Load balancing links

Unanswered Question
Apr 6th, 2009

To KISS it I have a 6509 connected to 2 7206's..One MPLS and one is AVPN. Far end is 2 2811's and a 3560 layer 3 switch.

We are running a mGRE tunnel across the AVPN so the 6500 to each remote router shows a equal EIGRP path. And both links are carrying traffic. Problem is one is hit a lot harder then the other. I have been reading and I think it might be how CEF does load-balancing, per-packet vs per-dest..But the 6509 will not let me do the per-packet command on the routed interfaces toward the 7206.

1st will the 6509 do per packet load-balancing in CEF..Traffic out toward the core is balanced well but from the 6509 back isn't.

2. If it is possible how do you enable it?

I have this problem too.
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lamav Mon, 04/06/2009 - 15:51

"will the 6509 do per packet load-balancing in CEF"

Per-destination load balancing is enabled by default when you enable CEF. To use per-destination load balancing, you do not perform any additional tasks once you enable CEF.

For per-packet load sharing, under interface configuration mode, execute the following command:

ip load-sharing per-packet

HTH

Victor

markayash Mon, 04/06/2009 - 16:28

That's what I found but it won't work? What am I missing..It's a 6509 with ver 12.2 (18)

OSH-NEW-CORE-6509(config-if)#ip load-sharing ?

per-destination Deterministic distribution

lamav Mon, 04/06/2009 - 17:09

Ok, so heres a stupid question, do you have CEF enabled globally?

If so, you may have to first disable per-destination load balancing on the interface before it allows you to configure per packet.

Go under the interface configuration mode and do a

"no ip load-sharing per-destination"

Then see if the per-packet option opens up....

lamav Mon, 04/06/2009 - 18:46

This statement sounds weird:

"On the Catalyst 6000 series, the Cisco IOS Cisco Express Forwarding ip load-sharing per-packet, ip cef accounting per-prefix, and ip cef accounting non-recursive commands on the MSFC2 apply only to traffic that is Cisco Express Forwarding-switched in software on the MSFC2."

I thought that CEF switching is a function of the ASIC hardware that it leverages. I always thought that the CEF table, which is a derivative of the route table, and the adjacency table, are both created in the control plane, in software, but are "downloaded" and reside in the data plane, in a hardware-based L3 forwarding engine.

I mean, thats one of the first things we hear: CEF is fast because it is done in hardware. The CEF FIB and Adjacency tables utilize the architecture of parallel data structures in a TCAM to perform fast lookups.

What am I not understanding?

Victor

Giuseppe Larosa Mon, 04/06/2009 - 22:57

Hello Mark,

what supervisor model is in your chassis ?

You have sup2/MSFC2 or SUP720 ?

the sentence applies to the first.

I've tried on a sup720 3B with the same results

int gi1/5

router(config-if)#ip loa

router(config-if)#ip load-sharing ?

per-destination Deterministic distribution

router(config-if)#^Z

So it looks like that CEF implementation on C6500 doesn't support per-packet load balancing.

Hope to help

Giuseppe

markayash Tue, 04/07/2009 - 03:29

I have supv 720's..One question I have is can I disable CEF for WAN routing? Would that let EIGRP do the load sharing?

Giuseppe Larosa Tue, 04/07/2009 - 05:14

Hello Mark,

you cannot disable CEF on a C6500.

EIGRP can be of help in case of unequal cost paths but doesn't provide any advantage in this scenario.

if there are only few flows that use most one link you can divert some of them using PBR applied inbound on the internal interface in order to get some load sharing

Hope to help

Giuseppe

markayash Tue, 04/07/2009 - 05:24

Yeah it's a remote site across the WAN and seems to favor one side. Today I am summarizing the class C vlans into a class B..Might remove the statement off eigrp, what I read about CEF if it like different ip's..Today it see's a 10.177.0.0 as the remote site in the routing table.

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