learn by doing

Debug Cisco laggy 3G Modem

I am writing this post as I’ve been having these strange issues with my backup 3G Internet link. My primary data provider was down for approximately 2 days so as I presented in this tutorial my router automatically failovers to the backup 3G data. The dynamic failover got in place just fine but after a couple of minutes of using the link it suddenly got stuck.

I checked the interface, it was up/up but pings just won’t come back - actually I think they didn’t even get to leave my router. After a shut/no shut of the interface everything looked back to normal and packets were passing just fine. I investigated further this issue but nothing indicated to a problem, the link was establish and the radio signal was strong.

One solution Adrian came with in hist post is to track the interface and based on its state to action an EEM script. I adapted a little his script to my needs and here’s what I decided to do: I will use the same ip sla to monitor by icmp a core router of my backup data link provider. If within 30 seconds no replies are received then the ip sla goes down and a script which resets the 3G modem is triggered.

One more thing I need to add is a static route to the IP address that I am monitoring in the IP SLA to go through the 3G interface and write the script lines - they are pretty straight forward.

Notice that the “test cellular” command is enabled after entering the “service internal” command from the config mode

ip sla 2
 icmp-echo source-interface Dialer2
 timeout 10000
 frequency 10
ip sla schedule 2 life forever start-time now
track 2 ip sla 2 reachability
event manager applet RESET-3G
 event track 2 state down<br />
 action 1.0 cli command "enable"
 action 2.0 cli command "test cellular 0 modem-power-cycle"