4500X VSS Pair with MEC

[Mokhalil82]

Hi Guys 

I am new to setting up vss on a 4500x and MECs so just want to know if Im on the right lines.

A client has a stack on 3750 switches which are eol so I need to replace them with 2 stacks of 3750x switches but then also introduce 2 x 4500x as the core configured as a VSS Pair. So I will have:

                                     4500x VSS Pair

                                    |                          |

                       3750 Stack            3750 Stack

Im going to have 2 x 10gig uplinks from each 3750 stack one going into each 4500x. Are these uplinks configured as a Multi-Chassis Etherchannel or a normal port-channel. Ive configured port channels before but someone mentioned I should use MECs instead

Any help will be much appreciated.

[M SEB · Accepted solution]

Hi,

Indeed, you will need Multi-chassis etherchannel in this case.  MEC is vSS terminology for etherchannel terminating on each side of the VSS pair. The configuration of it however is the same.

This will give something like that on the VSS cluster : 

interface Port-channel41
 description TO_STACK1
 switchport
 switchport mode trunk
 switchport nonegotiate

interface TenGigabitEthernet1/1/3
 description TO_STACK1_TE1/1/1
 switchport mode trunk
 switchport nonegotiate
 udld port aggressive
 channel-protocol lacp
 channel-group 41 mode active

interface TenGigabitEthernet2/1/3
 description TO_STACK1_TE1/1/2
 switchport mode trunk
 switchport nonegotiate
 udld port aggressive
 channel-protocol lacp
 channel-group 41 mode active

The above commands apply for the 3750x stack side. LACP should be changed to passive mode however. Note that I choose to use LACP in this case. I could also be using mode ON. 

On the 3750 stack sides, if your planning to put your uplink on different stack members, then you'll have cross-stack etherchannel on your 3750 side. PaGP is not supported on cross-stack etherchannel on this platform :

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/69979-cross-stack-etherchannel.html#lacp

That's a pitty because in VSS case, PaGP allows for detecting dual-active failures and avoid them. 

you'll rather have to find another technique for dual-active problems. 

HTH

M S

[Mokhalil82]

Hi 

Thanks for the response, On the 3750 stacks I was planning to uplink to different stack members. Will it work if I just use channel-group mode ON on both ends

[M SEB]

Yes mode ON will work without any problem. 

Since you're not going to use PaGP, make sure you implement a dual-active detection mechanism to avoid split-brain syndrom.

Following link explains fast hello and how to implement it:

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/VSS30dg/campusVSS_DG/VSS-dg_ch4.html#wp1095735

HTH