OSPF route poisoning ? 1

[sb2323]

Hi

The scenario
I have got two 3640's that are connected to a mainframe and is runing ospf. The two routers are running hsrp but the mainframe is targeting the standby router. The mainframe is learnig the route to the standby route via ospf.

How I can I poison the route that is pointing towards the stanby router ?

Cheers

 

[ADB100]

The only way you could do this would be to make the router (HSRP Standby) advertise a higher (worse) metric than the other router (HSRP Active). If these are OSPF Internal routes then it may be a bit tricky; you need to have a look in the OSPF database and determine where the routes are coming from and then somehow influence the metric so it appears better on one router than the other.

Personally I would disable OSPF on the mainframe (or on the particular interface) and rely on HSRP for redundancy. All in line with the KISS approach ;o)

Andy

 

[sb2323]

Andy

Thanks for the info, Forgive me for asking a stupid question. Which command do have use to advertise a higher metric on the standby router ?. I have tried to get the mainframe boys to use static routing, but they are having none of it.

Cheers

 

[ADB100]

If they are Internal or learned External routes then you can't thats why I said it would be tricky - OSPF is a link-state protocol so all routers must have consistent databases - you can't just add a route-map and say on one router make its Metric 100 and on the other 110.
If its an external route and it is being redistributed by these 2 routers then it should be easy you can make the metric different through route-maps or redistribution statements.
Can you post the routing table on the 2 routers for the particular route you are looking at, also if its possible post the OSPF configuration from each router.

andy

 

[sb2323]

Hi

Another question , Is there anyway of advertising an HSRP address for the two mainframes to use ?

 

[ADB100]

No - HSRP is a default-gateway redundancy protocol; the active HSRP Router owns the 'Phantom' HSRP IP and MAC address, if it fails or its priority is degraded then the Standby HSRP Router takes over these Phantom addresses. This is designed for networks where the Workstations only have a default gateway configured and have no other way of getting IP packets off the local Network/Subnet.
You are also running OSPF where each OSPF-speaking device on the the Broadcast Medium (I assume Ethernet?) forms adjacencies with all OSPF speakers (a DR and a BDR also get elected etc). The problem is your Mainframe is participating in OSPF and therefore knows the topology of your network (or the particular OSPF area it is in depending on your OSPF configuration), and therefore makes its own mind up as to the best path to a destination.

I hope this helps or at least points you in a better direction?

Andy

 

[sb2323]

Andy

Thanks for the info, One of our tier3 guys has recommended using the default-information originate metric 110 for router and default-information originate metric 100 for the other router. I was under the impression that this command would only inject a default route of 0.0.0.0 into that ospf area and thus be the last route chosen. Are my assumptions correct ?

 

[baddos]

As always a more specific route will be preferred over a default route.

 

[ADB100]

It depends on the area type and how the routes are being learned. Can you show us the routing table on the 2 routers and maybe I can shed some more light on this?

Andy