Ethernet Switches & Routers

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Contributor
Posts: 44
Registered: ‎07-08-2011

What is danger of using "trunk hash-options include-layer2" for LACP connection

Here is our config. We would like more balanced utilization across two 1 gig links trunked together using LACP. Someone suggested using the "trunk hash-options include-layer2" command, but:

(A) Will that help our situation?
(B) Why wouldn't this be on by default and what is danger if enabled?

We are replicating SAN to SAN traffic between cities, but between two sets of stacked FCX switches are our provider's cisco devices, hence why they said we had to use LACP. This is a private link, not going over WAN. We have multiple VLANs that span this traffic.

I should mention that we configured ports 1/1/4 and 2/1/4 to be a member of the group ahead of time so that all we'd have to do is connect them to go to 3x 1Gbps trunk via LACP. That's why I pasted that part of the config. Also, 2/1/3 appears to not have the spanning-tree line because it won't let you configure that port since it's part of the trunk.

ver 07.1.00aT7f3
!
stack unit 1
  module 1 fcx-48-port-management-module
  module 2 fcx-cx4-2-port-16g-module
  priority 128
  stack-port 1/2/1 1/2/2
stack unit 2
  module 1 fcx-48-port-management-module
  module 2 fcx-cx4-2-port-16g-module
  priority 128
  stack-port 2/2/1 2/2/2
stack enable
stack mac asdf.asdf.asdf.asdf

....

interface ethernet 1/1/3
port-name RepPorts
dual-mode
spanning-tree 802-1w admin-pt2pt-mac
link-aggregate configure key 20000
link-aggregate active
!
interface ethernet 1/1/4
port-name RepLink4
dual-mode
spanning-tree 802-1w admin-pt2pt-mac
link-aggregate configure key 20000
link-aggregate active
!

interface ethernet 2/1/3
link-aggregate configure key 20000
link-aggregate active
dual-mode
!
interface ethernet 2/1/4
dual-mode
spanning-tree 802-1w admin-pt2pt-mac
link-aggregate configure key 20000
link-aggregate active
!

Occasional Contributor
Posts: 11
Registered: ‎11-25-2012

Re: What is danger of using "trunk hash-options include-layer2" for LACP connection

With SAN-to-SAN replication I don't think the load balancing mechanisms on LACP will help much. Reason being is that the session parameters that are used to decide between paths (e.g. MAC/IP source & destination/port information) is usually pretty static. In my experience SAN replication tends to only be single streamed by the SAN itself as well which further complicates the matter.

If you can get the SAN replication software to create multiple streams you can start balancing using the layer 4 source/destination port details and get some use out of it then. Otherwise I wonder if you'd be better off using ECMP if you're running layer 3 across the links.

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