Load balancing on ethernet

Unanswered Question
Dec 21st, 2007

Dear all ,

Is there an option to configure Primary and Backup on two Ethernet links terminating on same

router at A-end and and different router at B-End


I have this problem too.
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royalblues Sat, 12/22/2007 - 00:04

Well you can definitely configure the routing in such a way that it loadbalances on the 2 links, it would never be effective.

The other end could be sending the traffic to only one router causing assymetric routing and might receive packet out of sequence



Richard Burts Sat, 12/22/2007 - 15:03


I seem to understand your post and your requirements differently from my colleagues. I understand that your requirement is to have a primary link and a backup link and not necessarily to have load balancing. They have interpreted the requirement to be load balancing. Perhaps you can clarify what your requirement is.

It would also help to know whether you want to do this with static routing or with a dynamic protocol.

I believe that you could accomplish primary and backup using static routes by configuring a static route to use the first Ethernet and configuring a floating static route to use the second Ethernet. There is an issue with static routes detecting link failure on Ethernet interfaces and you would want to use the feature of Reliable Static Routing using Object Tracking to work around this. This link gives information on this feature:


And if you want primary and backup with a dynamic routing protocol then you just adjust the metrics to make one link look better than the other link.



mahesh-gohil Sun, 12/23/2007 - 20:29

Ya rick,

Exactly I want primary and backup scenario.

The topology is attached in attachment

I have option to use static as well as BGP ..at anyway link should work in primary and backup

Pl. provide guidance in between I am going for link you have provided to me



Richard Burts Mon, 12/24/2007 - 10:35


Thanks for the information about the topology. It does raise a question about your objective. When you asked about configuring primary and backup that usually implies two links that both get to the same destination. (You want one link to get to the destination as the primary path, and you want the other link to get to that same destination as backup if the primary fails.) But the topology that you show would appear that the routers RA and RB would not get to the same destination.

If there is not some destination with 2 different ways to get to it, then what is the primary and backup doing?

Please clarify. If we understood what you are trying to accomplish we might be able to help figure out how to do it. But now I am quite confused.



mahesh-gohil Tue, 12/25/2007 - 20:17

Dear rick,

It is internet link that we provide to customer ..Now RA and RB both are part of our ISP Network. Ultimately it reaches to our internet gateway router via so many routers..Because our goal is to provide customer internet to CE router if one of that link fail..

Still u feel confused do let me know

Thanks for your help



waleed_amer Wed, 12/26/2007 - 02:58

Hi Mahesh,

i think u need to backup from CE Router side an ethernet main link which will be always up from CE Router side if u want to backup ethernet link between RA & SA(Switch) so u have to track (at CE Router) the ip or interface of RA ethernet.

u can use 2 default routes @ CE router with different AD (main default route with AD more than backup default route) without tracking it will use backup route because of AD is less than main route but with tracking RA ethernet interface will not install backup route @ routing table until the RA ethernet be down.

if it what u need we can discuss how it will be configured.



mahesh-gohil Wed, 12/26/2007 - 20:55


with any kind of solution no traffic should be dropped from CE Router if one of link to RA or RB fails. But please remember that it is ethernet link means if link between RA-SA goes down it show UP in CE Router ...so there must be something which enabled backup link not based on "Line protocol status" ..




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