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New Member

OSPF load balancing check

Load balancing for serial link for OSPF has been configured using backup load. Backup line is a PRI line calling another PRI line. both pri are configured for loopback address. so in output of show ip ospf nei command it shows neighbor relationship formed with the same address ( loop back address ) from that dialer. This seems ok But on this link no traffic seems to flow, it still flows from the main serial link. It was checked by using show interface dialer and corresponding channel from PRI group.

Is there any way to check or to make traffic use this backup link.

Thanks in advance

Subodh

7 REPLIES
New Member

Re: OSPF load balancing check

OSPF will only load balance across equal-cost paths. Check that the cost of routes coming in from the backup PRI is equal to the cost of routes coming from the main link.

Also check you're actually seeing LSA's as expected over the second line.

New Member

Re: OSPF load balancing check

Quick way : check that you can see both routes in ur routing table ( two equal path via OSPF)..

Hall of Fame Super Silver

Re: OSPF load balancing check

Bapat

When you say that load sharing has been configured using backup load am I correct in assuming that the primary serial interface specifies the backup-interface command pointing to the PRI (or to a dialer interface on the PRI)? It would help us to understand what is going on and to find an answer if you would post the router config.

If the primary serial does specify backup-interface then the backup interface will be down with no OSPF hello messages exchanged and no routes learned on the backup interface unless the primary interface is down or the load threshold is exceeded. So most of the time there will not be two OSPF routes to the destination.

What is the load threshold set to? And when you were testing did you make sure that there was enough traffic over the primary interface to exceed the load threshold?

HTH

Rick

New Member

Re: OSPF load balancing check

If I give command

#sh ip route a.b.c.d

To the destination where we have configured OSPF load balancing, will it show two separate paths one from original serial line and one more from PRI-PRI line , great I will check it out and will get back.

Thanks a Lot !

Subodh

Hall of Fame Super Silver

Re: OSPF load balancing check

Subodh

Whether you will see two separate paths depends on how the router is configured and especially depends on whether the second link is active and has established an OSPF neighbor relationship.

As I suggested before it would be helpful if you would post the router config so that we could understand how the interfaces were set up. It would also be helpful if you would post the output of show ip ospf neighbor and the output from show ip route.

HTH

Rick

New Member

Re: OSPF load balancing check

Hi,

It worked !!

I saw the cost of the interfaces, one for serial line and another for PRI channel. It was exact at one location but it was different at another location. I thaught that both channels are of same bandwidth 64 kbps both will have the same ospf cost. but PRI interface cost was greater that serial link cost. so I mannually gave cost to that dialer interface and it worked.

I gave command sh ip route A.B.C.D

it is was showing two paths one with serial link and anothe with dialer.

There was sufficient traffic to trigger the dialer interface i.e PRI.

Thanks a Lot friends.

Next my objective is to configure one PRI channel as aback up to serial line if it totally fails and make OSPF run on that. I plan to use Dialer watch hope it would work without any problem. I will post another query if i had any problems.

Thanks again!!

Subodh

Re: OSPF load balancing check

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