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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 0.0.0.0 {
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!

Thanks,

spencer

 

1 REPLY 1
Routing

Re: Running OSPF on Redundant links

[ Edited ]
‎07-22-2010 08:24 AM

Hi,

 

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.

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