[c-nsp] router-switch redundancy

[Paul Stewart]

           {Internet}
            /      \
           /        \
       [routerA]   [routerB]
        /   \       /    \
       /     \     /      \
      /       \   /        \
     /         \ /          \
    /           /            \
   /           / \            \
  /           /   \            \
 -------------    ---------------
 |           |    |             |
 |  switch   |----|   switch    |
 |           |    |             |
 -------------    ---------------

> 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. 

> 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.

Hope that helps.

Paul