Network Working Group B. Kothari Internet-Draft K. Kompella Updates: 4761 (if approved) Juniper Networks Intended status: Standards Track W. Henderickx Expires: January 7, 2010 F. Balus Alcatel-Lucent July 6, 2009 BGP based Multi-homing in Virtual Private LAN Service draft-kothari-henderickx-l2vpn-vpls-multihoming-00.txt Status of this Memo This Internet-Draft is submitted to IETF 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. 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. 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The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 7, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the Kothari, et al. Expires January 7, 2010 [Page 1] Internet-Draft VPLS Multi-homing July 2009 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Kothari, et al. Expires January 7, 2010 [Page 2] Internet-Draft VPLS Multi-homing July 2009 Abstract Virtual Private LAN Service (VPLS) is a Layer 2 Virtual Private Network (VPN) that gives its customers the appearance that their sites are connected via a Local Area Network (LAN). It is often required for the Service Provider (SP) to give the customer redundant connectivity to some sites, often called "multi-homing". This memo shows how multi-homing can be offered in the context of BGP-based VPLS. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. General Terminology . . . . . . . . . . . . . . . . . . . 4 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. VPLS Multi-homing Considerations . . . . . . . . . . . . . 6 3. Multi-homing Operation . . . . . . . . . . . . . . . . . . . . 7 3.1. Provisioning Model . . . . . . . . . . . . . . . . . . . . 7 3.2. Multi-homing NLRI . . . . . . . . . . . . . . . . . . . . 7 3.3. VPLS Preference . . . . . . . . . . . . . . . . . . . . . 8 3.4. Designated Forwarder Election . . . . . . . . . . . . . . 8 3.4.1. BGP Advertisement for VPLS Multi-homing . . . . . . . 9 3.4.2. Tie-breaking Rules . . . . . . . . . . . . . . . . . . 12 3.4.3. DF Election on PEs . . . . . . . . . . . . . . . . . . 12 4. Use of Route Origin Extended Community . . . . . . . . . . . . 14 5. BGP based VPLS . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1. BGP Local Preference . . . . . . . . . . . . . . . . . . . 15 5.2. Multi-AS VPLS . . . . . . . . . . . . . . . . . . . . . . 15 5.2.1. Inter-AS Method (b): EBGP Redistribution of VPLS Information between ASBRs . . . . . . . . . . . . . . 16 5.2.2. Method (c): Multi-Hop EBGP Redistribution of VPLS Information between ASes . . . . . . . . . . . . . . . 17 6. MAC Flush Operations . . . . . . . . . . . . . . . . . . . . . 18 6.1. MAC List FLush . . . . . . . . . . . . . . . . . . . . . . 18 6.2. Implicit MAC Flush . . . . . . . . . . . . . . . . . . . . 18 7. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 20 7.1. BGP based VPLS . . . . . . . . . . . . . . . . . . . . . . 20 7.2. BGP Auto-discovery with LDP for signaling . . . . . . . . 20 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 11.1. Normative References . . . . . . . . . . . . . . . . . . . 24 11.2. Informative References . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 Kothari, et al. Expires January 7, 2010 [Page 3] Internet-Draft VPLS Multi-homing July 2009 1. Introduction Virtual Private LAN Service (VPLS) is a Layer 2 Virtual Private Network (VPN) that gives its customers the appearance that their sites are connected via a Local Area Network (LAN). It is often required for a Service Provider (SP) to give the customer redundant connectivity to one or more sites, often called "multi-homing". [RFC4761] explains how VPLS can be offered using BGP for auto- discovery and signaling; section 3.5 of that document describes how multi-homing can be achieved in this context. [I-D.ietf-l2vpn-signaling] explains how VPLS can be offered using BGP for auto-discovery and [RFC4762] explains how VPLS can be offered using LDP for signaling. This document provides a VPLS multi-homing solution when BGP is used for auto-discovery as described in either [RFC4761] or [I-D.ietf-l2vpn-signaling]. Section 2 lays out some of the scenarios for multi-homing, other ways that this can be achieved, and some of the expectations of BGP-based multi-homing. Section 3 defines the components of BGP-based multi- homing, and the procedures required to achieve this. Section 8 may someday discuss security considerations. 1.1. General Terminology Some general terminology is defined here; most is from [RFC4761] or [RFC4364]. Terminology specific to this memo is introduced as needed in later sections. A "Customer Edge" (CE) device, typically located on customer premises, connects to a "Provider Edge" (PE) device, which is owned and operated by the SP. A "Provider" (P) device is also owned and operated by the SP, but has no direct customer connections. A "VPLS Edge" (VE) device is a PE that offers VPLS services. A VPLS domain represents a bridging domain per customer. A Route Target community as described in [RFC4360] is typically used to identify all the PE routers participating in a particular VPLS domain. A VPLS site is a grouping of ports on a PE that belong to the same VPLS domain. A site is uniquely identified by a site ID, also called as VE ID. Sites are referred to as local or remote depending on whether they are configured on the PE router in context or on one of the remote PE routers (network peers). 1.2. Conventions 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]. Kothari, et al. Expires January 7, 2010 [Page 4] Internet-Draft VPLS Multi-homing July 2009 2. Background This section describes various scenarios where multi-homing may be required, and the implications thereof. It also describes some of the singular properties of VPLS multi-homing, and what that means from both an operational point of view and an implementation point of view. There are other approaches for providing multi-homing such as Spanning Tree Protocol, and this document specifies use of BGP for multi-homing. Comprehensive comparison among the approaches is outside the scope of this document. 2.1. Scenarios The most basic scenario is shown in Figure 1. CE1 is a VPLS CE that is dual-homed to both PE1 and PE2 for redundant connectivity. ............... . . ___ CE2 ___ PE1 . / / : PE3 __/ : Service : CE1 __ : Provider PE4 \ : : \___ CE3 \___ PE2 . . . ............... Figure 1: Scenario 1 CE1 is a VPLS CE that is dual-homed to both PE1 and PE2 for redundant connectivity. However, CE4, which is also in the same VPLS domain, is single-homed to just PE1. CE4 ------- ............... \ . . ___ CE2 ___ PE1 . / / : PE3 __/ : Service : CE1 __ : Provider PE4 \ : : \___ CE3 \___ PE2 . . . ............... Figure 2: Scenario 2 Kothari, et al. Expires January 7, 2010 [Page 5] Internet-Draft VPLS Multi-homing July 2009 2.2. VPLS Multi-homing Considerations The first (perhaps obvious) fact about a multi-homed VPLS CE, such as CE1 in Figure 1 is that if CE1 is an Ethernet switch or bridge, a loop has been created in the customer VPLS. This is a dangerous situation for an Ethernet network, and the loop must be broken. Even if CE1 is a router, it will get duplicates every time a packet is flooded, which is clearly undesirable. The next is that (unlike the case of IP-based multi-homing) only one of PE1 and PE2 can be actively sending traffic, either towards CE1 or into the SP cloud. That is to say, load balancing techniques will not work. All other PEs MUST choose the same designated forwarder for a multi-homed site. Call the PE that is chosen to send traffic to/from CE1 the "designated forwarder". In Figure 2, CE1 and CE4 must be dealt with independently, since CE1 is dual-homed, but CE4 is not. Kothari, et al. Expires January 7, 2010 [Page 6] Internet-Draft VPLS Multi-homing July 2009 3. Multi-homing Operation This section describes procedures for electing a designated forwarder among the set of PEs that are multi-homed to a customer site. The procedures described in this section are applicable to BGP based VPLS, LDP based VPLS or a VPLS that contains a mix of both BGP and LDP signaled PWs. 3.1. Provisioning Model Figure 1 shows a customer site, CE1, multi-homed to two VPLS PEs, PE1 and PE2. In order for all VPLS PEs within the same VPLS domain to elect one of the multi-homed PEs as the designated forwarder, an indicator that the PEs are multi-homed to the same customer site is required. This is achieved by assigning the same multi-homed site ID (MH-Site-ID) on PE1 and PE2 for CE1. When remote VPLS PEs receive NLRI advertisement from PE1 and PE2 for CE1, the two NLRI advertisements for CE1 are identified as candidates for designated forwarder selection due to the same MH-Site-ID. Thus, same MH-Site-ID SHOULD be assigned on all VPLS PEs that are multi-homed to the same customer site. Note that a VE-ID=0 or MH-Site-ID=0 is invalid and a PE should only discard such an advertisement. 3.2. Multi-homing NLRI Section 3.2.2 in [RFC4761] describes the encoding of VPLS BGP NLRI. For multi-homing operation, the same NLRI is used for identifying the multi-homed customers sites. VE ID is part of the VPLS NLRI. In addition, VE block offset, VE block size and label base are also encoded in the NLRI. For multi-homing operation, MH-Site-ID is encoded in the VE ID field of the NLRI. In addition, the NLRI for the MH-Site-ID SHOULD have the block offset, block size and label base as zero. Thus, the NLRI contains 2 octets indicating the length, 8 octets for Route Distinguisher, 2 octets for MH-Site-ID and 7 octets padded with zero. Figure 2 shows two customer sites, CE1 and CE4, connected to PE1 with CE1 multi-homed to PE1 and PE2. CE4 does not require special addressing being associated with the base VPLS instance identified by the VSI-ID for LDP VPLS and VE-ID for BGP VPLS. However, CE1 which is multi-homed to PE1 and PE2 requires configuration of MH-Site-ID and both PE1 and PE2 SHOULD assign the same MH-Site-ID and the NLRI SHOULD have the block offset, block size and label base as zero. It is valid to have non-zero block offset, block size and label base in the VPLS NLRI for a multi-homed site. However, multi-homing Kothari, et al. Expires January 7, 2010 [Page 7] Internet-Draft VPLS Multi-homing July 2009 operations in such a case are outside the scope of this document. 3.3. VPLS Preference When multiple PEs are assigned the same site ID for multi-homing, it is often desired to be able to control the selection of a particular PE as the designated forwarder. A VE preference is introduced in this document that can be used to accomplish this. A VE preference indicates a degree of preference for a particular customer site. Absence of this preference will still elect a designated forwarder based on the algorithm explained in Section 3.4. Section 3.2.4 in [RFC4761] describes the Layer2 Info Extended Community that carries control information about the pseudowires. The last two octets that were reserved now carries VE preference as shown in Figure 3. +------------------------------------+ | Extended community type (2 octets) | +------------------------------------+ | Encaps Type (1 octet) | +------------------------------------+ | Control Flags (1 octet) | +------------------------------------+ | Layer-2 MTU (2 octet) | +------------------------------------+ | VE Preference (2 octets) | +------------------------------------+ Figure 3: Layer2 Info Extended Community A VE preference is a 2-octets unsigned integer. A value of zero indicates absence of VE preference and is not a valid preference value. This interpretation is required for backwards compatibility. Implementations using Layer2 Info Extended Community as described in (Section 3.2.4) [RFC4761] MUST set the last two octets as zero since it was a reserved field. 3.4. Designated Forwarder Election BGP-based multi-homing for VPLS relies on BGP DF election and VPLS DF election. The net result of doing both BGP and VPLS DF election is that of electing a single designated forwarder (DF) among the set of PEs to which a customer site is multi-homed. All the PEs that are Kothari, et al. Expires January 7, 2010 [Page 8] Internet-Draft VPLS Multi-homing July 2009 elected as non-designated forwarders MUST keep their attachment circuit to the multi-homed CE in blocked status (no forwarding). In order to explain how these two DF election algorithms work, one must refer to the format of the VPLS NLRI. In addition to what is carried in the NLRI, a VPLS advertisement contains some attributes, such as Local Preference (LP) that are used in DF election algorithm. A VPLS advertisement might contain a Route Origin Extended Community (RO) (see section Section 4). Finally, the VPLS domain (DOM) is needed; this is not carried explicitly in a VPLS advertisement, but is derived, typically from BGP policies applied on Route Targets carried in the advertisement. In addition to these fields in the advertisement, there are three derived fields called AC-Status, PE-ID and PREF. The following are the three entities that are used in DF tie-breaking rules. 1. AC-Status (ACS): This indicates the attachment circuit status. ACS = 1 indicates that attachment circuit is down and ACS = 0 indicates that attachment circuit is up. 2. PREF: This indicates the PE preference. 3. PE-ID: This indicates the loopback address of the PE that originated the NLRI. The following sections describe the formats of the VPLS NLRI and specifies what constitutes a prefix for DF election algorithm. In addition, the derivation of the three entities used in DF election algorithm are described. 3.4.1. BGP Advertisement for VPLS Multi-homing The VPLS NLRI as described in Section 3.2.2 in [RFC4761] contains Route Distinguisher, VE-ID, VE Block Offset, VE Block Size, Label Base. These components are referred as RD, VE-ID, VBO, VBS and LB, respectively. In addition, a VPLS advertisement in case of BGP based VPLS contains control flag (CF) and VE Preference (VP). 'D' bit in the control flags is described in [I-D.kothari-l2vpn-auto-site-id]). CF:D refers to the value of the 'D' bit in the control flags. As explained in Section 3.2, MH-Site-ID is encoded as VE-ID. However, for purposes of explaining path selection rules for VPLS NLRIs, this section uses VE-ID to refer to site ID and does not differentiate a MH NLRI from a non-MH NLRI that contains non-zero block offset, block size and label base in the VPLS NLRI. Kothari, et al. Expires January 7, 2010 [Page 9] Internet-Draft VPLS Multi-homing July 2009 Table 1 shows how to set the value of ACS. Table 2 shows how to set the value of PREF based on VP and LP. The Table 3 shows how to set the value of PE-ID. +--------------------+-----+ | Control Flags (CF) | ACS | +--------------------+-----+ | CF:D = 1 | 1 | | | | | CF:D = 0 | 0 | +--------------------+-----+ Table 1 +-------------+-------------+---------------+-----------------------+ | Valid | Valid | Valid values | Comment | | values for | values for | for PREF | | | VP | LP | | | +-------------+-------------+---------------+-----------------------+ | 0 | 0 | 0 | malformed | | | | | advertisement, unless | | | | | CF:D=1 | | | | | | | 0 | 1 to | LP | backwards | | | (2^16-1) | | compatibility | | | | | | | 0 | 2^16 to | (2^16-1) | backwards | | | (2^32-1) | | compatibility | | | | | | | >0 | LP same as | VP | Implementation | | | VP | | supports VP | | | | | | | >0 | LP != VP | 0 | malformed | | | | | advertisement | +-------------+-------------+---------------+-----------------------+ Table 2 Kothari, et al. Expires January 7, 2010 [Page 10] Internet-Draft VPLS Multi-homing July 2009 +---------+---------------+-----------------------------------------+ | RO | PE-ID | Comment | | Present | | | +---------+---------------+-----------------------------------------+ | Yes | Global | Source PE as specified in RO | | | Administrator | | | | sub-field of | | | | RO | | | | | | | No | BGP | Source PE as specified by BGP | | | Identifier | Identifier. If a route carries the | | | | ORIGINATOR_ID attribute, then the | | | | ORIGINATOR_ID SHOULD be treated as the | | | | BGP Identifier of the BGP speaker that | | | | has advertised the route. | +---------+---------------+-----------------------------------------+ Table 3 Taken all together, this yields: 3.4.1.1. BGP DF Election An advertisement ADV = is discarded if DOM is not of interest to the BGP speaker. Otherwise, ADV is put into the bucket for . In other words, the information in BGP DF election consists of and only advertisements with exact same are candidates for DF election. 3.4.1.2. VPLS DF Election An advertisement ADV = is discarded if DOM is not of interest to the VPLS PE. Otherwise, ADV is put into the bucket for . In other words, all advertisements for a particular VPLS domain that have the same VE-ID are candidates for VPLS DF election. Kothari, et al. Expires January 7, 2010 [Page 11] Internet-Draft VPLS Multi-homing July 2009 3.4.2. Tie-breaking Rules This section describes the tie-breaking rules for both LDP based VPLS using BGP-AD and BGP based VPLS. Both BGP and VPLS DF election algorithms are described in two stages. For each algorithm, the first stage divides all received VPLS advertisements into buckets of relevant and comparable advertisements. In this stage, advertisements may be discarded as not being relevant to DF election. The second stage picks a single "winner" from each bucket by repeatedly applying a tie-breaking algorithm on a pair of advertisements from that bucket. The tie-breaking rules are such that the order in which advertisements are picked from the bucket does not affect the final result. Note that this is a conceptual description of the process; an implementation MAY choose to realize this differently as long as the semantics are preserved. Given two advertisements ADV1 and ADV2, the following tie-breaking rules MUST be applied in the given order. 1. if (ACS1 != 1) AND (ACS2 == 1) ADV1 wins; stop if (ACS1 == 1) AND (ACS2 != 1) ADV2 wins; stop else continue 2. if (PREF1 > PREF2) AD1 wins; stop; else if (PREF1 < PREF2) AD2 wins; stop; else continue 3. if (PE-ID1 < PE-ID2) AD1 wins; stop; else if (PE-ID1 > PE-ID2) AD2 wins; stop; else AD1 and AD2 are from the same VPLS PE; For BGP DF election, if there is no winner and AD1 and AD2 are from the same PE, BGP DF election should simply consider this as an update. For VPLS DF election, if there is no winner and AD1 and AD2 are from the same PE, a VPLS PE MUST retain both AD1 and AD2. Note that if an advertisement has VE-ID = 0, it MUST be discarded. For VPLS NLRIs, the above rules supercede the tie breaking rules described in (Section 9.1.2.2) [RFC4271] 3.4.3. DF Election on PEs DF election algorithm MUST be run by all multi-homed VPLS PEs. In addition, egress PEs SHOULD also run the DF election algorithm. As a result of the DF election, multi-homed PEs that lose the DF election Kothari, et al. Expires January 7, 2010 [Page 12] Internet-Draft VPLS Multi-homing July 2009 for a MH-Site-ID MUST put the ACs associated with the MH-Site-ID in non-forwarding state. DF election result on the egress PEs can be used in traffic forwarding decision. Figure 2 shows two customer sites, CE1 and CE4, connected to PE1 with CE1 multi-homed to PE1 and PE2. If PE1 is the designated forwarder for CE1, based on the DF election result, PE3 can chose to not send unknown unicast and multicast traffic to PE2 as PE2 is not the designated forwarder for any customer site and it has no other single homed sites connected to it. Kothari, et al. Expires January 7, 2010 [Page 13] Internet-Draft VPLS Multi-homing July 2009 4. Use of Route Origin Extended Community Due to lack of information about the PEs that originate the VPLS NLRIs in inter-AS operations, Route Origin Extended Community [RFC4360] is used to carry the source PE's IP address. To use Route Origin Extended Community for carrying the originator VPLS PE's loopback address, the type field of the community MUST be set to 0x01 and the Global Administrator sub-field MUST be set to the PE's loopback IP address. Kothari, et al. Expires January 7, 2010 [Page 14] Internet-Draft VPLS Multi-homing July 2009 5. BGP based VPLS This section describes the VPLS operations that pertain to BGP VPLS as described in [RFC4761]. 5.1. BGP Local Preference Section 3.5 in [RFC4761] describes the use of BGP Local Preference in path selection to choose a particular NLRI, where Local Preference indicates the degree of preference for a particular VE. The use of Local Preference is inadequate when VPLS PEs are spread across multiple ASes as Local Preference is not carried across AS boundary. For backwards compatibility, if VE preference as described in Section 3.3 is used, then BGP Local Preference MUST be set to the value of VE preference. Note that a Local Preference value of zero for a VE is not valid unless 'D' bit in the control flags is set (see [I-D.kothari-l2vpn-auto-site-id]). In addition, Local Preference value greater than or equal to 2^16 for VPLS advertisements is not valid. 5.2. Multi-AS VPLS Section 3.4 in [RFC4761] describes three methods (a, b and c) to connect sites in a VPLS to PEs that are across multiple AS. Since VPLS advertisements in method (a) do not cross AS boundaries, multi- homing operations for method (a) remain exactly the same as they are within as AS. However, both for method (b) and (c), VPLS advertisements do cross AS boundary. This section describes the VPLS operations for method (b) and method (c). Consider Figure 4 for inter-AS VPLS with multi-homed customer sites. Kothari, et al. Expires January 7, 2010 [Page 15] Internet-Draft VPLS Multi-homing July 2009 5.2.1. Inter-AS Method (b): EBGP Redistribution of VPLS Information between ASBRs AS1 AS2 ........ ........ CE2 _______ . . . . ___ PE1 . . PE3 --- CE3 / : . . : __/ : : : : CE1 __ : ASBR1 --- ASBR2 : \ : : : : \___ PE2 . . PE4 ---- CE4 . . . . ........ ........ Assume VE IDs to be: CE1: 1 CE2: 2 CE3: 3 CE4: 4 Figure 4: Inter-AS VPLS A customer has four sites, CE1, CE2, CE3 and CE4. CE1 is multi-homed to PE1 and PE2 in AS1. CE2 is single-homed to PE1. CE3 and CE4 are also single homed to PE3 and PE4 respectively in AS2. After running DF election algorithm, all four VPLS PEs must elect the same set of designated forwarder for all customer sites. Since BGP Local Preference is not carried across AS boundary, VE preference as described in Section 3.3 MUST be used for carrying site preference in inter-AS VPLS operations. As explained in (Section 3.4.2) [RFC4761], ASBR1 will send a VPLS NLRI received from PE1 to ASBR2 with new labels and itself as the BGP nexthop. ASBR2 will send the received NLRI from ASBR1 to PE3 and PE4 with new labels and itself as the BGP nexthop. Since VPLS PEs use BGP Local Preference in DF election, for backwards compatibility, ASBR2 MUST set the Local Preference value in the VPLS advertisements it sends to PE3 and PE4 to the VE preference value contained in the VPLS advertisement it receives from ASBR1. ASBR1 MUST do the same for the NLRIs it sends to PE1 and PE2. If ASBR1 receives a VPLS advertisement without a valid VE preference from a PE within its AS, then ASBR1 MUST set the VE preference in the advertisements to the Local Preference value before sending it to ASBR2. Similarly, ASBR2 Kothari, et al. Expires January 7, 2010 [Page 16] Internet-Draft VPLS Multi-homing July 2009 must do the same for advertisements without VE Preference it receives from PEs within its AS. Thus, in method (b), ASBRs MUST update the VE and Local Preference based on the advertisements they receive either from an ASBR or a PE within their AS. In Figure 4, PE1 will send the VPLS advertisements with Route Origin Extended Community containing its loopback address. PE2 will do the same. Even though PE3 receives the VPLS advertisements for VE ID 1 and 2 from the same BGP nexthop, ASBR2, the source PE address contained in the Route Origin Extended Community is different for the CE1 and CE2 advertisements, and thus, PE3 creates two PWs, one for CE1 (for VE ID 1) and another one for CE2 (for VE ID 2). 5.2.2. Method (c): Multi-Hop EBGP Redistribution of VPLS Information between ASes In this method, there is a multi-hop E-BGP peering between the PEs or Route Reflectors in AS1 and the PEs or Route Reflectors in AS2. There is no VPLS state in either control or data plane on the ASBRs. The multi-homing operations on the PEs in this method are exactly the same as they are in intra-AS scenario. However, since Local Preference is not carried across AS boundary, the translation of LP to VP and vice versa MUST be done by RR, if RR is used to reflect VPLS advertisements to other ASes. This is exactly the same as what a ASBR does in case of method (b). A RR must set the VP to the LP value in an advertisement before sending it to other ASes and must set the LP to the VP value in an advertisement that it receives from other ASes before sending to the PEs within the AS. Kothari, et al. Expires January 7, 2010 [Page 17] Internet-Draft VPLS Multi-homing July 2009 6. MAC Flush Operations In a service provider VPLS network, customer MAC learning is confined to PE devices and any intermediate nodes, such as a Route Reflector, do not have any for state for MAC addresses. Topology changes either in the service provider's network or in customer's network can result in the movement of MAC addresses from one PE device to another. Such events can result into traffic being dropped due to stale state of MAC addresses on the PE devices. Age out timers that clear the stale state will resume the traffic forwarding, but age out timers are typically in minutes, and convergence of the order of minutes can severely impact customer's service. To handle such events and expedite convergence of traffic, flushing of affected MAC addresses is highly desirable. This section describes the scenarios where VPLS flush is desirable and the specific VPLS Flush TLVs that provide capability to flush the affected MAC addresses on the PE devices. All operations described in this section are in context of a particular VPLS domain and not across multiple VPLS domains. Mechanisms for MAC flush are described in [I-D.kothari-l2vpn-vpls-flush] for BGP based VPLS and in [RFC4762] for LDP based VPLS. 6.1. MAC List FLush If multiple customer sites are connected to the same PE, PE1 as shown in Figure 2, and redundancy per site is desired when multi-homing procedures described in this document are in affect, then it is desired to flush just the relevant MAC addresses from a particular site when the site connectivity is lost. To flush particular set of MAC addresses, a PE SHOULD originate a flush message with MAC list that contains a list of MAC addresses that needs to be flushed. In Figure 2, if connectivity between CE1 and PE1 goes down and if PE1 was the designated forwarder for CE1, PE1 SHOULD send a list of MAC addresses that belong to CE1 to all its BGP peers. It is RECOMMENDED that in case of excessive link flap of customer attachment circuit in a short duration, a PE should have a means to throttle advertisements of flush messages so that excessive flooding of such advertisements do not occur. 6.2. Implicit MAC Flush When a connectivity to a customer site is lost, remote PEs learn that a particular site is no longer reachable. In case of BGP based VPLS, Kothari, et al. Expires January 7, 2010 [Page 18] Internet-Draft VPLS Multi-homing July 2009 a PE either withdraws the VPLS NLRI that it previously advertised for the site or it sends a BGP update message for the site's VPLS NLRI with the 'D' bit set. In case of LDP based VPLS, a PE either withdraws the PW label previously advertised or sends a PW Status TLV with appropriate status bits. If a remote PE detects that a multi-homed PE has transitioned from being a DF to a non-DF, then the remote PE can choose to flush all MAC addresses that it learned from the multi-homed PE. Kothari, et al. Expires January 7, 2010 [Page 19] Internet-Draft VPLS Multi-homing July 2009 7. Backwards Compatibility No forwarding loops are formed when PEs or Route Reflectors that do not support procedures defined in this section co exist in the network with PEs or Route Reflectors that do support. 7.1. BGP based VPLS As explained in this section, multi-homed PEs to the same customer site MUST assign the same MH-Site-ID and SHOULD contain the block offset, block size and label base as zero. Egress PEs that lack support of multi-homing operations specified in this document will fail to create any PWs for the multi-homed MH-Site-IDs due to the label value of zero and thus, the multi-homing NLRI should have no impact on the operation of egress VPLS PEs that lack support of multi-homing operations specified in this document. 7.2. BGP Auto-discovery with LDP for signaling TBD. Kothari, et al. Expires January 7, 2010 [Page 20] Internet-Draft VPLS Multi-homing July 2009 8. Security Considerations No new security issues are introduced beyond those that are described in [RFC4761]. Kothari, et al. Expires January 7, 2010 [Page 21] Internet-Draft VPLS Multi-homing July 2009 9. IANA Considerations At this time, this memo includes no request to IANA. Kothari, et al. Expires January 7, 2010 [Page 22] Internet-Draft VPLS Multi-homing July 2009 10. Acknowledgments The authors would like to thank Yakov Rekhter, Nischal Sheth, and Mitali Singh for their insightful comments and probing questions. Kothari, et al. Expires January 7, 2010 [Page 23] Internet-Draft VPLS Multi-homing July 2009 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, January 2007. [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006. [RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006. [I-D.ietf-l2vpn-signaling] Rosen, E., "Provisioning, Autodiscovery, and Signaling in L2VPNs", draft-ietf-l2vpn-signaling-08 (work in progress), May 2006. [I-D.kothari-l2vpn-vpls-flush] Kothari, B. and R. Fernando, "VPLS Flush in BGP-based Virtual Private LAN Service", draft-kothari-l2vpn-vpls-flush-00 (work in progress), October 2008. [I-D.kothari-l2vpn-auto-site-id] Kothari, B., Kompella, K., and T. IV, "Automatic Generation of Site IDs for Virtual Private LAN Service", draft-kothari-l2vpn-auto-site-id-01 (work in progress), October 2008. [I-D.ietf-pwe3-redundancy-bit] Muley, P., Bocci, M., and L. Martini, "Preferential Forwarding Status bit definition", draft-ietf-pwe3-redundancy-bit-01 (work in progress), September 2008. 11.2. Informative References [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, February 2006. [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, February 2006. Kothari, et al. Expires January 7, 2010 [Page 24] Internet-Draft VPLS Multi-homing July 2009 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, April 2006. [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, January 2007. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. Kothari, et al. Expires January 7, 2010 [Page 25] Internet-Draft VPLS Multi-homing July 2009 Authors' Addresses Bhupesh Kothari Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: bhupesh@juniper.net Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: kireeti@juniper.net Wim Henderickx Alcatel-Lucent Email: wim.henderickx@alcatel-lucent.be Florin Balus Alcatel-Lucent Email: florin.balus@alcatel-lucent.com Kothari, et al. Expires January 7, 2010 [Page 26]