What does a non-configured port default to?

[rebeccaemerson]

I have two 2950c-24 Switches connected together via a crossover cable on port 24 on both switches.

On one switch someone has configured Port 24 with trunking but on the other switch, there is no configuration on port 24 at all. With this type of configuration, I would have thought that you wouldn't be able to communicate between the two switches ... but they are talking ... and they seem to be talking happily. How is this? Does a non-configured port default to something - which in turn makes this communication possible?

I have checked the status of port 24 on both switches and they say they are connected and packets are going between them.

If anyone has any answers then that would be greatly appreciated.

Thanks.

[ankurbhasin · Accepted solution]

Hi Rebeccaemerson,

Yes it will work and work perfectly.

The reason is the switch 2950 default behaviour is "dynamic desirable" for all the ports so if one switch is configured as trunk the other side port will automatically form a trunk and you can see it with command "sh int fa0/24 switchport" and you will see operational mode as trunk.

By default all the ports are in dynamic desirable and are in vlan 1 so if the other side is not configured as anthing it will work on vlan 1 access port only but if other side is configured as trunk it will also default work in trunking mode because of default interface behaviour.

Check this link for default interface behaviour

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12119ea1/2950scg/swvlan.htm#1116255

HTH

Ankur

[ankurbhasin]

Hi Rebeccaemerson,

Yes it will work and work perfectly.

The reason is the switch 2950 default behaviour is "dynamic desirable" for all the ports so if one switch is configured as trunk the other side port will automatically form a trunk and you can see it with command "sh int fa0/24 switchport" and you will see operational mode as trunk.

By default all the ports are in dynamic desirable and are in vlan 1 so if the other side is not configured as anthing it will work on vlan 1 access port only but if other side is configured as trunk it will also default work in trunking mode because of default interface behaviour.

Check this link for default interface behaviour

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12119ea1/2950scg/swvlan.htm#1116255

HTH

Ankur