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PIX 506 and Cisco cable modem with OSPF

The network is setup as described below:

Site 1:

DSL Modem

PIX 506 (Handles PPPoE Authentication)

Cisco 2620 with T1 to site 2


Cisco Cable Modem

PIX 506 (Gets DHCP address through cable modem)

Cisco 2620 with T1 to site 1

I have the network setup route internet traffic via the connection closest to the local site unless the local sites internet connection is down. It that case traffic is routed out the end that still maintains a connection. I set this up using OSPF on the PIXs and the routers. The problem is that when the cable or DSL connection goes down, the PIXs do not recognize that the route is down until you physically pull the ethernet cable or shutdown the outside interface. The cable company doesn't allow OSPF on their modems so I am looking for another solution. Thanks in advance.


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Re: PIX 506 and Cisco cable modem with OSPF

Hi Matt,

I had a similar situation where I wanted to monitor the primary link and if it went down, wanted to route the traffic over a secondary link. However, since the ethernet cable remains plugged in to the modem, even though the route goes down, the router thinks the link is still up. What I used to get around this is Reliable Static Routing Backup using Object Tracking. Essentially it pings across the primary link and if it doesn't receive enough responses (determined by the threshold that you set) then it will determine that the link is down and failover to the secondary link, which is your next static route in the routing table. If the primary link comes back up it will start using it again. This way you don't have to unplug the ethernet cable between your router and modem if the link goes down, and you don't have to plug it back in when the link comes back up. It does it automatically for you whether a response is received from the ping or not. If you can setup static routing in place of OSPF and your IOS accepts the ip sla monitor commands then this should work.

HTH. -Joe

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