US patent 5473599

sthaug at sthaug at
Wed May 7 04:14:01 UTC 2014

> So, then the only problem, perhaps, is that noone has apparently
> bothered to explicitly document that both VRRP and CARP use
> 00:00:5e:00:01:xx MAC addresses, and that the "xx" part comes from the
> "Virtual Router IDentifier (VRID)" in VRRP and "virtual host ID
> (VHID)" in CARP, providing a colliding namespace, so, one cannot run
> both with the same Virtual ID on the same network segment.

RFC 2338, from April 1998:

7.3 Virtual Router MAC Address

   The virtual router MAC address associated with a virtual router is an
   IEEE 802 MAC Address in the following format:

      00-00-5E-00-01-{VRID} (in hex in internet standard bit-order)

   The first three octets are derived from the IANA's OUI.  The next two
   octets (00-01) indicate the address block assigned to the VRRP
   protocol.  {VRID} is the VRRP Virtual Router Identifier.  This
   mapping provides for up to 255 VRRP routers on a network.

Also repeated in RFC 3768 (April 2004) and RFC 5798 (March 2010).

Steinar Haug, Nethelp consulting, sthaug at

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