[Softwires] Why RFC5512 can not be used for inter-AS softwire mesh

[xuxiaohu 41208 <[e-mail]>]

Hi all,

The abstract of RFC5512 (The BGP Encapsulation Subsequent Address Family Identifier (SAFI) and the BGP Tunnel Encapsulation Attribute) is as follows:

Abstract

   In certain situations, transporting a packet from one Border Gateway
   Protocol (BGP) speaker to another (the BGP next hop) requires that
   the packet be encapsulated by the first BGP speaker and decapsulated
   by the second.  To support these situations, there needs to be some
   agreement between the two BGP speakers with regard to the
   "encapsulation information", i.e., the format of the encapsulation
   header as well as the contents of various fields of the header.

According to RFC5512, the tunnel is started from one BGP router and terminated another (i.e. the BGP next hop), unless ensuring that an ASBR that is not an AFBR does not change the next hop of the E-IP routes (i.e., option 3 for inter-AS softwire described in Softwire Mesh Framework [RFC5565]), RFC5512 alone can not be used to support inter-AS softwire mesh.

As I mentioned during my presentation, the option 3 described in RFC5565 requires all non-AFBR ASBRs to be upgraded in order to support this capability. In contrast, our approach has not such limitation since we use a transitive Extended Community attribute to carry the tunnel endpoint address.
  
Best wishes,
Xiaohu