EPAgP on 3750X with VSS

Question

Hello all,
I'm right now testing VSS dual active detection using EPAgP on a 3750X Stack.
I've noticed that CrossStack Etherchannel is ONLY supported within a Stack if both aggregated links belongs to the same unit...so if I use "desirable" mode all the links should be connected in example to unit1. This is what I would like to avoid having a channel with aggregated interfaces on the same unit of the Stack (very strange restriction moreover considering PAgP is Cisco proprietary).
What about using channel mode ON? Forcing the ports to belong to a channel without negotiating can be configured on all the units of a Stack with no restricitons...Is this gonna work?  Or EPAgP requires all the ports of the Etherchannel on both the VSS and Stack units configured as desirable?
Thanks a lot for sharing ideas...
Omar

Answer 1

Hi Omar, 
Indeed the limitation comes from the 3750 which does not support cross-stack PagP (so ePagp will not be supported as well in a cross-stack fashion).
As Glen stated LACP is recommended (but you will loose VSS dual active detection).
Otherwise you will have indeed to use ePagp through the same unit. 
It is document by the VSS guide => http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/VSS30dg/campusVSS_DG/VSS-dg_ch4.html#wp1129136 (look at Enhanced PAgP Support  part) :
"PAgP is supported in all platforms except the Cisco Catalyst 37xx stack configuration in which cross-stack EtherChannel (LACP) is required to have MEC-connectivity with the VSS. Because cross-stack EtherChannel does not support PAgP, it cannot use enhanced PAgP for dual-active detection. A common approach to resolve this gap in support is to use two EtherChannel links from the same stack member. This solution is a non-optimal design choice because"
Best regards.
​Karim