Load sharing and Redundancy - Scenario

Answered Question
Jun 11th, 2009


I have three links on a new site with unequal bandwidth, is it possible to combine all to have load sharing and redundancy

Link#1 Point-to-Point = 4MB ( Ethernet )

Link#2 Point-to-Point = 2MB ( Fiber )

Link#3 Point-to-Point = 6MB ( Ethernet )

Can someone share steps how to achieve it.


I have this problem too.
0 votes
Correct Answer by Joseph W. Doherty about 7 years 4 months ago

If you're only unfamilar with EIGRP configuration for unequal costing, this might help: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

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Overall Rating: 4 (1 ratings)
paul.matthews Thu, 06/11/2009 - 01:55

The best routing protocol for that would probably be EIGRP. That allows load balancing over unequal cost links, you just need to make sure variance is set - I wuld start with variance set to 4.

Joseph W. Doherty Thu, 06/11/2009 - 05:30

As Paul suggests, EIGRP can direct number of flows to each link based on its bandwidth. However, unless all flows use equal bandwidth, don't be surprised to see actual link loading not balanced.

If EIGRP isn't an option, for routing protocols that support equal costed multiple paths, e.g. OSPF, you might "lie" to the protocol to have it use all 3 of your paths. (Since your bandwidths aren't "too" far apart, this could be an option for you.)

Lastly, Cisco routers, in their later IOS versions, support a new technolgy, OER/PfR. This technology can dynamically load balance, but there are many restrictions to using it.

In theory, pehaps the best combination would be EIGRP to initially direct flows per link bandwidth and OER/PfR to issure actual load is balanced.

ronald.ramzy Thu, 06/11/2009 - 09:47


Thanks for your input.

I have attached the network diagram, can you help with steps to configure Eigrp to load balance the link.

Can you help me to understand if I can use EtherChannel for this scenario

Joseph W. Doherty Thu, 06/11/2009 - 10:44

Your diagram shows OSPF already being used? Although it's possible to use EIGRP across the links, if you're already using OSPF across them, you might just set each link's OSPF cost the same and see how that works for you.

Concerning Etherchannel, I think(?) like interfaces are required.

ronald.ramzy Fri, 06/12/2009 - 08:33

can you give me steps to configure EIGRP.

Will EtherChannel help in my scenario.

Paolo Bevilacqua Fri, 06/12/2009 - 08:47

Do you want to do yourself a BIG favor?

Ask your SP to consolidate all links in one, and get a good SLA for it.

You will need a lot of aspirine otherwise.

Paolo Bevilacqua Fri, 06/12/2009 - 12:24

Don't forget to update us on how EIGRP unequal sharing works for you -- especially when offered traffic is near to the sum on BW.


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