VSS or Etherchannel

[tomjansen1]

Hi All,

Please could somebody let me know what differences are between VSS and Etherchannel ? From what I understand, I still need to configure a channel-group on interfaces for VSS anyway.

The only difference I can see is that VSS creates a logical switch rather than just a logical link bundle.

Thanks,

Tom

[Dennis Mink]

I think you have alrweady answered your own question. the VSS can be considered a virtual switch, so a port channel across two physical switches, is redundant against one of the switches going down,

[tomjansen1]

Thanks Dennis, I just wanted to confirm !

So, VSS just adds additional redundancy ?

[Dennis Mink]

Yes it adds another layer of redundancy, PROVIDED its using a port channel, with a link into each physical switch

groeten

[pieterh]

VSS on its own can function over a single link.

BUT....  VSS is a way to create a redundant pair of switches to act as a single switch

from this pont of view it is also "necessary" to make the VSS link redundant (etherchannel)!

connecting a third switch with an etherchannel to both members of this virtual switch does not create a spanning-tree loop

as would be with two switches without VSS AND an etherchannel between them.

[Joseph W. Doherty]

Although Etherchannel is almost always used with VSS (and often should be), they are different and either can be used without the other, although, again, Etherchannel is almost always used with VSS (if it's not, often there's not good reason to use VSS).

Yes, as you note, VSS configures one logical device (you write "switch", but remember it can be L2 or L2/L3 switch). This allows you to Etherchannel between two different physical platforms that host the VSS. While Etherchannel provides redundancy if a link fails, VSS provides redundancy if a device fails. Both also can increase bandwidth throughput.

The "gotcha" with Etherchannel, often is effective load balancing across links. The "gotcha" with VSS, is chassis affinity and avoiding inter VSS traffic flows, except for VSS member component failures (and for that, you need to be plan for how much traffic will use the inter member links [and possibly loss of custom QoS]).