[c-nsp] OSPF + metric / cost

CiscoNSP List CiscoNSP_list at hotmail.com
Sat Feb 13 17:39:49 EST 2016

Hi Everyone - Have the following scenario:

POPA - 2 ASR1ks acting as RR's

ASR1 has a 1Gb link to POPC via POPB - POPC has IPTransit gw
ASR2 has a 1Gb link to POPD - POPD also has IPTransit gw, and a 1Gb link to POPC
ASR1+ASR2 are also directly connected

I have both IPtransit routers sending defaults to both RRs - Preference for the RRs default is POPC (Set via weight) as this gw is 2m/sec away, compared to 20m/sec to POPD.

Link from ASR2 -> POPD was unused, unless link(s) to POPB/C failed - I wanted to use this link for prefixes that were "local" to POPD....achieved this by setting a lower OSPF cost on this link....everything "appeared" to be working as I wanted (Prefixes local to POPD were now using the previously dormant link) - but this created a problem with ASR2's "preffered" path to POPC...It saw the link to POPD->POPC as the shortest path....this obviously wasnt what I wanted, as it increased latency to the Internet for any tail connected/using ASR2 (ASR1 still saw the link POPB->POPC as the "best" path)

So, Im wondering if it is possible (via OSPF?) to have ASR2 see the path to POPC as "best" via POPB, but also still utilise its direct link to POPD for local prefixes...Ive played a bit with OSPF cost, but as soon as I lower the cost from ASR2->POPD enough for it to be used for local POPD prefixes, ASR2 starts using this link to get to POPC.

Note  - OSPF is only used for loops+p-t-p link IPs, iBGP is used for all "other" prefixes

Cheers for any  suggestions.

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