Issue on last mile connectivity on a ethernet terminated link from SP

Unanswered Question
Nov 13th, 2008

Hi Guys,

I have a Link from SP "A" which is terminated at my Ethernent interface of my router. I have configured Eigrp for this.

Issue: when i have problem with the lastmile ( 3rd/4th Hop from my eth interface)conectivity my ethernet connection will not go down ( as its next hop will be up) due which link to the SP "A" will not go down . but the traffic will not passon to the destination network.

Hence I need to manually move my traffic towards some other SP by shutting down the ethernet interface which is not a auto failure.

Expecting : I want my autofailure to work in this scneario within a span of 30-60 sec.

Please share me the instructions!

Appreciate all your early response & help.

Regards,

Akber.

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mirzaakberali Thu, 11/13/2008 - 05:14

Hi,

Can i configure Tunnel between end-end to resolve this issue.

Please suggest .

Akber.

Giuseppe Larosa Thu, 11/13/2008 - 05:23

Hello Akber,

your scenario is unclear to me.

you say you have EIGRP running on the link but that you expect the link to fails.

if a remote router fails EIGRP should be able to detect this topology change.

Or EIGRP is not running on all the path ?

if the penultimate hop router is redistributing a static route into EIGRP you can use object tracking

see

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/dot1qtnl.html

if you track ip reachability of static next-hop you can detect when it fails and then remove the static route and remove it from redistribution into EIGRP

Hope to help

Giuseppe

mirzaakberali Thu, 11/13/2008 - 07:25

Hi ,

let me add few more points here : -

Router 1 is conected to ISP A & IPS B

Active link :Router 1 to ISP A is configured with eigrp routing where router termination point is eth interface .

Standby link : Router 1 to ISP B.

Assume that Router 1 to ISP A is having 4 hops.In that if my 3rd/4th hop goes down

my ethernet int will not down but traffic suddenly stop going. eigrp will take soem amount of time to reach till 3/4th hop while returning it will identify as neighbor is down.

so i have to manually shut the my eth int and router the traffic to ISP B.

But i want to have auto failue in thsi scnerio as well.

Can i achive this by configuring tunel between end-end .

Please let me know.

Akber .

Giuseppe Larosa Thu, 11/13/2008 - 07:36

Hello Akber,

>> my ethernet int will not down but traffic suddenly stop going. eigrp will take soem amount of time to reach till 3/4th hop while returning it will identify as neighbor is down.

EIGRP has very fast convergence it supports triggered updates this is not RIP or IGRP:

it takes 15 seconds to detect neighbor is down and then updates are propagated through the net.

In 20 seconds it should provide to the first router the info the remote ip prefixes are down.

If this doesn't happen is because EIGRP is not used end-to-end or some form or redistribution and / or summarization is masking the network failure

Have you configured no auto-summary under eigrp on all routers ?

Hope to help

Giuseppe

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