Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

ospf equal cost

I´ve two E1 links, between 2 equal routers.

These routers have 2 FastEthernets ports.

How can I do for ethernet traffic E0 , goes by Serial link S0, and ethernet traffic E1, goes by Serial link S1 ?

Only e0 y e1, goes traffic by s0 y s1 , if s0 goes down or s1 goes down....

note: please, i need to implementing this over OSPF.

New Member

Re: ospf equal cost

Why do you want to separate the traffic physically? You can use OSPF load balance to aggregate bandwidth and you can use a QoS feature (like custom-queue) to guarantee 50% for each type of traffic. In this case, if one type of traffic is not present, the other will use two E1 links.

Re: ospf equal cost

But , I dosen´t wants use two E1 lines.

I need use each link separatly , but if any link goes down, i need use the other link.

Is thsi possible with ABR concept? What are you think?

New Member

Re: ospf equal cost

I’m not sure about which you want. I've understand that you have two routers and four LAN and two E1 circuits between the routers. Like this:

LAN1 --!Router!----E1--------!Router!--LAN3

LAN2 --!....A......!----E1--------!....B.....!--LAN4

I’ve understand that you want that the traffic between LAN1 and LAN3 uses an E1 circuit and the traffic between LAN2 and LAN4 it uses the other circuit. If "circuit down" then both traffic use the active circuit.

In this case, only the OSPF should not be the best option to isolate the traffic. If you use two autonomous systems maybe you get to isolate the traffic with OSPF, but I don't recommend.

You can use PBR (Policy-based Routing) to define for which interface the traffic should be routed. For example:

access-list 101 permit

access-list 102 permit

route-map circ1 permit 10

match ip address 101

set next-interface serial0

route-map circ2 permit 10

match ip address 102

set next-interface serial1

I never tried this before and I’m not right about what it happens when a serial goes down, but I think this is a good clue.

Other way to define the path for different types of traffic is MPLS-TE, but this is not possible in all router models.

I already used a similar structure with OSPF:

LAN1 --!Router!----E1--------!Router!--LAN3

LAN2 --!....A......!----E1-\.../---!....B......!--LAN4


LAN1 --!Router!----E1-/...\----!Router!--LAN3

LAN2 --!....C......!----E1--------!....D.....!--LAN4

It is a high availability solution, if the circuits are provided by different ISP. But I haven’t been needing to separate the traffic in circuits. I’ve been needing to guarantee 40% of the band for a certain type of traffic, 20% for another and 40% for the others. I’ve applied custom-queue.

Summarizing: there are some ways of implementing a solution for the problem that you propose, but I think only the OSPF won't be a satisfactory solution.

I hope that I’ve helped you.

CreatePlease to create content