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BGP-based Auto-Discovery for L2VPNs

Learn how BGP enables Auto Discovery for LDP-based L2VPNs, including capability negotiation, MP extensions, AFI/SAFI pairs, route coloring, AGI & AII encoding, and NRLI encoding. Example scenarios and conclusion provided.

jamesdpalmer
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BGP-based Auto-Discovery for L2VPNs

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  1. BGP-based Auto-Discovery for L2VPNs

  2. Overview • Intent is to use BGP to provide an Auto-discovery method for LDP based L2VPNs. • Capability Negotiation • MP Extensions (capability 1) • And the list of AFI/SAFI pairs for L2VPNs. • i.e. AFI x / SAFI 1, AFI x / SAFI 2, AFI x / SAFI 3 • Use RT to color routes and control topology. • AGI & AII Encoded as SNPA portion of the MP_Reach_NLRI

  3. AFI/SAFI Encoding • AFI to be assigned by IANA • 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 • SAFI value is set 3 to signify that the NRLI encoding can be used for both

  4. 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)

  5. Discovery Example BGP transmit – Next Hop, AGI, & AII LDP receive – Target, AGI, SAII, TAII PE1 PE2 CE CE Next Hop RT MP_Reach_NLRI: AFI = xxxx SAFI = 0000 000W Length of NH Next Hop # SNPA’s AGI Length (bits) AGI value (variable) AII Length (bits) AII Value (variable) 3. BGP filters on RT and LDP receives the discovery message. 4. AII from the update message becomes the TAII. 1. New Forwarder created 2. BGP sends AD Update message

  6. Conclusion • Provide a method of Auto-discovery for LDP based L2VPNs • New AFI needed for L2VPNs • Works for VPWS & VPLS (distributed and Non-distributed)

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