[c-nsp] router-switch redundancy

[Stephen J. Wilcox]

On Sat, 13 Aug 2005, Paul Stewart wrote:

> > What I don't get about this is the two connections from each router
> into the same switch fabric. 
> 
> This can serve a couple of different purposes....load balancing and
> fault tolerance.... We use this above diagram for those two purposes in
> our system using OSPF. 

indeed, there must exist multiple vlans

> > In a simple world where you have a /24 with a bunch of servers plugged
> into the switches, how do you have two ports on one router in the same
> broadcast domain?
> 
> Then the above doesn't help a great deal.  Where it helps (in our case)
> is with clustered systems where you can run one portion of the cluster
> off switch A and the other portion off cluster B.  Therefore is you lose
> an entire switch you can still continue serving.  In our case the /24
> runs across both switches making this possible.

like he said :)

i've used exactly this setup for a large scale telco/isp deployment, we had two 
active-standby setups so that under normal operation load was balanced and under 
a failover half of it shifted.

Steve