2960 will not allow "switchport trunk encapsulation dot1q" CLI

[stepnharp]

I have a Cisco 2960 switch that is not allowing me to setup switchport trunk encapsulation dot1q on a trunking interface.

The show capabilities shows that the interface can use 802.1q, but when I try to CLI the command the work encapsulation is not an option.

Please advise with a solution.

Thanks, S

Model - WS-C2960G-24TC-L  

SW Version - 12.2(44)SE6          

SW Image - C2960-LANBASEK9-M

S1#

S1#sh int gi0/23 capabilities

GigabitEthernet0/23

Model:                 WS-C2960G-24TC-L

Type:                 1000BaseLX SFP

Speed:                 1000

Duplex:               full

Trunk encap. type:     802.1Q

Trunk mode:           on,off,desirable,nonegotiate

Channel:               yes

Broadcast suppression: percentage(0-100)

Flowcontrol:           rx-(off,on,desired),tx-(none)

Fast Start:           yes

QoS scheduling:       rx-(not configurable on per port basis),

                         tx-(4q3t) (3t: Two configurable values and one fixed.)

CoS rewrite:           yes

ToS rewrite:           yes

UDLD:                 yes

Inline power:         no

SPAN:                 source/destination

PortSecure:           yes

Dot1x:                yes

Multiple Media Types: rj45, sfp, auto-select

S1#

S1#

S1#

S1(config-if)#switchport ?

access         Set access mode characteristics of the interface

backup         Set backup for the interface

block         Disable forwarding of unknown uni/multi cast addresses

host           Set port host

mode           Set trunking mode of the interface

nonegotiate   Device will not engage in negotiation protocol on this

                 interface

port-security Security related command

priority       Set appliance 802.1p priority

protected     Configure an interface to be a protected port

trunk         Set trunking characteristics of the interface

voice         Voice appliance attributes

S1#

S1#

S1#

S1(config-if)#switchport trunk ?

allowed Set allowed VLAN characteristics when interface is in trunking mode

native   Set trunking native characteristics when interface is in trunking

           mode

pruning Set pruning VLAN characteristics when interface is in trunking mode

S1#

S1#

S1#

[daniel.dib · Accepted solution]

Newer devices don't support ISL so you can only run 802.1Q. That means that there is no need for an encapsulation command because only one encapsulation is supported. If the device had support for ISL then you would also have that command.

Daniel Dib
CCIE #37149

Please rate helpful posts.

[Marvin Rhoads]

As Daniel correctly noted: +5

Just put in your "switchport mode trunk" (preferred) or let the interface autonegotiate trunk/aceess type.

[AI77]

Thanks

[stepnharp]

Thanks for your answer.  Scott

[DaciscoKING]

Thxs Daniel, 

This has been something that has been on my mind for while as i have not found a logcial explanation for this!

Sincerly

DaKING

[RBeugnies]

You can use the "show interface <interface> switchport" command to confirm the operational trunking encapsulation. ISL is not supported on newer devices.