Configure 3G as backup link

[Patrick McHenry]

Hi,

I've got a 881 working with a 3G Card. Even the Cisco 7965 phone is working well off it. Can anyone provide me with a good doc for configuring the 3G interface as a backup link to Comcast?

Thanks, Pat.   

[smitesh kharecha]

Hi Pat,

Easiest way to do is to mark that interface as a backup interface.

Below is the sample config.

let assume your Comcast link is present on fa0/1 and your 3G is on Ce0 interface.

then, all you have to do is:

interface fa0/1

backup interface Ce0

Regards,

Smitesh

PS: Please rate helpful posts...

[Patrick McHenry]

Will this allow interface fa0 to reclaim it's role as the outgoing interface if it happens to come back up.

The thing is, is that the outgoing interface might remain up but, the Internet connection might be down. So, I believe there is much more involved in making a back up 3G interface. For instance, shouldn't I be using an SLA to continuously monitor the connection to the headend router( I didn't mention that this would be a DMVPN) so, if the headend is not reachable anymore via the fa0 interface then, the 3G will kick take over.

Thanks, Pat.

[pgasparovic]

Hi there,

though after 1,5 years, FYI to you and others looking for some startup with 3G/4G deployment in Cisco IOS :

http://www.cisco.com/c/dam/en/us/td/docs/solutions/CVD/Dec2013/CVD-VPNRemoteSiteOver3G4GDesignGuide-DEC13.pdf

Anyway, backup is rather old command and performs reliable job (with fixed interfaces for me so far). I have just come across bug-like behaviour yesterday, searching here now for some tips before even contacting TAC, when 3G does not probably attach (have not studied detailed stuff) to the network upon primary link failure, even though there is active LAN traffic pushed into the WAN. I started off with backup cmd yesterday, possibly today to play with EEM to see if explicit shut/unshut of Cellular interface works 100% - if it does not work, then I turn to TAC. Any prompt hints from 3G skilled people are welcome, thanks.

Peter