OSPF over a lacp link

[soumenG]

Hi Team

I am facing some issue in my topology where i configured ospf over a 2 port lacp link in the cpe router and i want loadbalance(dl/ul) on both of the link but the ospf is working as failover mechanism, and i am not able to balance traffic on both of the link. Attaching the snap of my simple topology. I dont know where i am missing, Please help me on this.

[MHM Cisco World]

Only make sure yout port channel member all P not S 

Do show port-channel summary 

Or 

Do show etherchannel summary 

Check the status of port channel

If there is issue change mode of port channel from active to ON in both side 

[soumenG]

Hello @MHM Cisco World 

Yes it is showing "P" in the show etherchannel summary output and all the links are bundled together.

[M02@rt37]

Hello @soumenG,

Please verify that both ports are active and bundled together using the LACP protocol.

To enable load balancing in OSPF, you need to enable ECMP. This allows OSPF to distribute traffic across multiple equal-cost paths. To do this, you can configure the [maximum-paths] command under the OSPF process on the CPE router.

[MHM Cisco World]

No need ecmp port channel represent one interface i.e. one path 

[M02@rt37]

Hello @MHM Cisco World 

Instead of relying on OSPF's built-in load balancing, he can use other mechanisms like per-packet or per-flow load balancing provided by the port channel technology itself (e.g., LACP). This can distribute traffic across the member links of the port channel without relying on OSPF for load balancing.

Thanks for correct me.

[MHM Cisco World]

If I am correct' the port channel need config mode ON not active router not support mode active which meaning send/receive lacp.

[M02@rt37]

@MHM Cisco World 

Yes!

[soumenG]

Thanks for the reply M02@rt37 

I need to rely on ospf because I am using broadcast network and I shared only some part of the network.

The CPE is also connected to another ospf speaking router with /30 network which is connected to another L2 device and the L2 is connected towards MLS1. When the primary lacp link fails CPE is choosing the secondary path which I didn't mentioned here, but all I want, whe the primary path(lacp link) is up it should be use as ecmp, but unfortunately the CPE router is using only one LINK for ul/dl when both the links are up under etherchannel.

[MHM Cisco World]

OK, the per-packet of CEF is L3 
let down one level to L2 load sharing 
change the hash algorithm for PO to include port, and when you test use one time ping and other time telnet.

[Joseph W. Doherty]

As already mentioned by others, a port channel, regardless of the number of active links, only "sees" one link.  However, I recall bandwidth of a port channel can change with number of active links, and if using OSPF auto costing, OSPF might then change its best path.

LB across a port channel is done per port channel LB algorithm, and on Cisco's Ether channel, to my knowledge flows are not split across links (like packet-by-packet CEF).

[soumenG]

Dear all

Thanks for your reply..

It is the CPE router which is not compatible with Cisco hashing algorithm I think so. When using only layer 2 load balancing only one link is sending and other is receiving that is case I observed without routing.

[MHM Cisco World]

I will run small lab test this behavior. 

Thanks 

MHM

[MHM Cisco World]

[Joseph W. Doherty]

To or from the Cisco router?

Cisco Etherchannel load balancing only applies to egress traffic.  It also works with L2 or L3 traffic.

OSPF ECMP, using distinct L3 links, also only applies to egress traffic, but likely any platform supporting OSPF will also support ECMP.

As both Etherchannel and OSPF ECMP LB, is one better than the other?

Personally, I would lean toward Etherchannel because it offers LB criteria choices, precludes the need for another subnet allocation and it's LSA/network adding to OSPF's load, and it's easier to add links.

If the CE router doesn't support LB, as you desire, but OSPF does, then you have a very good reason to use it.