networking: Cisco 3640 and a GPRS router

[Edgar Zapata]

I have a Cisco 3640 router.
What I want is to set up the router so in case the Ethernet link fails, network users will still be able to connect to the Interent via a GPRS router.
Is there a way to set that up on a Cisco 3640?
The regular use is this router will send traffic over to another router Cisco 837(this one has an Internet connection) within the same network in a different building.
I mean, if the Ethernet link fails (if it is cut intendedly) is there a way to have the 3640 router send all traffic to a GPRS router within the same room/same network?
These are the interfaces the router has:
1 ethernet
1 serial (I don't intend to use this one at all)
1 bri

I need this because the room (it's actually a bunker) where the 3640 and the GPRS routers are located are attacks susceptible.

thank you much.
regards.

[Ron Kinner · Accepted solution]

Appears that the 837 can do IGRP or RIP if you have the PLUS version of the code. If you put a default route on the 837 and let it talk to the 3640 using IGRP or RIP, the 3640 should pick up the default route to the internet and use it. Then you add a static route

ip route 0.0.0.0 0.0.0.0 IPofGPRSrtr 200

to the 3640. Since it has a high metric it will be ignored until communication with the 837 stops and IGRP/RIP drops the default route. Since it is now the only way to get there the route to the GPRS router will now be used.

Ron

[Terhorst]

Hi Edgar,

Would be a nice post for the Cisco forum I assume.

Regards,
Alexander

[Edgar Zapata]

Ron, thank you much.
I followed your directions.
the 3640's routes stand as follow:

C 192.168.91.0/24 is directly connected, Ethernet0/0
S 192.168.99.0/24 is directly connected, Ethernet0/0
S* 0.0.0.0/0 [200/0] via 192.168.99.74

not sure if this is right.

Th..., I already posted this in the Cisco forum.

regards.

[Ron Kinner]

You will also need to turn on IGRP (or does it do EIGRP?)

Router igrp 1
network 192.168.91.0

Also the next hop should always be on the same subnet as connected so I don't really like your default route.

*** edited to comply with forum guidelines ***
Ron