Reliable Backup Static Routing using Object Tracking
Posted on 2010-09-10
I've been tasked with making a proper failover on the a router running Cisco IOS 12.4
The connectivity consists of a T1 (serial) primary connection, and another firewall hosting a VPN over an internet connection for the backup connection.
I've built it out, and it all works great... except....
This T1 is a little schitzophrenic. Every now and then it drops a packet or two (like 3 times a minute.) This has no effect whatsoever on our primary use of this connection, which is telnet traffic for an AS/400.
The problem is, the tracked SLA changes from up to down and back three times a minute. Meaning it changes the routing three times a minute. This kind of behaviour is VERY disruptive to the AS/400 traffic.
Here's my wish - I want the SLA to ONLY switch state if it loses say 10 consecutive pings. I thought the answer was the "threshold" quantity on the SLA, but it not only seems to have no effect (state still changing) but much of my reading says it's connected to a "hysterisis" function - which I don't really understand. Even if I crank the "threshold" up to ridiculous quantities (30000 say) it still logs the tracked object as changing state just as frequently.
The "frequency" is just how often the SLA pings. I've increased this quantity too, but really it's like Russian roulette as to whether it gets a good ping or a bad ping when it goes off.
Can anyone tell me what I'm missing here?