Running OSPF on Redundant links

‎07-22-2010 07:48 AM

I have 2 xEX4200 switches (VC'd together) connecting to a single Cisco 3800 MPLS router.


I am running 1 link from each switch to the 2 interfaces on the Cisco router and am running OSPF on both sides. Each link will have its own /30 IP subnet and be in its own VLAN.


I am doing this in case we lose one switch, so that the other switch will still have connectivity to the MPLS cloud.


I wanted to assign a higher metric to one of the links in OSPF on the EX4200 switches to have OSPF prefer one of the other, something like this:


protocols {
ospf {
area {
interface ge-0/0/0.0 {
metric 10;
interface ge-0/0/1.0 {
metric 20;



Can someone confirm (or deny) if this will work? Any help would be greatly appreciated!





Re: Running OSPF on Redundant links

[ Edited ]
‎07-22-2010 08:24 AM



it would be better to have a third switch in VC as RE (with no L3 uplink towards Cisco). Then your setup would work like a charm (after you enable graceful-restart for OSPF). What happens if RE fails in your current topology:

     - RE failure would also cause OSPF topology change as L3 link towards Cisco would go down

     - this would interrupt graceful-restart

     - traffic blackhole until OSPF is restarted


Btw. This restriction would go away once Non-Stop Routing is implemented for OSPF (roadmap item).


Kind Regards

Michael Pergament


If this worked for you please flag my post as an "Accepted Solution" so others can benefit. A kudo would be cool if you think I earned it.