Failover to serial0 from tunnel0

[scoove]

Hi - Have been beating my head on this one for a few days. I have a "two cans and two strings" connection between two Cisco 4000s. The primary connection is a multi-hop Ethernet connection that goes through an ISP to a router at their location. 10 mbps fast connection. The backup is a point-to-point T1 from my 4000 to the 4000 at the ISP.

I built a GRE tunnel (tunnel0) between the two and have it working. I've got static routing set to default route to tunnel0's upstream as the primary, and serial0's upstream as the secondary (with a 200 weight). However, when I shutdown my ethernet that tunnel0 is based on, or shut down any device inbetween, tunnel0 still thinks it is up and subsequently doesn't send stuff to the secondary path. Also, the ISP 4000 has a /29 and a /28 subnet it is sending to my 4000.

Its been suggested that I use OSPF to do this, but the CCNP book's OSPF explanations are much more complicated than what I'm trying to do. I could post a config if it'd be appropriate. Any thoughts - perhaps I'm missing something on tunnel0 to sense it being down? Here's the critical part of my configuration (addresses changed):

!
interface Tunnel0
description Internet Primary over Ethernet to Microwv Link
ip address 10.37.236.230 255.255.255.252
no ip directed-broadcast
tunnel source Ethernet1
tunnel destination 10.37.236.134
tunnel key 123456
!
interface Ethernet0
description to our office DMZ
ip address 10.63.110.161 255.255.255.248 secondary
ip address 10.37.236.241 255.255.255.240
no ip directed-broadcast
no ip mroute-cache
media-type 10BaseT
no cdp enable
!
interface Ethernet1
description to the ISP's 6GHz radio and routers
ip address 172.31.2.4 255.255.255.248 secondary
ip address 10.37.236.237 255.255.255.252
no ip directed-broadcast
no ip mroute-cache
media-type 10BaseT
!
interface Serial0
description P2P T1 to our 4000 at ISP office
ip address 10.37.236.226 255.255.255.252
no ip directed-broadcast
no ip mroute-cache
!
interface Serial1
no ip address
no ip directed-broadcast
no ip mroute-cache
shutdown
no cdp enable
!
ip classless
ip route 0.0.0.0 0.0.0.0 10.37.236.229
ip route 0.0.0.0 0.0.0.0 10.37.236.225 200
!

Thanks for any thoughts!

*scoove*

 

[scoove]

Thought I'd add an update for those looking into the tunnel "always up" issue, there appears to be an option as of 12.2(8)T for enabling a keepalive parameter on a tunnel, due to the issue I observed of the tunnel staying alive even if actually down.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/grekpliv.htm

Unfortunately, while Cisco says the feature was incorporated in 12.0(23)S, my 12.0(28a) doesn't have support for it. Need to find an alternate approach. I wanted to post this info as it would definitely be a good path if my 4000 could support this load, or I was using another more modern Cisco.

*scoove*

 

[scoove]

Guess I'm stumped. Cisco claims GRE keepalive and the entire telco feature set is in IOS 12.2 Enterprise Plus, but it isn't there on the 4500/4700s.