ECMP VS L3-MEC

[zekebashi]

Hello, 

Which method is the preferred method when connecting uplinks between the distribution and core layers? Is ECMP (L3 individual links) preferred over L3-MEC? The distribution and core layers are configured in VSS. 

Thanks in advance. 

Best, ~zK 

[Reza Sharifi]

Hi,

If both layers are VSS, you want MEC. See link:

https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/VSS30dg/campusVSS_DG/VSS-dg_ch3.html

HTH

[zekebashi]

Thanks for the quick response! 

I've reviewed that document and also another document (attached. In the attached document, I become confused. One page 21 it recommends using Full-Mesh ECMP and on page 31 it recommends to use L3-MEC. 

What are your thoughts? 

Best, ~zK 

[Reza Sharifi]

Are you planning for layer-2 or layer-3 between distro and core?

HTH

[zekebashi]

L3 between the Distribution and Core. 

Best, ~zK 

[Reza Sharifi]

MEC-L3 should work. See page 29 in this document.

https://www.cisco.com/c/dam/global/da_dk/assets/docs/presentations/VSS_0109.pdf

MEC links on both switches are managed
by PAgP or LACP running on the ACTIVE
switch via internal control messages
All the rules and properties of EtherChannel
applies to MEC such as negotiation, link
characteristics (port-type, trunk), QoS, etc.

Do not use “on” and “off” options with
PAgP or LACP protocol negotiation
PAgP—Run Desirable-Desirable with MEC links
LACP—Run Active-Active with MEC links

L2 MEC enables loop free topology and
doubles the uplink bandwidth as no links
are blocked

L3 MEC provides reduced neighbor
counts, consistent load-sharing (L2 and
L3) and reduced VSL link utilization for
multicast flows