01-23-2008 05:06 PM - edited 03-03-2019 08:24 PM
Hi Experts,
I would like to understand..If a gigabit port is trunk to another switch from Core Switch, and I dun wan to put the command switchport mode trunk,
what is the different ? I have tried not putting it and it is still ok.
Thanks,
01-23-2008 05:23 PM
The port can be in "auto" mode that will cause it to go trunk as necessary.
01-23-2008 08:03 PM
hi,
What is the OS of gig interface switch?
On catos for all ethernet interfaces the default is dynamic auto and for cisco IOS it is dynamic desirable (default for all ethernet interfaces).
The dyanmic auto (in case of cat os) puts the interface in trunk mode if the neighbouring interface is set to trunk or desirable (no auto mode here).
The dynamic desirable mode (in case of NATIVE IOS) puts the interface in trunk mode if the opposite end is set to trunk,desirable OR AUTO mode.
HTH,
regards,
shri :)
01-24-2008 12:11 AM
Hi Cindy,
First you need to check the default status of your interface using "sh interfaces g0/1 switchport" for example, which varies according to the platform, for example the 3550 uses dynamic desirable by default, while the 3560 uses dynamic auto by default.
Check the administrative and operational modes in the output of the command.
As Shri pointed out, you need to take care of the operational combination:
Desirable (start negotiation - active) > The other side can be: Trunk / Desirable / Auto
Auto (waits for negotiation - passive) > The other side can be: Trunk / Desirable.
Rack1SW1#sh interfaces f0/13 switchport
Name: Fa0/13
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: trunk
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: isl
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
BR,
Mohammed Mahmoud.
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide