DD-WRT :: View topic - [SOLVED]The difference between a BRIDGE and a VLAN in DD-WRT (2024)

The only reason I ask is because the NVRAM settings for each are almost identical, and given bridges are created 'in software' the same as VLANs, I can't really see how they are functionally different.

Why do I think this an important question?
If for no other reason, for spanning tree.
I don't want to inadvertently create a 'spanning tree loop' internal to the device itself - in memory. I can foresee this being well within the realm of possibilities.

Also, why would we config an IP address on the BRIDGE instead of the VLAN?
When would the VLAN need an IP address configured?

Example NVRAM settings attached.

Last edited by ddux on Tue Apr 23, 2024 2:32; edited 1 time in total

Right, so perhaps the best way to think of a bridge is like a virtual switch (in memory) that is used to group two or more interfaces together whereby ingress frames received on one interface are switched at layer 2 to another interface based on the switch mac address table and sent out as egress frames.

I think that it is very important when discussing bridges and VLANs and VLAN (802.1q) tags to always keep in mind the direction of a given layer 2 frame - whether it is INGRESS (Rx) or EGRESS (Tx).

I would like to see a more detailed tutorial on bridge and VLAN configuration which explains in detail the flow of traffic between internal ports which specifically mentions INGRESS (Rx) and EGRESS (Tx) such that the path of a given layer 2 ethernet frame is unambiguously described and can be (at least mentally) traced from interface to interface (including external and interface), all the way from the first frame received on INGRESS (Rx) on an external port from an external device, through to the forwarding of said frame out another (or the same) external interface as an ENGRESS (Tx) frame to an external device, including wireless interfaces.

One thing I am still not 100% clear on is whether the 'CPU Port' behaves like an 802.1q VLAN tagged interface connected to a 'router on a stick', to use a common networking term. I believe it does based on all the diagrams I have see from other more knowledgeable posters, but confirmation from a DD-WRT developer would be great.

In any case, thanks so much for your input.

A bridge is a bridge and is mainly used to bridge multiple interfaces.
And a VLAN interface is a VLAN interface.

If you don't have several interfaces to bridge, you can also do without the bridge and assign an address directly to the VLAN interface.

I generally use bridges in my example because bridges can be extended with other interfaces and because you can use the same firewall rules everywhere.

Routers
Marvell OCTEON TX2 - QHora-322 - OpenWrt 23.05.3 - Gateway
Qualcomm IPQ8065 - R7800 - DD-WRT - WAP

Yes it does. That is why you see the VLANx interfaces in the router

Thanks for your input, but I wanted to address this.
Clearly I upset you. Sorry, that was not my intent. You've been very helpful with the other stuff and I am grateful.

I obviously did not explain myself properly in my original question.
I am well aware of the difference between bridges and VLANs as I have been working in networking for over 2 decades. I can describe hubs, repeaters, bridges, transparent bridges, etc.

What I was not certain about was how the terms were being used in this context. Over my career I have come across many people and places who use these terms loosely and often incorrectly in a technical sense. My question was one of clarification in the DD-WRT context, and trying to understand how the concept of VLANs and bridges have been functionally implemented in the DD-WRT source.

Also, please do not misquote me - I specifically did not use the term 'VLAN interface' for a reason. A VLAN and a VLAN interface are not the same thing

Finally, definitions logically cannot contain the thing being defined.

That said, thanks again for all your help and advice. It is appreciated.