Secondary Link/Link Based Routing

[KCIT21620]

Primary route takes IP traffic via fiber links from Router A to Router B and finally to Router C. There is also a Wireless Radio link between Router A and Router C and is configured as the backup route if the primary path goes down. If the fiber link between Router A and Router B goes down my backup route works perfectly. But here is my problem if the fiber link between Router B and C goes down I end up with a routing loop between Router A and Router B because Router A sees that the first fiber link as still working/being good. Is there a “link” based command/rule that I can configure that would ping through the primary link and then if say the primary link went down for more than 15 sec switch over to the secondary link? And then if the primary link comes back up switch back automatically? I am open to any suggestions it doesn’t necessarily have to be link based; it is just the first thing I thought of.

[amsodhi · Accepted solution]

You could configure IP SLA on router A to fix this issue:-

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/44sg/configuration/guide/Wrapper-44SG/swipsla.html

ip sla 1
 icmp-echo 4.2.2.2 source-interface FastEthernet8
 timeout 2000
 threshold 2000
 frequency 30
ip sla schedule 1 life forever start-time now
track 1 ip sla 1 reachability
delay up 3 down 3

[KCIT21620]

I tired the commands you posted with no success. Maybe I’m not using them correctly? I put in the IP address of router C instead of 4.2.2.2 and put in the interface of the fiber link instead of FastEhternet8, which was the correct thing to do???

Also from the link you posted about the SLA commands it appears SLA is a “monitoring/measuring” tool, so is SLA the correct command to be used in this scenario to allow a backup link to work?

[KCIT21620]

After some more testing and working with the above noted commands I was able to get them working. I found that you have to add a "Track 1" to the end of the IP route in question to enable the rule.

Thanks for your help!

[Joseph W. Doherty]

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Using a dynamic routing protocol isn't possible?