Is trunk port necessary when there is only one VLAN configured on a switch?

[Mohamed Fyaz]

Hi All,

I have VLAN 10 created on a layer 2 switch (Switch 1 ).

And I created VLAN 20 on another layer 2 switch (Switch 2).

I understand there should be routing between these 2 VLANs in order for it to communicate.

I connected both this switches to a router on two different ports. (g0/0 and g0/1). and assigned the default gateway. 

Since there is only one VLAN configured on each switch, is it necessary to create a trunk port ? 

Please advise. Because when I tried creating switchport mode access from switch to router, I was not able to reach VLAN 20 from VLAN 10.

Thanks,
Fyaz

[gs.skills · Accepted solution]

Hello,

No it's not required.

You need an ip adress on each router interface within the right subnet (ONE SUBNET/VLAN), the port on the switch must be set to the right vlan too (switchport access vlan X).

The benefits with a trunk link is that it is more flexible: if you want to add a vlan, you only need to add subinterface on the router, the vlan on the switch, set some access ports to this vlan and your done.

Regards, Guillaume

[Mohamed Fyaz]

Hi Guillaume,

Great it helped me !  and thanks for the explanation about the trunk link.

So in the case of multiple vlans on a single switch, we create a trunk port and in the router level, we define the ip address for each vlans in dot1q command? 

I would like to clarify, we are using dot1q to identify different vlans carried out by the trunk link?

Thanks,
Fyaz

[gs.skills]

You create a subinterface on the router for each vlan and set the dot1q tag in hte subinterface configuration.
Your are right, dot1q adds a tag to each frame and use it to identify the vlan it belongs to.
This configuration is often called a Router On A Stick, ROAS, you can find plenty of configuration examples. There is just a little trick about the concept of native vlan
Regards, Guillaume

[Mohamed Fyaz]

okay got it ! Thanks alot Guillaume! :)