[c-nsp] router-switch redundancy

[Mark Kent]

In more than a few places on the cisco web site they have
diagrams like this:

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

designed so that either router can fail and things still work
for the servers connected to the switches.

What I don't get about this is the two connections
from each router into the same switch fabric.  

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?

Thanks,
-mark