Hi Eric, Please see the comments in-line.
Thanks, Mingui >-----Original Message----- >From: Eric Rosen [mailto:[email protected]] >Sent: Tuesday, July 23, 2013 10:42 PM >To: Mingui Zhang >Cc: [email protected]; [email protected]; [email protected] >Subject: Re: FW: New Version Notification for >draft-zhang-l3vpn-label-sharing-00.txt > > >Eric> In Figure 2.1, you show CE2 connected to PE3 and PE4. Now suppose we >also >Eric> have CE4 connected to PE3 and PE5. If PE3 fails, one might want use PE4 >as >Eric> a backup for CE2, while using PE5 as a backup for CE4. Your scheme >doesn't >Eric> seem to handle this. > >Mingui> If PE3 and PE4 allocate (1100, vNH1) for CE2 while PE3 and PE5 >Mingui> allocate (1101, vNH2) for CE4. The scheme works well. > >Are you now suggesting to allocate a vNH address and shared label for every >CE? Since there are many more CEs than PEs, that would make the scaling >properties of the scheme a lot less favorable. That's not true. Please search the following sentence in the draft. "Egress PEs create a vNH router in IGP to represent the set of CEs dual-homed to the same egress PEs in the Service Provider's backbone." I don't think this kind of allocation bears scalability issues. > >Eric> Also, even in the case of Figure 2.1, it seems entirely possibly that >Eric> one might want PE3's primary route to CE2 to be via the directly >Eric> attached interface, while wanting PE4's primary route to CE2 to be via >Eric> PE3. Does your scheme handle this case? > >Mingui> Yes, it handles. Please see the right part of eq1: Sxy3+M. If the >Mingui> backup tunnel goes through Pxy->PE4->PE3->vNH, then Sxy3+M < = >Mingui> Sxy4+S. That means eq1 does not hold. > >I think that equation is based only on the IGP link costs. A service >provider might use BGP LOCAL_PREF to give the PE3-->CE2 route a higher >degree of preference than the PE4-->CE2 route, in which case PE4's normal >route to CE2 could be via PE3, independent of the IGP link costs. Of >course, PE4 will switch to the directly attached route when it learns, >through IGP, that PE3 is not reachable. But in that case you might not meet >the FRR goal. To achieve the goal of protection, the draft suggested the PEs in the RG use routes that they learn from the CE. If the service provider insists on using the route from just one PE, he is ready to give up the reliability that can be provided by multiple PEs.
