automatic switch b/w routes

Unanswered Question
Sep 5th, 2007

suppose we have two links on a 1800 series router (one) Serial and (second) fastethernet

In case the primary link fails which is serial the router should do an automatic switching for traffic b/w routes (serial to fastethernet)

therefore, is it possible and how? i am sure it is. but i need best advice. currently i have things in mind e.g IP-SLA

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4 (1 ratings)
lgijssel Wed, 09/05/2007 - 04:17

Using a routing protocol (OSPF/EIGRP) is no option for an internet line.

When you have static routes, you are stuck with using tracking (ip sla).



Richard Burts Wed, 09/05/2007 - 04:26


This discussion presumes that the router is using static routes. But perhaps we should confirm that.

If there is a primary static route which points to the serial interface (or to a next hop which is reached over the serial interface) and if the serial interface is a point to point connection (HDLC, or PPP, or Frame Relay point to point subinterface) then if the link fails the static route will be removed from the routing table. This would mean that a floating static route pointed to the FastEthernet should work ok.

You can use Object Tracking or SLA if you want to be sure, but these technologies were developed for environments where the primary static route was over a LAN type interface (or some multipoint serial) where the interface will remain protocol up even when you lose connectivity over the interface.



zulqurnain Wed, 09/05/2007 - 21:23

thanks for the valuable input,

yes there will be a primary static route pointing to serial int and serial is point 2 point (PPP).

therefore, u are suggesting that i should go for having floating static route pointing to fastethernet.

since IP-SLA will not work for my setup, is there any other way of doing it. like e.g. i read one scanrio that if i have 2 EIGRP running on the same router with (backup route) having higher distance i can achieve the desired results, now i didn't try it yet but would really like to have your opinion on it.

Richard Burts Thu, 09/06/2007 - 06:01


Yes indeed running EIGRP over both links and manipulating the metric to make the serial link the preferred route would be a very good way to achieve automatic failover. This is actually the solution that I would prefer. The phrasing of your original post led me to think in terms of solutions using static routes. Perhaps I should have thought about alternative solutions in my earlier response. But thinking about it now I would believe that running a dynamic routing protocol like EIGRP is the optimum solution.




This Discussion