[nsp] HSRP protocol extensions?

[Ed Ravin]

It looks like somewhere in IOS 12.x Cisco added a new opcode
(value 3) to HSRP.  It's not in the RFC, and neither of the packet
decoders (Ethereal, tcpdump) that I've tried know about it.
In fact, older versions of IOS would report it as a "malformed
packet", though HSRP still seemed to work properly.

Anybody know what this does, or where it is documented?

	-- Ed