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New Member

Failover with 2 ISP's


Just wondering if someone knows which router will do an ISP failover. I do not want internal clients on the network to notice if one of their ISP's goes down ... ideally I would like a router to failover to a second interface ... the catch is that can these interfaces be different ... i.e. T1 and DSL or ISDN and DSL.

Thanks in advance

  • Other Network Infrastructure Subjects
New Member

Re: Failover with 2 ISP's

Any Cisco router that runs IOS can likely do what you need. Are you just running default routes to the ISPs? If so, something like this would work...

'ip route s0'

'ip route s1 200'

The s1 interface administrative distance (200) keeps it out of the picture until there are no better options. This assumes that both interfaces to both ISPs are up on a daily basis. If you need to bring an interface up from a down state to back the primary up, there is a little more (not much) to it.

New Member

Re: Failover with 2 ISP's

OK - that is great news!

The router is a 2611 with IOS 12.1(7). I believe it can handle two different types of interfaces, one being DSL - do you know? Here are our routes: is subnetted, 1 subnets

C is directly connected, Ethernet0/1

yyy.yy.y.y/30 is subnetted, 1 subnets

C yyy.yy.y.yy is directly connected, Ethernet0/0

S* is directly connected, Ethernet0/0

The plan is to run a minimal DSL as a backup to the primary 10Mb connection, and crank it up to 4Mb when needed. So it will be running simultaneaously.

So once the route of the primary is not available, all traffic will be routed to the secondary interface and all I have to do when I add the second interface is give it a greater administrative distance. That is sweet! I guess as far as the router is concerned, it doesn't care about different ISP's - it's just another network with less "priority".


New Member

Re: Failover with 2 ISP's

You have the concept down perfectly. However, I understand that it can be a challenge to get the ethernet interface to register as down when, in fact, the connection to the ISP is lost. With HDLC, PPP, etc. on serial interfaces it is pretty straight forward. Not necessarily so with static routes and ethernet interfaces. I have heard of folks getting the ISP to run an IGP protocol of some sort and then setting up dialer watch so that the dynamic route can be monitored and aged out when appropriate.

Anyone with more experience have better suggestions for Kurtis?

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