US patent 5473599

Nick Hilliard nick at
Thu May 8 11:00:00 UTC 2014

On 08/05/2014 11:25, Henning Brauer wrote:
> you shouldn't see issues but log spam.

maybe you misunderstand the problem.  If you have vrrp and carp on the same
vlan, using the same vrrp group ID as VHID, then each virtual IP will arp
for the same mac address on that vlan.

This messes up the switch's forwarding table for that particular vlan
because it sees multiple entries from different ports for the same mac
address.  Switches will not do unicast replication in this situation, but
instead will forward all traffic for a particular destination mac address
to the port which announced the mac address most recently.

In other words, this is much more serious than log spam: it is guaranteed
to cause network downtime, because you cannot have two hosts on the same L2
domain using the same mac address, but doing different things.


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