Archive for June, 2008

VRRP

June 23rd, 2008
We have two Draytek v3300 routers which connect the school LAN to 4 internet feeds, three ADSL lines and one 10M leased line to Brighton and Hove City Council.
The routers have a failover feature where by the use of VRRP, a single redundant IP is presented to the network and packets for that IP are sent to whichever of the Drayteks is in “Master” mode (ie the primary one, or the secondary in the absence of the primary).
This used to work, but has always been a bit flakey when it comes to rebooting either of the routers.
I recently upgraded the firmware on both routers and now cannot get both routers to come back up together.
My best guess is the new Procurve switches are failing one or more ports because at L2, they’re seeing the same MAC address presented by two ports as VRRP negotiates who gets the virtual MAC as “Master”.

These two intemate that this is a regular problem – certainly with Cisco switches, so I may just be right!

Ideas to test:

  • Disable STP on the ports connected to the Draytek routers
  • Change the VRRP ID they use from 1 to an obscure number in case something else on the network is attempting VRRP negotiation on group 1
  • Plug both Drayteks in to an intermediate hub (hub becomes SPOF)