The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: IGP Routes calculation over TE Tunnel
Hi Eric Thanks for the clarification ,Appreciate if U could answer the 2nd question in my initial msg : Quote >>Now : >>Config T2 from R4 to R1 with absolute metric 1 . >>R1 and R4 are config to advertise T1,T2 as link in the IGP . >> >>at R1 : could we expect that it is now case 2 ??? Unquote To use CSCO terminology this is the case of FA configured at R1 and R4 and the link cost is set to 1 in both end . what will be the RIB at R1 ,is it same as Case 2 ?? . ie: >>Case 2 : >> >>Prefix Cost Via >>P2 10 a >>P3 11 T1 >>p4 1 T1 My guess is yes , as R1 will insert R4 as one of his own neighbor (despite no real "adjacency" with R4, by "no real" i mean no IGP Hello making the adjacency ) when filling the TENT list . Brgds >From: "Eric Osborne" <eosborne@cisco.com> >To: "M. ELK" <elkou141061@hotmail.com>, mpls-ops@mplsrc.com >Subject: Re: [MPLS-OPS]: IGP Routes calculation over TE Tunnel Date: Tue, >18 May 2004 08:12:37 -0400 > >On Tue, 18 May 2004 10:41:03 +0000, M. ELK <elkou141061@hotmail.com> wrote: > >>Hi >> >>Despite it was explained to me previously still facing some difficulty. >>Consider the following : >> >> >>R1-a-----R2-----R3-----R4 >> >>P1 prefix associated with R1 ,P2 with R2 ...etc . >> >>All link with 10 as cost . "a" is the interface of R1 >> >>currently at R1 : >> >>Prefix Cost Via >>P2 10 a >>P3 20 a >>p4 30 a >> >>Set T1 from R1 to R4 with absolute metric 1 : >> >>Case 1 : >> >>Prefix Cost Via >>P2 10 a >>P3 20 a >>p4 1 T1 >> >>Case 2 : >> >>Prefix Cost Via >>P2 10 a >>P3 11 T1 >>p4 1 T1 >> >>Is it case 1 or case 2 (mainly for P3) ?? > >The details are probably going to be implementation-specific, but in the >case of the implementation I know the most about, it will be case 1. >Costs are changed *after* the IGP SPF is computed, which means that the >cost to p4 has no impact whatsoever on p2 and p3. This is, of course, >assuming you are talking about our autoroute feature. We have this other >thing, forwarding-adjacency, that doesn't behave like this at all, and >other vendors are free to do whatever they like with metrics. > >>My guess it will be case 1 to follow draft-ietf-rtgwg-igp-shortcut-00.txt > >I just looked at this draft, and it basically explains how our autoroute >works. This leads me to believe that at least one other implementation >works basically the same way. > >As an aside, the special case in section 5 of the draft looks a *lot* like >http://www/en/US/products/sw/iosswrel/ps1612/products_feature_guide09186a0080080850.html#1019729. > >>, but what are the reason >>to prefer this approach , is it to avoid any possible loop ??? If yes : >>could U pls provide an >>example of topology where loop could exist . >> > >I've not seen too many people play with autoroute metrics; they are >confusing to most people, and tend to be used to solve the last 5% or 10% >of problems after you've applied lots of other tricks. But that's just >me, others may have different exposure. > >As far as loops, in the autoroute metric case there won't be any loops, >because of where the cost adjustment is done. > > > > >eric > >>. >> >>Now : >>Config T2 from R4 to R1 with absolute metric 1 . >>R1 and R4 are config to advertise T1,T2 as link in the IGP . >> >>at R1 : could we expect that it is now case 2 ??? . >> >> >>Brgds >> >>_________________________________________________________________ >>The new MSN 8: advanced junk mail protection and 2 months FREE* >>http://join.msn.com/?page=features/junkmail >> >>------- >>The MPLS-OPS Mailing List >>Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml >>Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > > _________________________________________________________________ Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail ------- The MPLS-OPS Mailing List Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml Archive: http://www.mplsrc.com/mpls-ops_archive.shtml
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