DSA switch with VLAN tagging

I'm using a Belkin RT3200 as AP and as a switch.
Using ports 1(tagged) and 3 (untagged), two hosts on a different subnet than openwrt are able to communicate transparently.
Now, I would like to understand more about these bridges, but I couldn't find any CLI tool to monitor what's actually happening.
ip link doesn't show anything dsa-related and (obviously) swconfig list produces no output.

Any hints?

I haven't seen any really good explainers that describe the theory of operation, but there is the DSA mini tutorial which goes through DSA in practice as well as a few blurbs about why things are setup in certain ways.

If that doesn't help you understand what's happening and why, can you elaborate on what it is you're trying to learn so we can try to answer it more directly? And, while you're at it, please let us know your familiarity with either swconfig or VLANs in general (in switches) so that we can don't over-explain or under-explain the concepts.



you could start with
bridge -compressvlans vlan
bridge fdb

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DSA itself is what I have come to understand a protocol or system to communicate switch port setup data between cascading switches in a network. But how that is done in real life I have never seen. And does other switch manufacturers call that function anything other that DSA.

The thing was that Linux dropped (or was going to) the support for swconfig so we had to make the change to DSA.

The term bridge in the config file if I remember an old mail conversation from the 2019-2021 dev times was not really cut in stone, that was more a result of a long conversation.

Bridge as we use it is more like what switch manufacturers sometimes call “port isolation”, but most of the time the switches we use put all ports inside the same bridge.
The bridge collects a group of ports that are allowed to send data between them. Under that bridge called bridge (with a device name) you can define specific grain size filter on the legs (ports) that let the grains with correct size drop down (that filter is VLAN).
But the data packages can’t move between different bridges.

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On top of this if we look at the realtek (real full size)switch project we have, the definition switch has also been introduced on top of bridge in the network config files.
But here the switch defines the ports and bridge only give them a name and a mac.
Why this happend I have no real clue!?

But in the end this question is right, we have no system explanation wiki of this we call DSA and we don’t have an options table. The only thing we have is the config examples wiki that was created with the release of 21.02 to handle the “what is this” forum storm.

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First, can you take a look at my post on the following topic:

Second, to see what's the actual configuration applied to the bridge with vlan filtering, you can install the ip-bridge package and use the commands NPeca75 wrote.

@flygarn12 swconfig was never in the mainline linux kernel. When a discussion about upstreaming it began, Marvell (a company making switch chips) already had their DSA code in the mainline kernel so kernel developers decided to adopt the DSA code to support all other switches instead of adding a completely new (swconfig) API to the kernel. DSA supports 99% of what swconfig can do while providing much greater flexibility.

DSA downsides are:

  • if you have multiple CPU connected ports - like for example on TL-WR1043ND, it was not possible to use them - but that changed recently - see commit f1c9afd801380a05a91d979b475c76cc0a67caae on MT7621 SoC for an example on how to achieve that

DSA upsides are:

  • combine ports from multiple DSA switches, native ethernet, wifi and virtual interfaces and even L2 VPNs into one bridge with or without vlan filtering
  • remove ports on a DSA switch from the bridge and they will become independent
  • hardcode MAC addresses to specific ports in the FDB
  • probably implement 802.1x authentication on individual ports
  • set "isolated" on ports so they can't communicate between each other

We only need this excellent information you have in the wiki so we don’t need to have this question over and over again spread out in the forum.

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Thanks, that's exactly what was needed!

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i am glad :slight_smile:

would you please mark topic as [solved] and proper answer as solution ?

how to mark topic solved

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