Multiple Internet connections

[ld2000]

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.

[vcjones]

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 track xyz

ip route 128.0.0.0 128.0.0.0 track xyz

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

www.networkingunlimited.com

[ld2000]

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...

[vcjones]

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

www.networkingunlimited.com