BGP migration interfering with previously seamless Backup ISDN failover

Answered Question
Sep 20th, 2005
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We ran and still run Eigrp. We kept a simple floating static route (AD of 120) to route IP out the Bri interface should the Primary Serial Int fail. Since the introduction of BGP (MCI Private INTERNET) our routers are essentially edge routers. When the primary interface fails on one end the Backup INt (120) routes into a "black hole of BGP" on the remote end, until of course BGP (20) can figure out the route is no longer valid. Former 2 second failover is now turning into 1:20 second failover. What direction should I be persuing before impulsively grabbing the duct tape??? Bottom line BGP is not getting the word that our Remote End has failed, while EIGRP always did this instantaneously.

Correct Answer by Harold Ritter about 11 years 11 months ago

If the interface to the SP goes down, bgp fast-external-fallover should take the BGP session down automatically. This feature is on by default.


If the interface doesn't go down then the best way to quickly detect that the peer is not responding is to lower the BGP timers (ie: timers bgp 3 9).


Hope this helps,

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Correct Answer
Harold Ritter Tue, 09/20/2005 - 07:16
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If the interface to the SP goes down, bgp fast-external-fallover should take the BGP session down automatically. This feature is on by default.


If the interface doesn't go down then the best way to quickly detect that the peer is not responding is to lower the BGP timers (ie: timers bgp 3 9).


Hope this helps,

tteslicko Tue, 09/20/2005 - 08:32
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If the interface to the SP goes down, bgp fast-external-fallover should take the BGP session down automatically. --that much is true on either or end. It is the remote end or the UNFAILED BGP side that the message is not propogating. For instance the UK fails. BGP Notifies UK PE neigbor is down. On the NY side the news of the UK side's PE neighbor is never propogated to either the NY PE or CE. Therefore the UK sends data over the backup link immediately to NY and NY replies out the now invalid BgP interface till it realizes there is no route. For well over a minute the NY data sends the UK replies into the oblivion of a failed BGP route till convergence can occur.

tteslicko Wed, 10/19/2005 - 05:36
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Final on this was I had to make sure that not only did we adjust these timers with our neighbors locally but the Providers PE to PE adjusted their neigboring timers between themselves as well..took about 3 weeks to grasp...Thanks!!

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