vss uplink from a closet

[DARYLE DIANIS]

I believe I understand that MEC on a VSS can be Layer 2 or Layer 3.  Is that correct?  Is one better than the other?  For simplicity, it seems a Layer 2 link might be easier.  Are there pro's and con's?

thanks,                  

[Reza Sharifi]

MEC with VSS is layer-2:

Q. What is multichassis EtherChannel?

A. Multichassis EtherChannel (MEC) is a Layer 2 multipathing technology.  This form of EtherChannel allows a connected node to terminate the  EtherChannel across the two physical Cisco Catalyst 6500 Series Switches  that make up the VSS leading to creating simplified loop-free Layer 2  topology. Using MEC in VSS topology results in all links being active  and at the same time provides for a highly available topology without  the dependency of Spanning Tree Protocol. With the introduction of  12.2(33)SXI, the virtual switching system supports a maximum number of  512 MECs.

More info here:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps9336/prod_qas0900aecd806ed74b.html

HTH

[DARYLE DIANIS]

thanks for the info, I've been reading from this document, too:

http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/VSS30dg/VSS-dg_ch3.html#wp1102944

and it discusses Layer 2 and Layer 3 MEC. If a person had a choice between using Layer 2 or Layer 3 uplinks to a VSS, which choice would be better or is it one of those "it depends" kind of thing.

thanks,

[Reza Sharifi]

Usually when you uplink your access devices to VSS, it is layer-2 portchannel (MEC) from the access switch to both 6500 switches with SVIs on them. This eliminates VRRP, HSRP, Spanning tree etc....

HTH

[Joseph W. Doherty]

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Posting

Generally, the VSS uplink would be whatever you might have used if VSS wasn't available and you are working with a single physical device.  I.e. if you would have used L2, VSS uplink is likely to still be L2.  If you would have used a L3, VSS uplink is likely to still be L3.