The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] RE: mpls traceroute problems
hi i think you can toubelshoot this problem with the "mpls ip ttl-expiration pop 1" on the 7400 if you see that this command shows you the first hop then its pretty clear what happened here when a router receives a labeled packet with ttl 1 in the mpls shim header it will not send an icmp ttl exceed back to the source , but it will generate an icmp ttl exceed with the ip of the source and (the label information inside the icmp header) and then forwards this packet along the lsp to the destination of the icmp with the same labels as if the ttl wasnt 1, and then the destination will send back to the source the icmp ttl exceed.(because the ip header contains the destination of the source router) this behavior is needed in an mpls vpn implementation where the p routers dont have vpn prefixes knowledge in their routing table so they cannot return the ttl exceed to the source. in your situation i beleive that the your gsr12008 that receives a labeled packet and pops the label has a problem returning the icmp ttl exceed after you indeed see that the problem is your gsr i think the command no tag-switching ip propagate-ttl on the gsr will solve it when using the "mpls ip ttl-expiration pop 1" you tell the 7400 not to send the icmp ttl exceed along the lsp but to send it back to the source only if it has a label stack of 1 or less in this way we can make sure that it will not affect vpn traffic that have 2 labels. if you also do the "mpls ip ttl-expiration pop 1" on your gsr it will solve the problem too but it will affect your vpn traceroute because although usually vpn traffic have a label stack of 2 , in the case of inter-provider mpls you have a label stack of 2 untill the asbr , between the asbr's there is only one label. guy ----------------------------------------------------------- Guy Alexander, CCIE #8502 , JNCIS Customer Service Engineer Motorola Israel Information Systems LTD. Tel : 972-9-9606476 Mobile:972-50-331494 Fax : 972-9-9550540 ----------------------------------------------------------- ------- 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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