Hi Adam Thanks for wonderfull explanation. Could you please confirm for Per Link also the condition for loop free criteria will remain same i.e N,D < N,S + S,D and in per link i'll get only link protection and if some vendor says they support node protection & link protection with node means actually they are talking for per prefix implementation.
Correct me if i am wrong. Thanks Amit Dhamija --- On Tue, 6/4/13, Adam Vitkovsky <[email protected]> wrote: > From: Adam Vitkovsky <[email protected]> > Subject: RE: [c-nsp] Difference in IP FRR Link vs Per Prefix Option > To: "'Dhamija Amit'" <[email protected]>, [email protected] > Date: Tuesday, June 4, 2013, 8:41 AM > Hi Amit, > Well I believe you can look at it as link-protection vs > node-protection. > > Per-link LFA provides only link-protection -that means > protecting node (node > computing the backup path for its primary links) will only > chose LFA > node/candidate that has a link to primary next-hop node > (node currently > acting as primary next-hop). > In other words it will compute backup path that has to end > on the same node > currently acting as primary next hop. > And as you can see this might not always be the case in your > topology as the > LFA candidate node might not have a direct link to your > primary next-hop > though it might have a link to some other upstream node > (node on a loop free > path towards the destination). > Also > Per-link is essentially per-next hop LFA (by next hop I mean > the other end > of the directly connected link) so the protecting node > computes only one > alternate/repair next hop for each primary next hop. The > consequence of this > is that all prefixes with the common primary next-hop share > also the same > backup next-hop. And there can be cases where the protecting > node would have > multiple lower BW links to one/more LFA candidate nodes, > instead of one link > with BW equal to the primary link. In such a case per-link > LFA would chose > only one of the links and in case of primary-link failure > the one lower BW > link might get congested. The congestion might as well occur > on primary and > backup link with equal BWs as the link serving as backup > might already be > carrying some level of traffic on its own and might not cope > well with the > additional load during the primary link failure. So I case > the protecting > node found more LFA candidates for a given primary next-hop > it would > consider just one of them. > > Per-prefix LFA provides node-protection that is, the > protecting node will > consider also LFA candidates that do not have a direct link > to node acting > as primary next-hop however they have a link to an upstream > node. This > increases the possibility of finding the LFA candidate(s) as > well as > provides protection in case the node currently acting as > primary next-hop > fails completely. > And > In addition to node-protection, repair node running > Per-prefix LFA computes > LFA next-hop per each prefix independently. That means if > the protecting > node finds multiple nodes qualifying as LFA candidates for a > given primary > next-hop, in case of primary next-hop failure it will > load-share the traffic > among multiple backup paths. > > > It's still morning for me so I hope it all makes some sense. > > > adam > -----Original Message----- > From: cisco-nsp [mailto:[email protected]] > On Behalf Of > Dhamija Amit > Sent: Tuesday, June 04, 2013 8:44 AM > To: [email protected] > Subject: [c-nsp] Difference in IP FRR Link vs Per Prefix > Option > > > Hi > > Can some one help me in understanding the exact difference > in IP FRR Per > Link and Per Prefix option , It's mention in some docs that > coverage of > protected prefixes will be more in per prefix option , If we > have per link > then all the prefixes learned through same link will be > covered in LFA > computation then what else is left for any router the IGP > prefixes will be > learned through some link and if link is protected means all > prefixes are > protected then how can we say coverage is more in per > prefix. > > I see some vendors Juniper , ALU doesn't supports per prefix > option.Could > you please elaborate more on this. > > Thanks for help > > Regards > Amit Dhamija > > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
