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multilink different bandwidths

Posted on 2004-09-08
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Last Modified: 2010-04-17
At one location I have 2 point to point full T1's multilinked connected back to the home office - it works great - full 3mb pipe - if one T goes down connectivity stays up on the remaining T1

At another less used location I have 1 point to point T1 back to the home office - works fine.  We are lookign at getting a backup 256k point to point line - question is, could I set up a multilink like the other location even though they would be differing bandwidth - 1.5mb and 256k - that way we could aggregate and at least use the backup line, but it would also be available.
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Question by:mrsmileyns
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13 Comments
 
LVL 11

Expert Comment

by:PennGwyn
ID: 12008199
I would think this might be beyond multilink's capabilities, but if you run EIGRP it can distribute the load and handle the failover for you.

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Author Comment

by:mrsmileyns
ID: 12008223
To set ip up via EIGRP...at the remote location...the 2 T1's can be on the same router in different WIC's or 2 different physical routers, correct?
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LVL 28

Accepted Solution

by:
mikebernhardt earned 125 total points
ID: 12008567
Either one- you can use the variance feature in EIGRP to tell it to load-balance between the 2 links- and it will do it proportionally if you want.

router eigrp 1
      network x.x.x.x
      variance 6
      traffic-share balanced

This would load-balance traffic on all links which are within 6 times of each other (i.e. 256kb and 1.5mb) and balance traffic proportionally.
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LVL 1

Expert Comment

by:stealth188
ID: 12011699
You have to use EIGRP otherwise you will end up with "Pinhole Congestion".
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LVL 79

Assisted Solution

by:lrmoore
lrmoore earned 125 total points
ID: 12012505
You can use two static same-cost routes with no regard to one link being slower than the other.
You can "fool" EIGRP by setting the same bandwidth statement on both interfaces. Remember, this has zero effect on the actual bandwidth, only on the processes that use the knowledge of what you are telling it the bandwidth is.

It's not as elegant as Mike's suggestion because it does not load-balance in proportion to the  bandwidth..


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Author Comment

by:mrsmileyns
ID: 12063814
So lets say right now with the existing full T1 the default route is

0.0.0.0 0.0.0.0 192.168.253.5

192.168.253.5 is the IP on the other end of the point to point T1

If I introduce a new 256k line i could simply add

0.0.0.0 0.0.0.0 192.168.252.5   -  or whatever I set up this new line to be, right?

So this would be the easiest way...and using EIGRP would be the "best" way?  If it is not load balanced in proportion to bandwidth, how would a packet decide which WAN link to take?
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LVL 79

Expert Comment

by:lrmoore
ID: 12063871
With 2 same-cost static routes, the router will use packet-by-packet load balancing without regard to proportion of bandwidth. If you enable CEF, you can load-share per-connection instead of per-packet.
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Author Comment

by:mrsmileyns
ID: 12063945
of the two solutions proposed, which would you do if you were me given the same situation?
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LVL 79

Expert Comment

by:lrmoore
ID: 12064127
If I owned / controlled both ends, I'd go with the EIGRP solution to get the proportional load-sharing.
If I have no control over the other end (someone else owns it and won't set up IEGRP), I would probably not use the 256k link unless the T1 was down. Use it for backup purposes only...
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Author Comment

by:mrsmileyns
ID: 12064181
alright then - when I get the line I'll probably have to submit a new question to help with the EIGRP setup - I control both routers - thanks for being patient with me - I am going to split points here
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LVL 28

Expert Comment

by:mikebernhardt
ID: 12067081
Really you probably have everything you need in this question. Just add a "network x.x.x.x" statement for each classful network on a particular router. Make sure the eigrp AS number is the same on both routers i.e. "router eigrp 1." If you have the same classful network on both sides (say, 10.x.x.x) but a different one in between on the serial links (say, 192.168.x.x), then be sure to add "no auto-summary" under router eigrp 1, on both sides. That's about it along with the variance stuff from earlier.
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Author Comment

by:mrsmileyns
ID: 12067420
Yeah - it seems that way...setting this up seems very simple as far as I can see - I haven't even ordered the 256k line yet - so it will be a little while before I am good to go - but my boss just decided he wants to do it.

After it is done, what can I do to make sure it is working, make sure it is load balancing and packets are going over both lines?
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LVL 28

Expert Comment

by:mikebernhardt
ID: 12068162
If you type "show ip route" on both routers you should see both paths available, but with different metrics. Normally you would only see 2 paths if the metrics were equal.
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