REG: BGP Backup

Unanswered Question
Aug 13th, 2008

The customer router has a two ethernet connections to two routers with same ISP. All three run in same AS. The connecitivty is via BGP nothing else. The customer router is receiving a default route from both ISP routers. It is like a backup. One router is preferred over the another using the MED received by the customer router.

The ISP routers have a serial connection out to the internet. The problem is the ISP main router serial interface (which is one of the customer router is connected) keep flapping. The customer router connection to the ISP routers are stable becuase of ethernect connection. Now I need somekind of solution that if the ISP router serial link is flapping We can control the customer router to switching back to the ISP main router till the link is stable.

I was thinking using Route dampening but it is not goona help becuase we are receiving only one default route.

Hope you guys can under stand what I am tyring to say here.


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rajivrajan1 Sat, 08/16/2008 - 02:07

IP SLA may help you also.

Here's how to do it

ip sla 1 < The number 1 here is arbitrary, used only to identify this sla. It is otherwise knows as the operation number>

icmp-echo< is a ISPs WAN interface that responds to pings out on the internet>

timeout 500 < This is how long to wait for a response from the ping>

frequency 3 < This is the repeat rate for the SLA>

ip sla schedule 1 start-time now life forever < This command says "start SLA 1 now and keep it running forever>

track 1 rtr 1 reachability < This comand creates the track object "1" and monitors the SLA 1>

now for the routing, we need to change the default route and associate it with the tracker

and then put it back with the tracking

ip route x.x.x.x track 1

Then we need to add our secondary route

ip route x.x.x.x 10

Now when the ping to fails the primary route is removed and the secondary route with the higher metric becomes the default. The route will be reinstated when the connectivity is restored.

Here is the reference to the Cisco IP SLA documentation


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