Setting up redundant links (network diagram included)

[krybabie]

Hi everyone

I have included a network diagram for reference purposes.

I need to connect this network as follows.

Router A:

Main router to upstream provider.

Ether Subinterfaced for wireless and PIX (upstream provider.)

This side working OK

RouterB and RouterC

My datacentre.

Router B Serial connection to routerA

RouterB serial connection to Router C

RouterC Ether connection via wireless to routerA

I need to setup the following:

route AC need to be primary route for data flow

route AB needs to be secondary route.

AC:AB needs to be 80:20 load balanced.

The links from RouterB and RouterC onto my network need to be setup redundantly.

They need to have the same IP so if one goes down the other is still up etc.

Hope you can help me with this problem

Thanks

Malcolm

[Kevin Dorrell]

Malcolm,

I've just seen your network diagram, and now I understand your architecture better. I wasn't previously aware of the 4 Mbps link from C to B. This really is a case for EIGRP between the three routers. EIGRP would give you almost exactly what you want. EIGRP would know that the path A-C-B has a bandwidth of 4 Mbps, and that A-C has 1 Mbps, and would share the traffic almost exactly 80:20.

I would start with a variance parameter of about 10. The 1 Mbps path is shorter, so the metric ratio may be slightly more than 4. Look at the ratio of the metrics; I guess it will work out somewhere in the range 3 to 5. The flows will be shared in the ratio of the metrics. You could tell it about the delay on the 54 Mbps path to adjust the ratio slightly.

The router links should all have different IP addresses, not the same. Link redundancy would be automatic.

More than that: the load would be shared 80:20 for traffic between A and C, but if you any hosts on the B router, most of their traffic would go A-B, which is what you would want.

Kevin Dorrell

Luxembourg

[krybabie]

hi

sorry some more i forgot.

RouterB and RouterA are connected via Serial and also via ether - they plug into the same switch on the same network.

What i want is for if one of the links plugging our router into the switch goes down the other will take control.

How can this be acheived if they have different IP's ?

Malcolm

[Kevin Dorrell]

IPs on the links are only used as "via". So for any particular destination you can have, say, two routes in the active routing table, one via IP1, and one via IP2. If these have been set up by EIGRP, then they can even have different metrics, and the flows will be shared in proportion to the metrics.

There is one additional complication brought on by having all these Ethernet links: that of detecting when a link goes down. If the two sides of the link are plugged into different switch ports (or worse, different switches), it may not be immediately obvious when the link becomes unusable. For example, if they are on different switches, and the link between the switches goes down, then the routers could take some time to cotton onto what has happened. But having said that, I should add that this is not the fault of EIGRP: it would be just as much of a problem with static routes ... no, more so - for static routes it would be a show-stopper.

(P;S. If you find any of this stuff useful, please don't forget to "rate this post". Thanks.)

Kevin Dorrell

Luxembourg