mercredi 22 février 2012
Some reasons to use VSS are to get rid of spanning-tree between the distribution and access layers. You also no longer need to use HSRP. For example, an access switch connecting to your distribution would usually be dual-homed, meaning connecting to two separate distribution switches. With spanning-tree, in most cases, one of the uplinks will be unused for a given vlan. That means if you use 10 Gig uplinks, one is unused and only for redundancy (you can balance vlans to even things out, but that has to be configured). With VSS your access switch would have only one port channel that would actually connect to both distribution switches. From the perspective of the access switch, it’s only connecting to a single switch (even though it’s physically two separate switches). Since we only have one port-channel to the distribution, HSRP or VRRP is not needed. One vlan IP is assigned to the VSS distribution switch, and clients use that as default gw. Load balancing across links is done using the traditional etherchannel hashing algorithm.