Ethernet & ISDN link failover

Unanswered Question
Jul 28th, 2009

Dear All,

We are going to have a new setup where in we have one IPLC ethernet link from our location to another location and ISDN link as backup. Since ethernet interface never go down(always show up) when the connectivity loses to the other end whats the method can be used for automatic failover.

Is there any we can automatically detect the link down and make the isdn firing.

Can anyone help me on this

Thanks in advance


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (2 ratings)
vigleik Tue, 07/28/2009 - 23:56

Object tracking is supported by IOS and ASA. I will test this myself soon.

More info here, for IOS:

In this document I have some trouble understanding the "set interface" command of the route map. Seems to me it will send all icmp echo packets out the backup interface.

Shibu1978 Wed, 07/29/2009 - 23:29


Thanks for the reply.

We have cisco router 3800 series with IOS Version 12.3(11)T8 in place.

We have now 2 link terminated on the router for our HO-branch office connectivity. One being Ethernet and other being ISDN. we decided to keep Ethernet as Primary and ISDN as backup.

we are going to have static route for this connectivity.

Is there any Sample configuration which helps automatic redundancy between these links using static route.please provide the sample confguration which suite to our Router IOS version.

Thanks in advance


Sushil Kumar Katre Thu, 07/30/2009 - 01:02

Hi Shibu,

The best way to do this is to use Static Route with object tracking.

Since your primary link is ethernet based, your router will never come to know that the link has gone down unlike serial connectivities.

So you make the router aware of this using SAA probes, which will keep sending packets to the remote site and after missing few packets it will mark the link down.

Associating this with the static routes will help you make the primary route unavailable when the link fails and secondary route (with higher AD) will be available.

Refer to the link provided above and you'll get a fair idea how to configure this.

-> Sushil

Amit Singh Thu, 07/30/2009 - 01:24

Hi Shibu,

Please find a sample config attached for static route object tracking. This should solve your purpose. You might need to upgrade the IOS to 12.4 mainline to get some of the commands working for you.

Let me know if you have any questions.


-amit singh

Shibu1978 Thu, 07/30/2009 - 01:39

Hi Amit,

Thanks a lot for the configs... meanwhile my management wont allow me to upgrade the IOS due to some internal issues. can i still manage this configuration using my current IOS Version 12.3(19).

Thanks for your reply.

Amit Singh Thu, 07/30/2009 - 02:24

Hi Shibu,

IP SLA command line were intorduced with 12.4 mainline IOS.

You can still use the same feature set but the commands might be a little different. Please use the " rtr " command instead of IP SLA and you should be able to drive the policy for the same.


-amit singh

Sushil Kumar Katre Thu, 07/30/2009 - 02:36

Hi Shibu,

As rightly suggested by Amit, you can use the RTR commands on the IOS version which you have.

The command syntax was changed on the new IOS versions, however you can achieve what you are looking for using RTR commands as well.

-> Sushil


This Discussion