Jeroen Ruigrok supplied these links about patent issues with Cisco’s VRRP during a thread about importing OpenBSD’s CARP as part of pf.

http://www.in-addr.de/pipermail/lvs-users/2001-November/004135.html
http://kerneltrap.org/node/view/477/1567
http://kerneltrap.org/comment/reply/477/1567
http://marc.theaimsgroup.com/?l=openbsd-misc&m=102883972229241&w=2
https://www1.ietf.org/mail-archive/working-groups/vrrp/current/msg00318.html