We assessed VSS performance with three sets of tests measuring fabric bandwidth and delay, failover times, and unicast/multicast performance across a network backbone.

For all tests described here, we configured a 10,000-line access control list (ACL) covering layer-3 and layer-4 criteria and spot-checked that random entries in the ACL blocked traffic as intended. As a safeguard against users making unauthorized changes, Cisco engineers also configured access and core switches to re-mark the diff-serve code point (DSCP) in every packet, and we verified re-marking using counters in the Spirent TestCenter traffic generator/analyzer. Cisco also enabled NetFlow traffic monitoring for all test traffic.

To assess the fabric bandwidth and delay, the system under test was one pair of Cisco Catalyst 6509-E switches. Cisco engineers set up a virtual switch link (VSL) between the switches, each equipped with eight WS6408 10G Ethernet line cards and one Virtual Switching Supervisor 720-10G management/switch fabric card. That left a total of 130 10G Ethernet test ports: Eight on each of the line cards, plus one on each of the management cards (we used the management card's other 10G Ethernet port to set up the virtual link between switches).

Using the Spirent TestCenter traffic generator/analyzer, we offered 64-, 256- and 1518-byte IPv4 unicast frames on each of the 130 10G test ports to determine throughput and delay. We measured delay at 10% of line rate, consistent with our practice in previous 10G Ethernet switch tests. The Spirent TestCenter analyzer emulated 100 unique hosts on each port, making for 13,000 total hosts.

In the failover tests, the goal was to compare VSS recovery time upon loss of a switch with recovery using older redundancy mechanisms.

This test involved three pairs of Catalyst 6509 switches, representing the core, distribution and access layers of an enterprise network. We ran the failover tests in three configurations. In the first scenario, we used legacy redundancy mechanisms such as rapid spanning tree and hot standby routing protocol (HSRP). Then we ran two failover scenarios using VSS, first with a virtual link on the distribution switches alone, and again with VSS links on both the distribution and core switches.