Re: [Isis-wg] Re: IS-IS as PE/CE routing protocol in BGP/MPLS/VPN

Stefano,

AFAIK a sham link is only required when two VPN sites that belong to the
same area share a direct backdoor link. If no backdoor link exists between
the sites then no sham link is required.

So what happens if i dont have that direct (backdoor) link between two
different VPN sites or if there is no IS-IS adjacency over that backdoor
link?

Regards,
Manav

----- Original Message ----- 
From: "stefano previdi" <[email protected]>
To: "Manav Bhatia" <[email protected]>; "lidefeng" <[email protected]>
Cc: <[email protected]>; <[email protected]>
Sent: Friday, May 16, 2003 3:15 AM
Subject: Re: [Isis-wg] Re: IS-IS as PE/CE routing protocol in BGP/MPLS/VPN

If I understand correctly the concept of the sham-link, the
PE will receive a mp-bgp route containing the other end of
the sham-link and the extComm describing it. This route need
to be the best among other (possible) mp-bgp routes (with
same RD) for the same prefix. If such route is best, then you
won't really import it into the vrf but rather you will "use
it" in order to add a (fake) adjacency into the isis lsp the
PE will originate. Then you run spf as part of the isis
instance running in the vrf and compute your routes. After
spf computation you'll find that the prefixes of the remote
site are reachable through the sham link (according to the
metric of your links of course). So I don't believe you
really need to change the bgp selection process.

Btw, I don't see any reference to TLVs 22 and 135 in the
draft...

s.