From: James Ventre (messageboard@ventrefamily.com)
Date: Wed Mar 02 2005 - 23:04:56 GMT-3
Other DTP requirements:
http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a0080094713.shtml#dtp
The following are some highlights of the protocol:
*
DTP assumes a point-to-point connection, and Cisco devices will only
support 802.1q trunk ports that are point-to-point.
*
During DTP negotiation, the ports will not participate in STP. Only
after the port becomes one of the three DTP types (access, ISL, or
802.1q) will the port be added to STP. Otherwise PAgP, if configured,
is the next process to run before the port participates in STP.
*
If the port is trunking in ISL mode, DTP packets are sent out on VLAN
1, otherwise (for 802.1q trunking or non-trunking ports) they are
sent out on the native VLAN.
*
In desirable mode, DTP packets transfer theVTP domain name (which
must match for a negotiated trunk to come up), plus trunk
configuration and admin status.
*
Messages are sent every second during negotiation, and every 30
seconds after that.
*
Be sure to understand that modes on, nonegotiate, and off explicitly
specify in which state the port will end up. A bad configuration can
lead to a dangerous/inconsistent state where one side is trunking and
the other is not.
*
A port in on, auto, or desirable mode sends DTP frames periodically.
If a port in auto or desirable mode does not see a DTP packet in five
minutes, it will be set to non-trunk.
James Ventre wrote:
If my trunks don't form - that's one of the first things I check.
http://www.cisco.com/en/US/tech/tk389/tk390/technologies_configuration_example09186a0080094784.shtml!--- In this example, the VLAN Trunk Protocol (VTP) domain name is the same
!--- on both sides. This is required for the autonegotiation of the trunk
!--- by the Dynamic Trunking Protocol (DTP).
James
ccie2be wrote:
James,
I thought DTP is completely independent of VTP, domain names, etc.
Have you tested this?
Is domain name included in the DTP negotiation?
Tim
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