Wednesday, July 29, 2009

Vlan Trunking Protocol

So I took a refresher on Vlan Trunking Protocol (VTP) tonight. Here are some of the commands that I saw:
  1. (config)vtp mode
  2. (config)vtp password
  3. (config)vtp domain
  4. (config)vtp pruning (only actually have to run on 1 "server" device in the domain)
  5. show vtp status
  6. show vtp counters
  7. show vtp password
There are 2 versions of VTP, 1 and 2. Couple of differences in that version 1 devices functioning in transparent mode will forward advertisements to downstream switches only if the forwarding device and d0wnstream devices domain name, and version number match. Version 2 devices functioning in transparent mode will forward information across a trunk port even if the domain names do not match. Version 2 also has support for token ring networks.

Finally, VTP advertisements are multicasts that are not sent out every port on the switch. They are actually sent out of trunk ports only. There are 3 types of VTP advertisements; summary, subset, and client.

Summary Advertisements are transmitted by VTP servers
every 5 minutes, or upon a change in the VLAN
database. Information included in the summary
  1. VTP domain name and version
  2. Configuration revision number
  3. MD5 hash
  4. Timestamp
  5. Number of subset advertisements that will follow this advertisement

Subset Advertisments tell whether a vlan has been created, deleted, activated, or suspended; and will give the name, MTU, and type of VLAN.

Client advertisements are actually clients requesting vlan information. A server will respond to this request with a summary and subset advertisement.

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