[c-nsp] Quick question on HSRP...

[Jeff Kell]

Quick question for someone that's been there, done that, as I'm a bit
rushed to try to lab test this...

We're adding some new routers (4500Xs) for an upgraded server farm
arrangement with a number of server-side vlans / VRFs.  The plan was to
trunk it with the existing L3 router, and fire up HSRP (v2) across them
to transition the L3 routing to the new router without being too
terribly disruptive.  Not sure if we want to leave the HSRP in place
(thinking yes) or remove it (and the old router) after the migration,
but will cross that bridge when we get there.

HSRP would place the current "default gateway" as the virtual IP, and I
presume it will pick up a new MAC address.  I'm concerned this will
affect the active hosts with the ARP cached for their gateway.  The MAC
address would still be valid (should match the original gateway) but the
traffic would be directed to the original (now virtual) IP, as opposed
to the new "physical" gateway on the router.

So just how "disruptive" will introducing HSRP really be?

Jeff