ajenks Wed, 07/30/2008 - 07:50
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Thanks. Is this done via round-robin type allocation ? is this done per session or per packet ? I am seeing unfair loading on one of the routes.


By this I mean I see far greater bandwidth throughput and (I believe) far greater number of sessions, on one particular link.

Hieu Cao Wed, 07/30/2008 - 08:53
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Maximum path is 6, not 4 as keeley mentioned above, and the default is actually 1.


For EIGRP, the default load-balance method is per-destination. Per-Packet can be used if you're not using VoIP in your network.







Hi There


Without meaning to be argumentative, I never said that the maximum paths in EIGRP was 4.


What I said was that if (as the OP stated) there are paths to the same destination of equal cost, Then EIGRP will perform equal cost load sharing. The default number of paths EIGRP will use is up to 4. With the maximum number of paths that can be used being 6 (as you pointed out).


If 5 equal cost paths existed and without manual intervention, EIGRP would use 4 of these paths and load share across them.


I am not sure how EIGRP would choose which of the 4 paths to use, though I imagine it will use the four oldest. The paths it learned first. But this is just a guess.


If 2, 3 or 4 equal cost paths existed, then EIGRP would perform equal cost load sharing across all of the available equal cost paths.


As for the default load balancing method, "per destination" will only be used on interfaces where "fast switching" is enabled.


If fast switching is disabled, then all packets are sent to the CPU and are load balanced on a per packet basis.


See this excerpt


"By default, if there are multiple equal-cost paths to a destination the router will load share across up to four paths. Generally with most routing protocols, you can change this in the routing process with the command maximum-paths number and have up to 6 paths. By default, on interfaces where fast switching is enabled, the router will perform per-destination load balancing. If fast-switching is turned off then all packets will be examined by the CPU and be load-balanced on a per-packet basis. The load on the CPU can be extensive. Using Cisco Express Forwarding (CEF), you can choose to load balance on a per-packet or per-destination basis with less impact on the CPU. "


From this web site http://www.rhyshaden.com/eigrp.htm for more information


Best Regards,


Michael

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