Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

per-destination CEF and EIGRP unequal-cost paths

Hello!

Does CEF supports per-destinaltion unequal-cost load balancing?

And how does it distributes sessions among unequal-cost EIGRP paths?

Thanks in advance!

6 REPLIES

Re: per-destination CEF and EIGRP unequal-cost paths

Hello,

I think the only options CEF has is per-destination load balancing (which is the default), and per-packet load balancing. So if you turn on CEF together with EIGRP variance configured, traffic will be routed equally amongst the routes installed in the routing table.

Or, as CCO puts it:

When you work with CEF, you could ask: Who does the load balancing, CEF or the routing protocol used? The way in which CEF works is that CEF does the switching of the packet based on the routing table which is being populated by the routing protocols such as EIGRP. In short, CEF performs the load-balancing once the routing protocol table is calculated.

With EIGRP, you can actually tell the load balancing mechansim to keep in mind the cost of each path:

'EIGRP not only provides unequal cost path load balancing, but also intelligent load balancing, such as traffic sharing. In order to control how traffic is distributed among routes when there are multiple routes for the same destination network that have different costs, use the traffic-share balanced command. With the keyword balanced, the router distributes traffic proportionately to the ratios of the metrics that are associated with different routes'

Does that answer your question ?

Regards,

GNT

New Member

Re: per-destination CEF and EIGRP unequal-cost paths

Hello GNT,

thanks for your valuable reply.

I'll put my question in other way. Suppose a router has two EIGRP routes with costs of 1000 and 2000 respectively. Then I start 30 IP sessions all with different source/destination pairs. Does CEF distribute 20 sessions to the first route, and 10 sessions to the second?

New Member

Re: per-destination CEF and EIGRP unequal-cost paths

since CEF is enabled, i think cef will distribute 15 sessions to first route and 15 to other as CEF does equal load balancing along with eigrp..

correct me if i am wrong

New Member

Re: per-destination CEF and EIGRP unequal-cost paths

Hi,

Here is the link to one of the documents which give us the answer:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml#cef

//Mikhail Galiulin

New Member

Re: per-destination CEF and EIGRP unequal-cost paths

Hello Mikhail!

Thanks for your reply.

The document you provided states that CEF doesn't load balance traffic on interfaces of different physical types. But I have interfaces of the same physical type: both serials. Will it load balance IP sessions as I wrote above (10/20)?

New Member

Re: per-destination CEF and EIGRP unequal-cost paths

yes , it will load balance like 10/20.

193
Views
0
Helpful
6
Replies