07-21-2004 10:13 AM - edited 03-02-2019 05:13 PM
We have a T-1 to our primary ISP at our main site through a PIX 516E. We have a couple of remote sites that are interconnected via frame relay, and use our main sites internet connection. We are setting up cable modems (UBR 900's) at our remote sites for a secondary internet connection in case the primary goes down. All sites have Cisco 1721's and we have EIGRP running between the routers. Basically I'm looking for the main sites router to let the remote routers know that the ISP link is down, and to use their UBR connections. I was reading about configuring SAA probes to an internet site. Would this be a way to go? Attached is a .gif of our situation. Thanks in advance.
07-21-2004 11:36 AM
Assuming each site uses the local 1721 for their default gateway...
Use SAA on the HQ router to detect loss of primary ISP path, but instead of tracking the default route, track a pair of longer prefix routes to override the default route advertised by the UBR routers as follows:
ip route 0.0.0.0 128.0.0.0
ip route 128.0.0.0 128.0.0.0
Since longer prefix trumps all other routing metrics, the path through the PIX 516 will be used by everyone if it is available.
Note that this will also allow the HQ to use the nearest remote's DSL for ISP access if the primary ISP goes down. To prevent that, add the line
ip route 0.0.0.0 0.0.0.0 null0
on the HQ router (only).
Good luck and have fun!
Vincent C Jones
07-22-2004 05:02 AM
Just a quick question. The UBR's are owned by the cable company, and are not advertising anything into the network. Does this change anything? Sorry for the novice questions...
07-22-2004 05:52 AM
It doesn't really change anything, as long as the only router which even knows about each UBR is the local 1721.
The other thing you will want to consider is if you are not using the UBR for anything except backup, you will need a mechanism in place to detect when they fail while not in use. Otherwise, you will find that there is a high probability that they won't be working when you need them.
Good luck and have fun!
Vincent C Jones
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