CEF vs. EIGRP for load balancing

[jason.linden]

Some of our sites have dual PVCs pointing to two different FR T1's on our head-end router, the PVC's have the same port speed, CIR, and the bandwidth command is set to the same for both PVC's, so from EIGRP the paths are equal. My question is how does EIGRP and CEF differentiate in terms of load balancing on a per-packet basis?

I have enabled per-packet on one of the sub-interfaces here is the output for 'sh ip cef detail' for that destination network:

10.0.1.0/24, version 358, per-packet sharing

0 packets, 0 bytes

via 10.75.3.10, Serial0/0.2, 0 dependencies

traffic share 1, current path

next hop 10.75.3.10, Serial0/0.2

valid adjacency

via 10.75.4.10, Serial0/1.2, 0 dependencies

traffic share 1

next hop 10.75.4.10, Serial0/1.2

valid adjacency

25500 packets, 17030273 bytes switched through the prefix

30 second output rate 78 Kbits/sec

My question is why does Serial0/0.2 say 'traffic share 1, current path' but for s0/1.2 it says 'traffic share 1'? What does the current path mean? Does it mean that traffic is only going out the S0/0.2 interface?

One last question... Does CEF need to be enabled on both ends of the Frame to work efficiently?

[ruwhite]

BTW--it's better if you are using the same load sharing mechanism on both ends of the link. And you should definitely try later code, as the CEF algorithms are always being improved/etc.

:-)

Russ

[ruwhite]

Okay--thanks for the correction in the diagram. I don't think per packet needs to be enabled on the fast ethernets, but I would turn it on.

Per prefix accounting counts the packets to any final destination. Non-recursive accounting counts traffic passing through an mtrie node, pretty much--look up traffic matrix statistics on CCO to find out more, since this was designed to fit into that scheme. Prefix length acocunts for the distribution of traffic aomng various prefix lengths within your network--for instance, the amount of traffic being forwarded along /24's vs /16's. This is also designed for some very specific purposes.

At this point, we'll need to take a close look at what you're seeing here--it looks like per packet should be working, but the cef stats don't seem to be showing that. So, try per packet on the inbound ports, and then look at the interface stats to see if they show traffic flowing over both interfaces.

show ip cef not might also be useful to poke around and see if there is a problem with one of the interfaces cef switching packets.

Russ