Trunking mode

[miracle_david@yahoo.com]

Hi gentlemen,

I wish to know when I should set my switchports' modes as TRUNK? Also, switchports connected to my end devices should be set to TRUNK or no?

All the best 

[Leo Laohoo]

Ideally, all uplinks should be set to Trunk.

[miracle_david@yahoo.com]

What does Trunking exactly do?

[marce1000]

 - You usually don't need trunk-ports to end devices. It may confuse them. You only need trunks for connecting your switches on ports carrying more then one vlan.

 M,

[Seb Rupik]

...also trunks for connecting to servers running hypervisors hosting multiple VMs connected to different VLANs.

cheers,

Seb.

[miracle_david@yahoo.com]

Thanks sir for your reply. What do u mean by "end devices may become confuse"?

[Seb Rupik]

Between the workstation OS and the NIC connecting to the interface, it will expect to receive untagged frames. Without additional configuration it will not process 802.1q tagged frames and will silent drop them.

cheers,

Seb.

[Joseph W. Doherty]

It depends on whether the port needs to carry more than two VLANs (or more than one VLAN if you shouldn't, or cannot, use a voice VLAN), or even one VLAN if frames are tagged, or, I believe, VTP requires trunks (or possibly another reason that doesn't come to mind).

Generally, access mode is used for ports connecting to edge devices (like PCs), but as mentioned by Seb, some hosts (like servers), can support different virtual hosts using tagged frames. Otherwise, trunk ports, are most often used for links between switches (and sometimes between switches and routers).

BTW, non-Cisco VLAN switches usually also support multiple VLAN ports but may use a different term than "trunk". They might not support non-tagged frames on such ports and they probably won't support the older Cisco protocol ISL.