Trunk configuration 1

[KSANE]

Dear All;
I have cisco PoE switch (3560G),when I trying to configure trunk port,this Message will appear:

Switch(config)#int gi0/1
Switch(config-if)#switchport mode trunk
Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode.

Regards

 

[Belushi]

Well, that is what you would expect to see. First you need to configure the trunk encapsulation type. Initially it is set to auto. As always, Cisco is the first, and best place to look for the answer on configuration guides:

http://www.cisco.com/en/US/docs/swi...lease/12.2_44_se/configuration/guide/scg.html

 

[vipergg]

If trying to trunk just use. Will work everytime.

switchport encapsulation dot1q
switchport mode dynamic desirable
switchport native vlan X

--- > X is whatever you want use for native.

 

[Belushi]

Won't work everyitme. Depends on the switch on the other side and it's settings. Assuming the switch on the other side is another 3560 and is set to defaults then yes, it will work.

I can see your approach though. One thing I've learned over the years and through my CCIE studies is to assume nothing. Therefore, you can't just gurantee that the trunk will work.

 

[vipergg]

I assumed he was talking cisco on the other side . Forcing the trunk on won't work either if its not done right.

 

[brianinms]

I never ever set a port as dynamic desirable. With me its either an access port or its a trunk port.

 

[Flyers01]

Do it like this you should not have a problem

Switch(config)#int gi0/1
Switch(config-if)#switchport encapsulation dot1q
Switch(config-if)#switchport mode trunk
Switch(config-if)#end

don't use desirable

 

[Belushi]

I am not understanding some you guys and your stances on trunk configurations. Why not use desireable. What's wrong with it? Please tell me. Just because you guys do something one way, doesn't mean it's the only valid way and no one can do something different. That's why I provided the link to the configuration guide for 3560s, this way he can get all applicable methods and decide what is best for him.

 

[vipergg]

Don't use desirable , you obviously have no basis for that statement just a preference. This is right out of a cisco best practices document. If you force it on all it takes to say it is trunking is a layer 1 link and it will say it is trunking when it very well might not be , dynamic protocols get rid of that worry.

Cisco recommends an explicit trunk mode configuration of dynamic desirable at both ends. This mode is the default mode. In this mode, network operators can trust syslog and command-line status messages that a port is up and trunking. This mode is different from on mode, which can make a port appear up even though the neighbor is misconfigured. In addition, desirable mode trunks provide stability in situations in which one side of the link cannot become a trunk or drops the trunk state.

 

[ADB100]

viperegg, I think we have had this discussion before....

Cisco's (current) best practise is NOT to set anythintg to automatic/desirable. Old documents state using Desirable/Desirable, however current best practise is to hard-code trunks BUT know what and where they are...

Have a read of the Campus High Availability SRND here:

http://www.cisco.com/go/srnd

I used to think it was best to leave everything automatic but that just leads to laziness and potential issues through not knowing what should and shouldn't be trunking/channeling etc.

There are benfits in convergence time as well, quite significant if you are deploying VoIP....

My 2-cents...

Andy

 

[vipergg]

Well its still in their catalyst 4500 best practices documents so its whatever anyone is comfortable with . I have problems more than once with forced on trunks that are misconfigured.

 

[brianinms]

I agree with Andy, all the security blueprints clearly state that you should set the port to a trunk or to an access port. Additionally no current switch is shipped as dynamic desirable, last switch I can remember that was shipped that way was the 3524s. You will never have a problem if you set both ports as a trunk. You should always filter the allowed vlans on a trunk link as well.

 

[vipergg]

Won't disagree with you there about filtering the allowed vlans . Whenever you look on this board anyone who is doing any kind fo trunking you never seen any kind of pruning off of allowed vlans , they leave them wide open .

 

[burtsbees]

On one hand, setting the trunks manually will obviously make them trunk, and one must trust that both sides and everything else is set correctly. On the other hand, dynamic desirable sets them only if it works. To me, if it were dynamic desirable in this case, then you would want it to work with other things misconfigured. Forcing a trunk will make you fix everything else...

Burt