One document matched: draft-hlmu-l2vpn-bgp-discovery-01.txt

Differences from draft-hlmu-l2vpn-bgp-discovery-00.txt




   L2VPN Working Group                                   Paul Unbehagen 
   Internet Draft                                         Praveen Muley 
   Expiration Date: February 2005                        Vasile Radoaca 
   Document: draft-hlmu-l2vpn-bgp-discovery-01.txt      Nortel Networks 
                                                                        
   Chitanya Kodeboyina                                        Sue Hares 
   Juniper                                                     Next Hop 
                                                                        
   Peter Busschbach                                             Wei Luo 
   Lucent                                                  Cisco Sytems 
                                                                        
                                                           October 2004 
    
    
                    BGP-based Auto-Discovery for L2VPNs  
                                      
                                      
    
    
Status of this Memo 
    
   This document is an Internet-Draft and is in full conformance with 
   all provisions of Section 10 of RFC2026 [i].By submitting this 
   Internet-Draft, I certify that any applicable patent or other IPR 
   claims of which I am aware have been disclosed, or will be disclosed, 
   and any of which I become aware will be disclosed, in accordance with 
   RFC 3668.  
    
   Internet-Drafts are working documents of the Internet Engineering 
   Task Force (IETF), its areas, and its working groups.  Note that      
   other groups may also distribute working documents as Internet-Drafts. 
    
   Internet-Drafts are draft documents valid for a maximum of six months 
   and may be updated, replaced, or obsoleted by other documents at any 
   time.  It is inappropriate to use Internet-Drafts as reference 
   material or to cite them other than as "work in progress." 
    
   The list of current Internet-Drafts can be accessed at 
   http://www.ietf.org/ietf/1id-abstracts.txt 
    
   The list of Internet-Draft Shadow Directories can be accessed at 
   http://www.ietf.org/shadow.html 
    
Copyright Notice 
    
   "Copyright (C) The Internet Society (2004).  This document is subject 
   to the rights, licenses and restrictions contained in BCP 78, and 
   except as set forth therein, the authors retain all their rights." 
    
   "This document and the information contained herein are provided on 
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE 
   INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR 
   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 
 
 
Abstract 
    
   This document defines a mechanism of using BGP for the discovery of 
   L2VPN membership information. The L2VPN membership information can be 
   used by a L2VPN signaling protocol to set up pseudowires for L2VPNs, 
   such as VPWS and VPLS. 
    
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 RFC2119. 
    
    
Table of Contents 
    
   1. Introduction...................................................2 
   2. Auto-Discovery Overview........................................3 
      2.1 Assumptions................................................3 
      2.2 Reference Model............................................3 
   3. BGP Protocol Details...........................................4 
      3.1 Overview...................................................4 
      3.2 AFI/SAFI encoding..........................................5 
      3.3 NLRI Encodings.............................................5 
      3.4 Capabilities Advertisement for L2VPN Auto-Discovery........6 
      3.5 Use of RT for Auto-Discovery...............................6 
      3.6 Use of RT for L2VPN Topology...............................6 
   4. Inter-AS Auto-Discovery........................................7 
      4.1 Proxy Mode.................................................8 
      4.2 Transparent Mode...........................................8 
   5. Forwarder Removal..............................................9 
   6. Security Considerations........................................9 
   7. RD Value Selection............................................10 
   8. Dynamic Signaling Session Creation............................10 
   9. References....................................................11 
   10. Acknowledgments..............................................12 
   11. AuthorÆs Addresses...........................................12 
    
    
1.   Introduction 
    
   L2VPN signaling protocols described in [L2VPN-SIG] specify the 
   signaling procedures to set up various L2VPN models as defined in 
   [L2VPN-FRAME]. This document describes an auto-discovery mechanism 
   for the L2VPN membership information that is needed in order to 
   initiate the signaling process.  For  each  VPN, the  membership  
   information  consists  of the  set  of Forwarders, an  identifier for 
   each  Forwarder, the IP address  of each Forwarder's PE, and  any 
   other information which is  needed in order to initiate the signaling 
   procedures. This information is encoded and distributed to other PEs 
   through BGP update messages with support for both Generalized ID (GID) 
   and Psuedowire ID (PW-id) FECs. 
    
2.   Auto-Discovery Overview 
    
   [BGP-AUTO] describes the general framework of using BGP for auto-
   discovery of both L2VPNs and L3VPNs using BGP. The auto-discovery 
   mechanism specified in this document is built on this framework, and 
   the VPN membership information obtained through this mechanism can be 
   used by L2VPN signaling protocols, such as LDP or L2TP.   In order to 
   participate in the auto-discovery process, the PEs must support 
   Multi-Protocol BGP [MPBGP] and BGP Capabilities Advertisement [BGP-
   DYNCAP]. 
    
   The BGP-AD process is used to automate the provisioning aspects of a 
   VPN, in order to automate the signaling process.  Hence the use of 
   BGP is for the announcement and/or deletion of a VPN on a PE.  Once a 
   L2VPN is torn down, then BGP should remove all L2VPN membership 
   information from all other PEs. 
    
2.1    Assumptions 
    
   It is assumed that the PEÆs that participate in the auto-discovery 
   process have the capability of using BGP peerings supporting MP-BGP 
   and open capability negotiations.  The BGP-AD exchange messages 
   contain the information that is needed for LDP signaling, called 
   L2VPN membership information [L2VPN-MI]. 
    
      As such for GID: AGI, AII, PE-id 
      And for PW-id: PW-type, PW-id, PE-id 
    
   It is also assumed that multiple topologies need to be supported such 
   as a single AS, multiple AS, multiple SP, and a hierarchical model 
   with access networks and a BGP core.  This document is currently 
   focusing on the first two cases. 
    
   Besides the function of auto-discovery an additional service is 
   creating multiple L2VPN topologies such as point to point, point to 
   multipoint, and multipoint to multipoint L2VPNS. 
    
    
2.2    Reference Model 
    
   The following diagram shows an example of an L2VPN that uses BGP 
   auto-discovery. Each PE can communicate with one another through BGP 
   sessions that are established either directly between PEs or by the 
   way of route reflectors. The BGP sessions are used to advertise L2VPN 
   membership information among the PEs. Once PEs learn such information, 
   they can establish L2VPN signaling connections and pseudowires 
   accordingly. 
    
                      PE-1                        PE-2  
               +-------------+             +--------------+  
   +--------+  | +---------+ |             | +----------+ | +--------+ 
   |  VPN-A |  | |         | |             | |          | | |  VPN-A | 
   |  Site1 |--| |Forwarder| |   BGP VPN   | |Forwarder | |-|  site2 | 
   +--------+  | |    A    | |<----------->| |    A     | | +--------+ 
               | +---------+ |  Discovery  | +----------+ |  
               |             |             |              |  
   +--------+  | +---------+ |             | +----------+ | +--------+ 
   | VPN-B  |  | |         | | +---------+ | |          | | |  VPN-B | 
   | Site1  |--| |Forwarder| |-|Backbones|-| |Forwarder | |-|  site2 | 
   +--------+  | |   B     | | +---------+ | |    B     | | +--------+ 
               | +---------+ |             | +----------+ |  
               |             |             |              |  
   +--------+  | +---------+ |             | +----------+ | +--------+ 
   | VPN-C  |  | |         | |  Signaling  | |          | | |  VPN-C |  
   | Site1  |--| |Forwarder| |<----------->| |Forwarder | |-|  site2 |  
   +--------+  | |    C    | |  Protocol   | |    C     | | +--------+  
               | +---------+ |             | +----------+ |   
               +-------------+             +--------------+  
       
   [L2VPN-SIG] specifies that each Forwarder is represented by a 
   Forwarder Identifier which is the concatenation of an Attachment 
   Group Identifier (AGI) and an Attachment Individual Identifier (AII). 
    
   To advertise a Forwarder, the AGI and AII are encoded in BGP MP-NLRI 
   fields and distributed to PEs participating in L2VPN auto-discovery. 
   All Forwarders belonging to the same L2VPN will have the same AGI. 
   When a PE receives a Forwarder advertisement through BGP, it uses the 
   AII encoded in the advertisement as the Target AII (TAII) for the 
   L2VPN signaling protocol. The Source AII (SAII) of the local 
   Forwarder is known through local configuration on the PE. When a 
   Forwarder previously advertised is removed from a PE, the PE needs to 
   withdraw the AGI and AII of this Forwarder. 
    
3.   BGP Protocol Details 
 
3.1     Overview  
    
   The BGP auto-discovery specified in this document is similar to the 
   schemes described [BGPVPN] and [LDPVPN], but further optimized. This 
   introduction provides the background on these mechanisms.    
    
   The L2VPN mechanisms have been designed to support both VPWS and VPLS 
   (normal and GVPLS). The mechanisms have been optimized to support the 
   rapid growth of either VPWS or VPLS usage.   
    
   The BGP multi-protocol attribute has the following fields [MPBGP]: 
    
      [AFI] [SAFI] [length of next hop] [next hop address] [number of 
      SNPAs] [length of SNPA1] [SNPA1][length of SNPA2] [SNPA2] ... 
      [length of SNPAn] [SNPAn] 
    
   BGP auto-discovery makes use of the coloring of routes in BGP and the 
   attachment of next hop addresses to a particular sub-network point of 
   attachment (SNPA) in the multi-protocol attribute. 
    
   The coloring of routes passed in the BGP protocol can be done by 
   associating either a BGP Community (normal [BGPCOMM] or extended 
   [BGPEXTCOMM]), and or extended information in the multi-protocol 
   Network Layer Reachability Information (NLRI).  In L3VPNs [2547bis], 
   the coloring is done via a: 
         - Route Target as an Extended Community attribute, and 
         - an AFI/SAFI pair that allows the NLRI to be encoded as  
            12 bytes with 8 byte Route Distinguisher and a 4 byte IP v4 
            address.   
         
   The encoding of the AFI/SAFI alerts the L3VPNs that this AFI/SAFI 
   pair is used for L3VPNs. 
    
   As the use of additional BGP address families has increased, there 
   have been worries that problems with one address family with affect 
   other families.  New BGP work items have been proposed to reduce the 
   "fate sharing" between different address families.  These proposed 
   BGP mechanisms include: route-refresh limited to a AFI-SAFI pair 
   [BGPREFRESH], bundling of AFI/SAFIs over a TCP connection [BGP-
   BUNDLE-TCP]. While proposed BGP mechanisms are under consideration of 
   the IDR group and have some deployment, these items have not been 
   approved as BGP drafts.   
    
   These mechanisms can also reduce the fate-sharing of auto-discovery 
   mechanisms for different L2VPNS.  If explosive growth occurs in 
   either the VPWS or VPLS deployments, utilizing these AFI/SAFI 
   isolation mechanisms may allow splitting of the processing of auto-
   discovery mechanisms. 
    
3.2     AFI/SAFI encoding  
      
   The AFI value of XXXX (assigned by IANA) is used for all L2VPN 
   applications referred to as the L2VPN Auto Discovery Address Family.  
    
   The SAFI value will be set the following bit pattern:  
    
            0000 00LW  -- where 
                           L is the presence of VPLS 
                           W is the presence of VPWS 
    
   Future deployments that expect either VPWS or VPLS but not both in an 
   L2VPN may set the SAFI value in the AFI/SAFI encoding to 1 for VPWS 
   or 2 for VPLS.   
    
3.3     NLRI Encodings 
    
   The encoding of the NRLI in the MP-BGP attribute is based on the 
   AFI/SAFI identifiers.  For L2VPNs, the SAFI values of 1-3 will have 
   the following NLRI encoding: 
    
      Length of NLRI in bits, NLRI field (variable length)  
    
         Where the NLRI field is further defined as: 
    
         Length of AGI (in bits), AGI (variable), 
         Length of AII (in bits), AII (variable)   
       
       
3.4     Capabilities Advertisement for L2VPN Auto-Discovery 
    
   In order for two BGP speakers to exchange L2VPN NLRI, they MUST use 
   negotiation scheme defined in [MPBGP-RFC 2842] to ensure both of them 
   capable of processing such NLRI correctly. Two BGP speakers 
   exchanging L2VPN NLRI service MAY use the dynamic capabilities 
   negotiation scheme defined utilizing the new capabilities message 
   [BGP-DYNCAP]. 
    
   With either negotiation, the peer will specify the Multi-protocol 
   Extensions (capability 1) including in the capability list the 
   AFI/SAFI pairs for L2VPNs.  As example, a BGP peer could announce in 
   the capability could specific AFI(XXX)/SAFI(1), AFI(XXX)/SAFI(2), 
   AFI/SAFI(3). 
 
3.5     Use of RT for Auto-Discovery 
    
   In order for a Layer 2 Forwarder to be discovered via the procedures 
   of this specification, it must be provisioned with a Forwarder 
   Identifier and with a Route Target (RT) Extended Communities 
   attribute.  This RT is known as the Forwarder's "Export RT".  The PE 
   which contains the forwarder will advertise an NLRI which is 
   constructed from the AGI and AII.  The RT will be transmitted as an 
   attribute of the NLRI. 
    
    
3.6     Use of RT for L2VPN Topology 
    
   The RTs are utilized in BGP to control NLRI distribution. In addition 
   to being configured with an Export RT, each Forwarder must be 
   configured with one or more Import RTs.  If a PE receives a 
   particular NLRI in the L2VPN Auto-Discovery Family, and there is no 
   RT such that (a) the RT is one of the Extended Communities attributes 
   of that NLRI, and (b) the RT is one of the Import RTs of one of the 
   PE's Forwarders, then that NLRI is filtered.  The RTs can also be 
   used as filters at intermediate BGP speakers to constrain the 
   distribution of the auto-discovery information. 
    
    
   To form a full mesh, each Forwarder is configured with the same RT 
   value for both the "export RT" and the "import RT".  This 
   distribution policy allows the Forwarders to be visible to all BGP 
   speakers having the same Route Target (Extended Community value).  
   After the all BGP peers have the Layer-2 information, they can set up 
   a full mesh of pseudowires among these Forwarders using the L2VPN 
   signaling procedures. (Note: Other BGP policy may not utilize Route 
   Targets and fully distribute the L2VPN information to all BGP 
   speakers within the full mesh.  The key is the full distribution of 
   Layer-2 endpoints to the BGP speakers setting up the full mesh.) 
    
   Sometimes, a hub-and-spoke L2VPN network is desired. This can be 
   achieved by using two different RTs for distribution processing, 
   where one stands for "hub" and the other stands for "spoke". On the 
   hub PE, the "hub" RT is assigned to local Forwarders as the "export 
   RT", and the hub PE is configured to "import" only the L2VPN NLRIs 
   that have the "spoke" RT. On the spoke PE, the "spoke" RT is assigned 
   to the local Forwarders as the "export RT", and the spoke PE is 
   configured to "import" only the L2VPN NLRIs that have the "hub" RT.  
   This distribution policy will result in (1) spoke PEs only seeing the 
   Forwarders configured on the hub PE, and (2) a hub PE seeing all 
   Forwarders configured on every spoke PE. The L2PVN signaling then 
   sets up pseudo-wires that form the hub-and-spoke topology.   
    
   A more complex topology is partial mesh topology.  The partial mesh 
   topology can be creaated by using sets of "import RTs" and "export 
   RTs" to control route distributions. 
    
4.   Inter-AS Auto-Discovery 
    
   L2VPNS can span across multiple AS domains, network regions or 
   multiple SPs. In [L2VPN-SIG] is described a model where the L2VPN PWs 
   are decomposed in multiple PWs [called Single Hop PW]. Those SH-PWs, 
   are stitched together in order to create a logical PW end to end, 
   called Multi Hop PW. 
      
   This model can be used for P2P PW or VPLS services. However, in the 
   current proposal, it's described only the P2P PW case, and the 
   Hierarchical VPLS remaining for further work. 
    
   When PEs participating in L2VPNs reside in more than one AS, the BGP 
   auto-discovery procedures need to ensure that VPN membership 
   information can be communicated across AS boundaries. Depending on 
   how Forwarders on the PEs are connected in Inter-AS L2VPNs, ABSRs 
   operate in different modes which follow different procedures for 
   L2VPN auto-discovery. 
 
                  PE-1 ----+              +---- PE-3 
                           |              | 
                           |              | 
                        ASBR-1 ------- ASBR-2 
                           |              | 
                           |              | 
                  PE-2 ----+              +---- PE-4 
    
                |<-- AS1 -->|            |<-- AS2 -->| 
    
     
4.1     Proxy Mode 
    
   Some network operators want to enforce certain policies including 
   those of L2VPNs at the AS boundaries, and they want L2VPN signaling 
   connections and pseudowires to be confined within an AS. In this mode 
   of operation, an ASBR acts as a æProxyÆ PE that establishes and 
   manages signaling connections and pseudowires to the PEs in its own 
   AS on behalf of the PEs in another AS. 
    
   Proxy mode allows a SP to bind the number of control connections.  It 
   also allows SPÆs to confine the control connections to border routers 
   and use MD5 authentication to secure the control connection. 
    
   To connect two Forwarders on PE-1 and PE-3 respectively for instance, 
   three pseudowires need to be established and spliced together: one 
   from PE-1 to ASBR-1, one from ASBR-1 to ASBR-2, and one from ASBR-2 
   to PE-3. 
    
   Prior to establishing the pseudowires, PE-1 announces its Forwarder 
   information through a BGP update message. When receiving the BGP 
   update, ASBR-1 replaces the next-hop address with its own address so 
   that the recipient of the update thinks that ASBR-1 is provisioned 
   with the Forwarder being advertised. In order to keep track of the 
   originating PE, the BGP Identifier of PE-1 is recorded in the first 
   SNPA field. ASBR-1 then announces the update to ASBR-2 with: 
      - next-hop address of ASBR-1, and 
      - SNPA1 filled with PE-1 BGP Identifier (Router-ID). 
    
   When ASBR-2 receives the update from ASBR-1, it performs the same 
   procedures as ASBR-1, so it announces the update to all PEs in AS2 
   with: 
      - next-hop address of ASBR-2, and 
      - SNPA1 with PE1 BGP Identifier (Router-ID), and 
      - SNPA2 with ASBR-1 BGP Identifier (Router-ID). 
    
   From the perspective of PE-3, the remote Forwarder advertised through 
   the update message is provisioned on ASBR-2, so PE-3 needs to set up 
   a pseudowire to ASBR-2 in order to connect to the remote Forwarder. 
    
4.2    Transparent Mode 
    
   In this mode, L2VPN signaling connections and pseudowires traverse 
   the AS boundaries and are directly established between the PEs on 
   which Forwarders are provisioned. That is, ASBRs treat pseudowires 
   transparently and do not keep any stateful information of pseudowires. 
    
   This deployment would most often be deployed within an enterprise or 
   carrier where the AS boundaries group information but do not provide 
   a hard boundary to the L2VPNs.   
    
   The ASBRs that deal with the AS confederations that replaced an IBGP 
   mesh may be a candidate to utilize the transparent mode.  It is key 
   for the deployment and management issues to understand that the ASBRs 
   that do not support L2VPN auto-discovery and are included in the 
   transparent mode: 
      -  must pass the information transparently through the router  
         without modification. 
      -  will not keep any information about the state of the pseudo- 
         wires.  
    
   The ASBR that transparently pass the information can either: 
      1) support the L2VPN AFI/SAFI but be configured not 
         to participate in the L2VPN signaling procedures, or 
    
      2) be configured to transitive MP-BGP attributes without 
         processing any MP-BGP attributes. 
    
   For example, When receiving BGP updates that contain L2VPN NLRIs from 
   PEs in AS1, ASBR-1 simply relays them to the neighboring ASBR-2 which 
   further relays them to PEs in AS2 without modification. 
    
   Besides passing the NLRIs, the transparent ASBRs also need to provide 
   Inter-AS network reachability for the PEs so that they can establish 
   L2VPN signaling connections and pseudowires to each other. 
 
   Entities utilizing the transparent mode must be careful to consider 
   all BGP issues, L2VPN signaling and policy issues.  L3VPN also 
   utilizes this transparent mode of operation [2547bis]. 
    
5.   Forwarder Removal 
   On removal of forwarder on PE will result in withdrawal of the AGI 
   using MP_UNREACH_NLRI attribute in update message in BGP. The 
   withdrawn routes encoding in MP_UNREACH_NLRI attribute is based on 
   the AFI/SAFI identifiers.  For L2VPNs, the SAFI values of 1-3 will 
   have the following NLRI encoding:  
        
         Length of withdrawn NLRI in bits, NLRI field (variable length)   
        
            Where the NLRI field is further defined as:  
     
            Length of AGI (in bits), AGI (variable) 
    
   PE MUST withdraw the previous advertisement through BGP irrespective 
   of signaling session notification of forwarder removal. 
    
    
6.   Security Considerations 
 
   For the BGP sessions used for L2VPN auto-discovery, TCP MD5 
   authentication can be utilized.  The L2VPN signaling protocols may 
   also use its native authentication mechanisms for security. For 
   example, LDP has TCP MD5 authentication as well, and L2TP has a CHAP-
   like authentication scheme. 
    
    
7.   RD Value Selection 
    
   L2VPN auto-configurations are being deployed to ease the 
   configuration burden of L2VPNs over MPLS.  In choosing an RD, it is 
   important to understand the issues between the three existing types 
   of RD values.  For ease of transition between type 0-2 RD values, it 
   may be useful to restrict the assigned number to 2 bytes.  
    
   The following is the definition of the RD bytes from [BGP2547bis]: 
     
   [type (2 octets)]  
   [Value (6 octets)] 
      type 0: [Administrator (2 octets), Assigned number (4 octets)]  
      type 1: [Administrator (4 octets), Assigned number (2 octets)] 
      type 2: [Administrator (4 octets), Assigned number (2 octets)] 
    
    
   A type 0 RD Administrator filed has two octets for an Administrator 
   value (2 bytes) that is drawn from the public autonomous system (AS) 
   number space combined with a 4 byte assigned number. Today, the AS 
   numbers fit within 2 bytes.  Within 3-7 years, the AS numbers may 
   exceed the 2 byte space, and require the 4 byte AS numbers. It would 
   be wise to only use the 2 bytes of Assigned number for type 0 and 
   type 2 assigned numbers.  Type 1 uses an assigned IP address [4 bytes] 
   as the administrator identifier.  This address in the type 1 RD 
   administrator field should utilize. 
    
   The type 1 RD administrator field an IP address is from the public IP 
   address space.  Private address numbers used for administrator 
   numbers should not be used in RDs. Use of private address numbers 
   (such as network 10) may run into collisions with two network 
   deployments using the same IP address.  
 
8.    Dynamic Signaling Session Creation 
    
   The purpose of BGP auto-configuration is to reduce the configuration 
   burden for setup of psuedowires.  In deployment of the BGP auto-
   discovery just as in the normal BGP, the policy controlling the auto-
   configuration uses configuration plus the existence of the 
   information in BGP as the impetus to establish a signaling session.   
    
   Signaling sessions MAY be established before or after the BGP auto-
   discovery phase is completed.  This can be done in two ways:  
     1. Each PE can have a signaling session manually created to all the 
        PEs participating in L2VPN in the network before the BGP auto-
        discovery, regardless of whether they have any forwarders in 
        common or not OR 
     2. Each PE can set up a session to other PEs dynamically as the BGP 
        auto-discovery phase progresses if they have at least one 
        forwarder in common after the auto-discovery phase is complete. 
    
   Approach (1) has the benefit of simplicity and pre-determined 
   behavior in that the L2VPN signaling sessions may not go up and down 
   depending on dynamic L2VPN memberships. 
 
   Approach (2) provides complete automatic creation of signaling 
   sessions based on the BGP auto-discovery mechanisms and local policy. 
   The benefit of this approach is that reduces the configuration burden 
   to a minimum. Once obtain L2VPN membership information through BGP 
   auto-discovery, a PE may start L2VPN signaling sessions to other PEs. 
    
   With either approach, whenever a new Forwarder is added to an L2VPN, 
   a PE MUST advertise its information to all other PEs through BGP. The 
   receiving PE may initiate a pseudowire to the advertising PE with the 
   information learnt through BGP auto-discovery. Whenever an existing 
   Forwarder is removed from an L2VPN, a PE MUST withdraw the previous 
   advertisement of this Forwarder through BGP. PEs with pseudowires 
   connecting to this Forwarder will also receive an update through the 
   signaling sessions notifying that the Forwarder is removed. 
    
   Either approach may be chosen for deployment depending on given 
   deployment requirements. 
    
9.   References 
 
   [2547bis] "BGP/MPLS VPN", Rosen, et. al., draft-ietf-l3vpn-
   rfc2547bis-01.txt, September 2003. 
    
   [BGP-AUTO] "Using BGP as an Auto-Discovery Mechanism for Network- 
      based VPNs", Ould-Brahim, et. al., draft-ietf-ppvpn-bgpvpn-auto- 
      03.txt, August 2002. 
    
   [BGP-BUNDLE-TCP], "Multisession BGP", John G. Scudder, Chandra  
            Appanna, November 2003,  
            draft-scudder-bgp-multisession-01.txt 
    
   [BGPCOMM], "BGP Communities Attribute", R. Chandra, P. P. Traina, T.  
               Li, RFC 1997, August 1996 
    
   [MPBGP]  " Multiprotocol Extensions for BGP-4", T. Bates, R. Chandra,  
            D. Katz, Y. Rekhter, draft-ietf-idr-rfc2858bis-06.txt,  
            November 2004 
 
   [BGP-DYNCAP], "Dynamic Capability for BGP-4", Enke Chen, Srihari R.  
                  Sangli, draft-ietf-idr-dynamic-cap-06.txt 
    
   [BGPEXTCOMM], "BGP Extended Communities Attribute", Srihari R. Sangli,  
                  Daniel Tappan, Yakov Rekhter, draft-ietf-idr-bgp-ext-
                  communities-07.txt, August 2003 
 
   [BGPREFRESH], "Route Refresh Capability for BGP-4", Chen E., RFC 2918,  
                  September 2000. 
    
   [BGPVPN]  "Using BGP as an Auto-Discovery Mechanism for Network-based  
               VPNs", H. Ould-Brahim et. al., draft-ietf-ppvpn-bgpvpn-
               auto-03.txt, August 2002 
    
   [VPLS-LDP] "Virtual Private LAN Services over MPLS" draft-ietf-l2vpn-
   vpls-ldp-05.txt  V.Komeplla, Marc Lasserre, February 2005 
    
   [VPLS-BGP]  "Virtual Private LAN Service", K. Kompella, Y. Rekhter, 
   draft-ietf-l2vpn-vpls-bgp-02.txt, November 2004 
                     
    
   [L2VPN-FRAME] "L2VPN Framework", Anderson, et. al., draft-ietf-l2vpn- 
               l2-framework-05.txt, December 2004. 
    
   [L2VPN-SIG] "Provisioning Models and Endpoint Identifiers in L2VPN  
               Signaling", Rosen, et. al., draft-ietf-l2vpn-signaling-
               02.txt, March 2005. 
    
   [LDPVPN]   E. Rosen, "LDP-based Signaling for L2VPNs",draft-rosen- 
              ppvpn-l2-signaling-02.txt, September 2002 
 
   [MPBGP-RFC 2842] "Multiprotocol Extensions for BGP-4", Bates, T., Y.  
               Rekhter, R. Chandra, D. Katz, RFC 2842, June 2000 
                                                        
       
   [SOFT-NOTIFY]  "BGPv4 Soft-Notification Message", Gargi Nalawade,  
                  Keyur Patel, John Scudder, David Ward, October 2003. 
 
 
 
 
 
 
10.    Acknowledgments 
   We wish to thank Hamid Ould-Brahim, Shobhan Lakkapragada, Florin 
   Balus (Nortel Networks) for their comments and contributions. 
    
11.    AuthorÆs Addresses  
 
   Susan Hares 
   Merit, Inc. 
   1071 Beal Avenue, 
   Ann Arbor,           MI 48109 
    
   Wei Luo 
   Cisco Systems, Inc. 
   170 West Tasman Drive 
   San Jose, CA 95134 
   Email: luo@cisco.com 
    
   Paul Unbehagen 
   Nortel Networks 
   35 East Davis Dr. 
   RTP, NC 27709 
   Phone: 919-905-2956 
   Email: paulu@nortelnetworks.com  
    
   Praveen Muley 
   Nortel Networks 
   600 Technology Park 
   Billerica, MA 01821 
   Phone: 978-288-3603 
   Email : pmuley@nortelnetworks.com 
    
   Vasile Radoaca 
   Nortel Networks 
   600 Technology Park 
   Billerica, MA 01821 
   Phone: (781) 856-0590/978-288-6097 
    
   Chaitanya Kodeboyina 
   Juniper Networks  
   1194 North Mathilda Ave. 
   Sunnyvale, CA 94089 
   Email: ck@juniper.net 
    
   Peter B. Busschbach   
   Lucent Technologies   
   67 Whippany Road 
   Whippany, NJ, 07981 
   Email: busschbach@lucent.com 


PAFTECH AB 2003-20262026-04-23 00:26:57