Load balancing in EIGRP

[fbarreras]

Came across this statement:

EIGRP automatically load balances across links of equal costs. Whether the traffic is sent on a per-destination or round-robin basis depends on the internal switching within the router.

Could somebody let me know which fashion would be specific to which models/series of Cisco routers? Thanks

[Erick Bergquist]

Hi,

Fast-switching is the default (per destination). (ip route-cache command)

You can disable per-destination and do process-switched (per packet; hits CPU) by doing 'no ip route-cache' on the interface.

CEF is the recommended method to use nowadays. You enable it globally with 'ip cef' and by default it does per-destination. you can configure CEF to do per-packet with 'ip load-sharing per-packet' on the interface.

IOS will equal cost route across 4 paths by default. This can be increased to a max of 6 however. With EIGRP you can use the variance command to do unequal load balancing across multiple paths.

[fbarreras]

Thanks for your response. A follow up question. Does the destination router have to have the same configuration? If not, how does the destination router know in what order the received packets should be reordered?. Sequence numbers? Thanks.

[prafuljaded]

Regarding your follow up question, the destination router works according to its configuration. But its better you have same configuration (like CEF) on all your routers, this helps in case you are running VoIP or Video applications.

[Erick Bergquist]

The destination host puts the packets back together in the right order if they happen to be out of order. The router doesn't do this ... unless the destination is the router. .

[fbarreras]

Thanks for the information.