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vss uplink from a closet

DARYLE DIANIS
Level 1
Level 1

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,                  

4 Replies 4

Reza Sharifi
Hall of Fame
Hall of Fame

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

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,

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
Hall of Fame
Hall of Fame

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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.

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