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dathaide
Beginner

EIGRP and unequal cost load balancing

hi

I have a remote site current connected via a 3640 (router on a stick lets call it 3640A) to Headquaters via 3 T1's. The 3640 connects over ATM interface to an IGX which carries the WAN traffic to headquaters via the 3 T1's mentioned.

What i need to accomplish---Since this is one of our very critcal sites i have been asked to come up with a plan to provide redundacy in the event of a 3640 failure and an IGX failure at the remote site.

My solution is to add a second 3640 (lets call it 3640B) and make it a hsrp peer to 3640A and since we are running eigrp i planned on using the "variance command" on the router process and the track command (still testing) on the hsrp groups such that if one of the interfaces say the ATM goes down hsrp will switch also. Now the WAN link from 3640B to head quaters is going to be a straighforward. It is a just one T1 connected point to point from the router 3640B to headquaters. I plan on terminating this T1 at headquaters on a different router.

I understand that the variance command will take care of load balancing from the remote to headquaters but i am afraid of the return back. I understand that for this scenario to work i will have to put a variance command on the router process at headquaters too. In doing so will i not effect the whole eigrp router process at headquaters for my other sites too or will it only effect the unequal costs path to the remote site ???????/

thanks

3 REPLIES 3
donewald
Frequent Contributor

The Variance command will effect the entire process. So either you'll need a separate process or another way of doing this. You'd still have your redundancy gained with the architecture mentioned without using the variance command within your EIGRP process.

Hope this helps you,

Don

thanks for your reply so in effect for eigrp will load balane across unequal paths even without the variance command but it may not work the way i want correct which is max traffic on the 3T1 side and min on the one T1

thanks

donewald
Frequent Contributor

No, without the Variance Command EIGRP will only load share with equal cost paths. I mentioned you would have your redundancy that you wanted, not the load sharing you were after. EIGRP would still allow a slower cost link to be put into the routing table when the better went away. So, all traffic would be on your 3T1's (assuming MLPPP or the link) which would be a better cost than the other.

Hope this clarifies,

Don