802.1Q vs Trunk on router

On a router I am creating sub-interfaces that are L2 (no ip add and encapsulating dot1q vlan) and I am doing this for multiple vlans. (so every vlan have a sub-interface); however, I being told this is trunk. I do not understand how can we call this a trunk when we are not stating sw mode trunk nor are we using switches. This is a router. Can someone help understand?

Hi,
Probably you are configuring a ROS (router on a stick).
You need to specify the encapsulation on each subinterface.

Hello Shannon

This is indeed a trunk. A trunk is defined as a link between two devices that carries multiple VLANs. These VLANs are separated on the link by a VLAN tag that exists in the header of the frames being sent over that link.

Now the method by which you create a trunk on each device is different. When configuring it on a switch, you do indeed use the switch mode trunk command and all the related commands to send the appropriate VLANs over the link. But for a router, these commands do not exist. The method by which you create a “trunk” is to use subinterfaces. The command that actually makes it a trunk is the encapsulation dot1q command which is followed by the VLAN ID for that particular subinterface. Note the dot1q keyword, which essentially tells the router to use the 802.1Q standard, which defines trunks.

Remember that there are other encapsulation types for subinterfaces of routers, one of which is Frame Relay. In that case, the encapsulation command is encapsulation frame-relay as shown in the following lesson.


In this case, the link is not a trunk, but a set of logical Frame Relay circuits that each correspond to a different DLCI.

I hope this has been helpful!

Laz

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This is exactly what I needed to read. Thank you so much!!