From: Anthony Sequeira (terry.francona@gmail.com)
Date: Wed Apr 20 2005 - 15:14:55 GMT-3
Here is what I know to be true from the documentation regarding this
interesting discussion (not had time to actually verify with a sniffer
- but I trust in my sources on this one).
If you are asked to "statically" configure the port as a trunk - you simply use:
switchport trunk encap xxxx
switchport mode trunk
Yes - you are still sending and receiving DTP frames - but that is OK
- you are going to trunk period - regardless of the config on the
other side (although, obviously if it is incompatible you do not have
a functional trunk link.) You should contrast this mode to:
switchport mode dynamic auto
or
switchport mode dynamic desirable
If you are asked to not use DTP - then the command:
switchport nonegotiate
comes into play! Now you are no longer activity participating in the
DTP process.
As a best practice in production - I use nonegotiate all the time -
but on the lab - I am merely going to configure what they specifically
ask me for.
On 4/20/05, Mark Lasarko <mlasarko@co.ba.md.us> wrote:
> I agree Dennis,
> I rarely see this included in any solutions and wonder why?
>
> I don't have the NMC solutions, but of the others I do have I have
> only seen this used when DTP is specifically mentioned.
>
> Setting the mode to trunk only seems to disable the Access timer.
> The Hello timer still runs until you issue 'switchport noneg'
>
> Please note that I have not put a sniffer on the port to confirm
> DTP packets are actually still being sent as opposed to just
> listening?
> Can anyone confirm this??
>
> ************************************************
> interface FastEthernet0/48
> switchport trunk encapsulation dot1q
> switchport mode dynamic desirable
> !
>
> Rack1SW2#
> Rack1SW2#sh dtp int fa0/48
> DTP information for FastEthernet0/48:
> TOS/TAS/TNS: TRUNK/DESIRABLE/TRUNK
> TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
> Neighbor address 1: 000000000000
> Neighbor address 2: 000000000000
> Hello timer expiration (sec/state): 8/RUNNING
> Access timer expiration (sec/state): 260/RUNNING
> Negotiation timer expiration (sec/state): never/STOPPED
> Multidrop timer expiration (sec/state): never/STOPPED
> FSM state: S6:TRUNK
> # times multi & trunk 0
> Enabled: yes
> In STP: no
> <statistics omitted>
>
> Rack1SW2#config t
> Enter configuration commands, one per line. End with CNTL/Z.
> Rack1SW2(config)#int fa0/48
> Rack1SW2(config-if)#switchport trunk encap dot1q
> Rack1SW2(config-if)#switchport mode trunk
> Rack1SW2(config-if)#end
> Rack1SW2#sh dtp int fa0/48
> DTP information for FastEthernet0/48:
> TOS/TAS/TNS: TRUNK/ON/TRUNK
> TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
> Neighbor address 1: 000000000000
> Neighbor address 2: 000000000000
> Hello timer expiration (sec/state): 20/RUNNING
> Access timer expiration (sec/state): never/STOPPED
> Negotiation timer expiration (sec/state): never/STOPPED
> Multidrop timer expiration (sec/state): never/STOPPED
> FSM state: S6:TRUNK
> # times multi & trunk 0
> Enabled: yes
> In STP: no
> <statistics omitted>
>
> Rack1SW2#config t
> Enter configuration commands, one per line. End with CNTL/Z.
> Rack1SW2(config)#int fa0/48
> Rack1SW2(config-if)#switchport noneg
> Rack1SW2(config-if)#end
> Rack1SW2#sh dtp int fa0/48
> 1w6d: %SYS-5-CONFIG_I: Configured from console by console
> Rack1SW2#sh dtp int fa0/48
> DTP information for FastEthernet0/48:
> TOS/TAS/TNS: TRUNK/NONEGOTIATE/TRUNK
> TOT/TAT/TNT: 802.1Q/802.1Q/802.1Q
> Neighbor address 1: 000000000000
> Neighbor address 2: 000000000000
> Hello timer expiration (sec/state): never/STOPPED
> Access timer expiration (sec/state): never/STOPPED
> Negotiation timer expiration (sec/state): never/STOPPED
> Multidrop timer expiration (sec/state): never/STOPPED
> FSM state: S6:TRUNK
> # times multi & trunk 0
> Enabled: yes
> In STP: no
> <statistics omitted>
>
> Personally, I don't care for *any* excess traffic, therefore it
> would seem like a best practice to me, for the lab or otherwise.
> ~M
>
> >>> "Dennis J. Hartmann" <dennisjhartmann@hotmail.com> 4/20/2005
> 1:13:44 PM >>>
>
> If I'm required to statically set all trunk ports to dot1q, I'll
> be
> turning off DTP with the switchport nonegotiate command.
>
> I didn't notice this in the NMC solutions. Any ideas?
>
> Sincerely,
>
> Dennis J. Hartmann
>
> White Pine Communications
>
> dh8@pobox.com
>
> CCSI#23402/CCIP/CCNP/CCDP/CCNA/CCDA
>
> Cisco IP Voice Support & Design Specialist
>
> Cisco Optical, VPN & IDS Specialist
>
> MCSE
>
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