Ospf load balancing

Unanswered Question
May 22nd, 2012

hello expert,

  I want the load balancing on ospf network that

1. subnet 1.1.1.0/24 reach at destination through  int fa0/0 (Router R4)

2. Subnet 11.11.11.0/24 reach at destination through int fa0/1 (Router R4).

I am not using any ospf cost or bandwidth .

how i can do it ?

thanks

mukesh

I have this problem too.
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sheahankp Tue, 05/22/2012 - 08:27

OSPF only performs equal-cost load-balancing. So manually set the cost to the same on both links if they are different. Also, under the ospf process, you will need to enter maximum-paths 2.

Kind Regards,

Kevin

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Giuseppe Larosa Tue, 05/22/2012 - 08:59

Hello Mukesh,

load balancing works based on IP flows that are defined on IP source IP destination.

With OSPF you can perform by default load balancing over up to 4 equal cost different paths ( Equal Cost Multi Path ECMP).

Choicing the exit interface based on the source address as you would like to do is not possible with a dynamic routing protocol that is destination based.

You should use PBR (policy based routing) to choice the exit interface based on source address.

PBR allows for a setup like that but it processes traffic that is received on a router interface.

see

http://www.cisco.com/en/US/docs/ios/12_0/qos/configuration/guide/qcpolicy.html

Hope to help

Giuseppe

JosephDoherty Tue, 05/22/2012 - 16:47

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Posting

Giuseppe Larosa wrote:

With OSPF you can perform by default load balancing over up to 4 equal cost different paths ( Equal Cost Multi Path ECMP).

If I remember correctly, most Cisco OSPF devices default to 4 equal cost paths but that might be increased with maximum-paths command.  Older IOSs, if I also remember correctly, supported up to 6 equal cost paths, and I think, more recent IOSs support many more (16? 32?).

mukeshrulaniya Tue, 05/22/2012 - 23:15

Hello Giuseppe,

Yes, i can do it through the PBR or static route but problem is that when one link goes down then i need to manually change the policy or static route that i am using now but i want dynamically solution so i have no outage time for any subnet.

thanks

Cadet Alain Tue, 05/22/2012 - 23:37

Hi,

You can use floating static routes with tracking for dynamic failover and you can also do tracking  in PBR.

Regards.

Alain.

Giuseppe Larosa Wed, 05/23/2012 - 04:54

Hello Mukesh,

follow Alain's suggestions tracking can be combined with PBR.

see

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtpbrtrk.html

for the opposite direction you can use static routes with tracking

see

http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html

in your case you can simply have a primary tracked static route and the backup can be provided by OSPF dynamically

Hope to help

Giuseppe

Giuseppe Larosa Wed, 05/23/2012 - 04:59

Hello Joseph,

you remember correctly.

the upper limit is platform dependent and OS type and version dependent.

According to command reference support for 16 paths have been added in 12.2(33)SXH that is an IOS version for C6500 with Sup720.

see

http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_pi/command/iri-cr-a1.html#GUID-C8B4E7F7-3DEE-4C57-BC7B-29D58B6DEFF3

Even higher number of parallel paths may be supported in IOS XR on CRS, 12000 and ASR 9000.

Hope to help

Giuseppe

sheahankp Tue, 05/22/2012 - 11:54

Yes, Giuseppe is on-point with his recommendations. I misunderstood your initial question. PBR is your best option.

Kind Regards,

Kevin

**Please remember to rate helpful posts as well as mark the question as 'answered' once your issue is resolved. This will help others to find your solution faster.

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