Blue Coat ProxySG VIP and Cisco switches need Multicast enabled

You have a pair of shiny new ProxySG boxen that you want to setup in active / standby for high availability. You configure it up and everything seems to work, and then it doesn’t, or other equipment on the same network experiences random problems.

What you are having is a Multicast problem with your Ethernet switches, most likely your Cisco switches, that has the problem. How to understand and solve the problem after the jump.