Switchport mode trunk question

[cindylee27]

Hi Experts,

I have 2 switches. One is switch 3020 and the other one is switch 3750. The port 17 of switch 3750 is configured as trunking port, as below :

switchport trunk encapsulation dot1q

switchport mode trunk

speed 1000

duplex full

The other port 17 at Switch 3020, is configured as below:

interface fastethernet0/17

switchport access vlan 33

--------------------------------------

I have a server connected to port 15, vlan 31.

There is also virtual interface of vlan 31 at 3750 with hsrp standby ip.

-------------------

The question is.. why I am still able to ping to the server from a user that connected to 3750 since the vlan at the trunking is only 33?

Thanks in advanced.

[lgijssel]

As you have not specified the port at the 3020 to be in access mode (switchport mode access) the default is in operation.

The default is auto-trunking; when a trunk is discovered on a port, a trunk is established.

You can verify this by checking: sh int ../17 switchport.

This will give you the operational trunking mode.

regards,

Leo

[cindylee27]

Thanks Leo..so this trunking will also applied even when the switchport access vlan xxx is configured at the switchport ??

meaning it can take all the vlans numbering across right? ;)

Thanks again..

[lgijssel · Accepted solution]

The setting "switchport access vlan xxx" determines the vlan ID for the port WHEN it is in access mode. To hard-code it in acces mode you need to enter the command "switchport mode access" as well.

This setting widely recommended as a security measure for ports that you do not want to use as trunks. In this way you can prevent that the attachment of a switch allows access to any vlan in the network.

Leo

[cindylee27]

Thanks Leo..

Helpful reply.. :)

Have rated your post..

Regards,

[lgijssel]

Rating posts is always good.

Thanks a lot!!