Describing High Availability in Multilayer Switching
High availability: access layer best practices

When deploying the Campus Infrastructure module, adopting best practice recommendations at the access layer means providing a highly available and deterministic Layer 2 network. It is generally assumed that High Availability in the Access layer will be accomplished through the implementation of link redundancy between access and distribution layers with the STP protocol managing the use of those links. Redundant links to individual user devices is not typical.

These are best practices to follow when establishing highly available access Layer devices.

  • Limit VLANs to a single access switch or switch stack. Spanning VLANs across switches may be necessary in some instances but should be avoided if at all possible.
  • Leave the Spanning Tree Protocol active if there are no redundant Layer 2 links in the network. This will guard against the attachment of rogue switches.
  • Rapid spanning tree is preferred to keep convergence times to 1-2 seconds.
  • Setting trunks permanently on, to avoid auto-negotiation and security issues.
  • If two different version of Cisco software exist at either end of a trunk link ensure that trunk parameters and manually set to match on another.
  • VTP can be disabled or run in transparent mode only
NOTE:

Consider using multilayer switches and routing at the access layer to avoid the use of spanning tree and minimize convergence time.