shand, M. and S. Bryant, "A Framework for Loop-Free Convergence", RFC 5715, January 2010. [15] Bashandy, A., Pithawala, P., and Heitz, J., "Scalable, Loop- Free BGP FRR using Repair Label", draft-bashandy-idr-bgp- repair-label-02.txt", July 2011 [16] O. Bonaventure, C. Filsfils, and P. Francois. "Achieving sub-50 milliseconds recovery upon bgp peering link failures," IEEE/ACM Transactions on Networking, 15(5):1123-1135, 2007 11. Acknowledgments Special thanks to Clarence Filsfils, Eric Rosen, Stewart Bryant, and Pradosh Malhotra for the valuable comments This document was prepared using 2-Word-v2.0.template.dot. Bashandy Expires January 7, 2013 [Page 27] Internet-Draft BGP FRR Using Vector Labels July 2012 Appendix A. Other Algorithms to Allocate and Disseminate Vector labels This section outlines two alternate algorithms for Allocating and distributing vector label "vL" to "rPE" mapping. The alternate algorithms can be divided into two categories, iPE chooses the repair path and pPE chooses the repair path A.1. iPE chooses the repair path A.1.1. Allocating Vector Labels using a Hash Function In the method of allocating and advertising vector labels outlined in Sections 2 and 3 each pPE allocates and binds a vector label to each known rPE. As a result, the same rPE may be bound to multiple vector labels by multiple pPEs and thus requiring additional storage on the rP. In this section, we propose a method by which a vector label is computed using a hash function based on the numerical value of rNH A.1.1.1.1. Calculating and distributing the mapping rNH->vL to different routers 1. We assume that all routers in a BGP free core, including edge router, agree on the set of candidate repair next-hops. This can be achieved via default behavior (e.g. all host routes) or some sort of configuration, such as ISIS administrative tags 2. No need for pPE to advertise the (pNH,rNH,vL) to iPE or rP 3. Each candidate rP and iPE calculates the vL for each candidate repair next-hop rNH 4. The rP inserts the calculated mapping vL-->rNH in a "repair label context" that is common for all protected PEs instead of having separate label context for each pPE. 5. If iPE chooses rNH as the repair next-hop for traffic tunneled to pNH, iPE calculates the vL corresponding to the chosen rNH and pushes vL as described in Sections 2.1. 6. On pPE failure, the lookup for vL occurs in the common "repair label context" IN the next subsections, we outline two risks of using the hash function for rNH-->vL mapping. Bashandy Expires January 7, 2013 [Page 28] Internet-Draft BGP FRR Using Vector Labels July 2012 A.1.1.1.2. Risk of Mis-configuration leading to Mismatch in rNH-->vL Mapping 1. Due to misconfiguration, some routers may not have the identical sets of candidate repair next-hops "rNH's" or use the same hash function to calculate vL. For example, an upgraded router may have a new hash function enabled or the ISIS administrative tags may not be associated with all candidate rNHs 2. To alleviate this risk, we propose that each rPE associates the calculated value of vL for each rNH in an optional TLV in IGP 3. If a router finds that its calculated value for rNH-->vL is different from the value received from the corresponding rPE, then the router can raise an alarm, A.1.1.1.3. Risk of forwarding to Incorrect VRF during convergence only Identical mapping of rNH-->vL is only guaranteed if the set of candidate rNH is the same on all routers. Because each router calculates rNH-->vL independently, there is a minor risk of forwarding to incorrect VRF. Consider the following example 1. The risk exists even if every rPE advertises the vL of its own rNH 2. Two rNH's, say rNH1 and rNH2, map to the same vL, even if rNH1, and rNH2 protect different prefixes 3. rPE1 and rPE2 have not yet heard each other mappings 4. iPE learns about vL-->rNH1 before vL-->rNH2 5. rP/PLR learns about vL-->rNH2 before vL-->rNH1 6. If pPE fails during the short period before iPE and rP can detect the vL collision, rP re-routes traffic to rNH2 but the repair label pushed by iPE is for rNH1. A.1.2. pPE Allocates and advertises vL with protected prefixes 1. pPE allocates a single vL for all prefixes reachable via the same CE. If two prefixes bound to the same vL are protected by different rPE's, then pPE MUST re-advertise the second protectable prefix with a different vL to all ingress PEs 2. pPE always advertises (pNH, vL) with protected prefixes as optional attributes all the time even if there is no rPE Bashandy Expires January 7, 2013 [Page 29] Internet-Draft BGP FRR Using Vector Labels July 2012 3. iPEs and the pPE agree on the way to pick the rPE. E.g. if there are multiple rPEs, choose the one with lowest router ID 4. When rPE advertises rL for a protected prefix a. Both pPE and iPE will get the update b. Both pPE and iPE will choose the same rPE for the protected prefix 5. iPE associate the correct triplet (pNH, vL, rL) with protected prefixes without getting a re-advertisement for the prefix from pPE 6. pPE Informs about (pNH, rNH, vL) 7. Hence rP/PLR knows that the vector label vL maps to rNH in the label context of pNH. 8. rP/PLR inserts vL-->rNH in the context of pNH A.1.2.1.1. Risk of forward to Incorrect VRF during Convergence Only The conditions for the risk to exist o More than one rNH, say rNH1 and rNH2, protect the same prefix o iPE learns about rNH1 and has not yet learnt about rNH2 o pPE learns about rNH2 and has not yet learnt about rNH1 o pPE fails during this time period How incorrect forwarding can occur o pPE maps vL to rPE2 on rP/PLR while iPE maps vL to rPE1 o pPE fails during this short period, o rP/PLR re-routes the packet to rPE2 but the repair label pushed by iPE belongs to rPE1 (say rL1) A.2. pPE chooses rPE and distributes the mapping of vL-->rNH In Sections 2, 3, and A.1 the ingress PE chooses the rPE for every protectable prefix. While it causes less churn because there is never a need to re-advertise protected prefixes, it is difficult to Bashandy Expires January 7, 2013 [Page 30] Internet-Draft BGP FRR Using Vector Labels July 2012 configure a policy to control the choice of the rPE if the policy has to be applied to all iPEs. In this Section, we propose an algorithm to select rPE and advertise vL-->rNH via pPE instead of iPE 1. pPE allocates a single vL for all prefixes reachable via the same CE a. We assume that prefixes reachable via the same CE or belong to the same VRF are protectable by the same rPE b. If two prefixes bound to the same vL are protected by different rPE's, then pPE MUST re-advertise the second protectable prefix with a different vL to all ingress PEs 2. pPE always advertises (pNH, vL) with protected prefixes as optional attributes all the time even if there is no rPE. Remember that pNH,vL) means the vector label for protected traffic tunneled to pNH is vL 3. Based on rPE advertisement, pPE decides that the repair next-hop for a given protected prefix P/m is rNH. pPE sends the mapping (vL,rNH) similar to [4] as a separate advertisement to iPEs 4. Suppose two prefixes prefixes P1/m1 and P2/m2 are associated with the same vector label vL1 but are protected by two different repair PEs: rNH1 and rNH2 a. Re-advertise P2/m2 with a new vector label vL2 b. pPE sends the mapping( vL1,rNH1) and (vL2,rNH) in a separate advertisement to iPEs c. The re-advertisement of the prefix p2/m2 with the new vector label vL2 must be done BEFORE sending the vector label mapping to guarantee correct forwarding Unlike the schemes in Sections A.1.1 and A.1.2 there is no risk of forwarding to incorrect VRF because pPE is the only source of mapping vL-->rNH A.3. Combination of iPE and pPE Choosing rPE o pPE can choose the rPE by specifying the mapping of vL to rNH, re- advertising/advertising the protected prefix with rNH, or a combination of both o pPE decides the prefixes for which it chooses the rPE based on various factors. For example Bashandy Expires January 7, 2013 [Page 31] Internet-Draft BGP FRR Using Vector Labels July 2012 o Option 1: The operator can configure the prefixes for which the pPE can choose the rPE. o Option 2: If there is more than one rPE, then pPE chooses the rPE. Otherwise, it is left to iPE o There are probably other options o As long as the pPE does not specify the rPE for a prefix, then the iPE is free to choose the rPE, otherwise, the iPE has to abide by pPE choice A combination of iPE and pPE choosing the rPE reduces the provisioning overhead when configuring a policy to choose the rPE at the expense of increasing the churn. Authors' Addresses Ahmed Bashandy Cisco Systems 170 West Tasman Dr, San Jose, CA 95134 Email: bashandy@cisco.com Nagendra Kumar Cisco Systems 170 West Tasman Dr, San Jose, CA 95134 Email: naikumar@cisco.com Maciek Konstantynowicz Cisco Systems 170 West Tasman Dr, San Jose, CA 95134 Email: mkonstan@cisco.com Bashandy Expires January 7, 2013 [Page 32]