can we load balance (perfectly) over unequal bandwidth links using cef..? In other words,whether cef is intelligent enough to switch packets based on the bandwidth criteria in a link..?
And also,can I attain the same objective using Multilink..?
cef
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I think you would get a better result using multilink. Multilink will take several links (I understand that it compensates for different capacity of the links if they are unequal) and spread data over all of the links.
With CEF you will get load balancing that depends on what is present in the routing table. If you use EIGRP as your routing protocol and have configured appropriate variance under EIGRP then you should get the unequal links in the routing table. But if you use a protocol like OSPF it will not choose unequal paths. If you want multiple paths you will need to force OSPF to believe that they are equal by adjusting the interface cost. And if you do that the router believes that the links are equal and so CEF has no way to compensate for different capacity.
Thanks for your reply.I got ur explanation on cef.But I think I didnt get ur explanation on Multilink.
By saying “(I understand that it compensates for different capacity of the links if they are unequal)”,u meant to say that if I have 2 links 64k and 2 mb bundled together using multilink,load sharing will happen in such a way that more data will pass thru the 2 MB (2 MB/64 K times the data flow on 64K link) than the 64K link..
Pls correct me if my understanding is wrong.
Thanks
If you have a 2MB link and a 128 KB link, MLPP will try to load-balance on both the link with the best effort it can. If your traffic is more than 256 KB, your 128 KB link will get saturated and your 2 MB link will passs the data normally. You cannot set MLPP to behave like if your 128 KB link is full, to pass more packet from the second link. To the best of my knowledge it will behave like this and I will have somebody commnet on this.
I have done multilink but not over unequal links, so I can not speak from experience. But my understanding of the documentation is that if you have a 2 mb link and a 64 k link that multilink will load each link proportionately. The lower speed link should not become saturated or over-driven.
To go back to the original question of load balancing on unequal links with cef or with multilink I think that multilink is a better solution. Multilink will have a better understanding of the capacity of the links and will use the links more effectively. CEF can only work with what is in the routing table. And what is in the routing table will depend on what routing protocol you are running. The only routing protocol that really does unequal metric load balancing is EIGRP (I omit IGRP because it is no longer actively supported). To get any other routing protocol to put unequal links into the routing table you must fudge the metrics. And if you have fudged the metrics then the load balancing that CEF will do will not effectively use the links.
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