DTP Negotiation for Dummies
Warning: there is nothing formal about this post, just a way to help me (and maybe you, who knows) remember DTP port states:
Dynamic Desirable: “Hey, I want to trunk and I’m letting everyone know” (3550’s are DD by default)
Dynamic Auto: “I want to trunk, but I’m not announcing it. BUT! I’ll answer DTP trunking requests” (3560’s are DA by default)
DD + DA = Trunk (And use ISL unless configured otherwise — assuming Cisco switches)
DD + DD = Trunk
DA + DA = No Trunk for You!
You can disabled DTP by either:
- Setting the interface to static access using the switchport mode access command
- Turn off DTP all together with switchport nonegotiate
September 15, 2009 at 3:54 pm
Another neat thing about nonnegotiate and DTP (or DISL) is a case covered in Kennedy Clark’s Cisco LAN Switching (page 544). If I have two VTP domains and I want to get a trunk going between the two, they won’t come up! Reason: different VTP domain name in the DTP/DISL request. How does one make this situation work? “on” or “nonnegotiate”.
Kind of neat, figured I’d share.