Routing multiple paths

Unanswered Question
Apr 7th, 2008

I am trying to figure out how to leverage two high speed circuits we have.

One of the circuits is 100Mb and the other is 45Mb. We use OSPF for our routing protocol. If you reference the attached file, I am trying to get the /24 address to go accross the 100Mb link to the /24 address. Then I need the /24 address to cross the 45 Mb link to the /24 address.

The idea behind splitting the traffic is that we want to send our less latency sensitive traffic on the 45Mb link and our more important production data on our 100Mb link. In the event that either link fails, we would want all the traffic to traverse the other link.

Thanks for any ideas!

I have this problem too.
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mpickens Mon, 04/07/2008 - 14:22

I had originally looked at PBR with the thought to doing Source-Based routing. Since my two WAN routers are not directly connected, in this situation there is a chance of redundancy failure. One WAN router cannot track the availability of the WAN side interface of the other WAN router. It would then continue to route packets back towards the failed circuit in this scenario based on what I saw.

The other idea I had was to try and modify the routing protocol metrics, but I could not seem to accomplish that. It appeared after testing that the metric was not modified at all after passing through the route-map. If someone has more insight into how to modify the routing metrics at different points along the path, I would love to hear about it.

Any other ideas? Or did I miss something in the PBR section that you had ment for me to notice?


Collin Clark Tue, 04/08/2008 - 05:28

You could use a route map with PBR, that should allow you to PBR and still have failover.

evsrajatgupta Tue, 04/08/2008 - 11:38

Hi mpickens,

(please rate)

Best solution will be Source-Based routing. You can also do Qos but is bit complex depending on the type of services you are running.

For Failover you can go for

Gateway Load Balancing Protocol


The Hot Standby Router Protocol (HSRP)

Just advice: In ospf load balance happens only on equal cost path, thus you 100 MB link will be used only up to 45 MB. When you have un-equal bandwidths use EIGRP if possible

mibrahim81 Thu, 04/10/2008 - 13:28

Dear mpickens ,

You should run two OSPF process , one

to get the /24 address to go accross the 100Mb link to the /24 address,and other to get the 24 address to go cross the 45 Mb link to the /24 address.

Also you can configure static routes with AD > 110 (OSPF AD) with next hop the other router for backup purposes .

when any link become down OSPF will withdraw the routes from the rouring table and the traffic will be forwarded to the other router ( link) according to the static route.

Mohamed Ibarhim



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