this post was submitted on 05 Apr 2026
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Docker networking help (vlans) (programming.dev)
submitted 16 hours ago* (last edited 16 hours ago) by zo0@programming.dev to c/selfhosted@lemmy.world
10 comments fedilink hide all child comments
 

Hi folks, hope your weekend is going well.

So I have put myself into a situation. I have a home server with docker installed running fine so far. In my home network I have multiple networks for different purposes. The whole network stack looks like this OPNSense

Switch

Ubuntu Server

The server is connected to a switch port with pvid 100, and runs on vlan0.100 Now my goal is to move some docker containers to other vlans. To accomplish that I have set vlan0.101 and vlan0.102 on my server as interfaces with their own IP and default gateway on that subnet (e.g. 192.168.101.10) Next step I set up macvlans for my docker containers Then I set the port to also allow tagged traffic, but kept it on pvid 100. Now on my OPNSense I changed the host ip of my server from 192.168.100.10 to include all 3 IPs so homeserver 192.168.100.10, 192.168.101.10, 192.168.102.10

This setup seems to work fine for internal network, however no services are reachable from the outside (internet) anymore.

My first question is: Am I thinking correctly about this? Or is this over-engineered bs at this point and there is a better way to put docker containers on different subnets.

Second question is: Any ideas what's breaking the internet access?

Thanks for the help in advance :D

EDIT: i have not changed the vlan of any container yet

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[–] Decronym@lemmy.decronym.xyz 1 points 12 hours ago* (last edited 8 hours ago)

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
DHCP Dynamic Host Configuration Protocol, automates assignment of IPs when connecting to a network
DNS Domain Name Service/System
IP Internet Protocol
LXC Linux Containers

4 acronyms in this thread; the most compressed thread commented on today has 7 acronyms.

[Thread #213 for this comm, first seen 5th Apr 2026, 13:20] [FAQ] [Full list] [Contact] [Source code]

[–] probable_possum@leminal.space 2 points 14 hours ago* (last edited 14 hours ago) (2 children)

I don't think I know the reason for the issue you've described. I don't have enough information for that.

First thing would be: Is the routing and firewalling OK? Later: DNS. Even later: services reachable?

The Opnsense instance has configured multiple VLANs and zones too? With one server interface in each? The packets between the vlans take a path via the router?

I tried to give my server multiple interfaces on different VLANs once, but ran into problems with that approach. I then added one bridge interface per VLAN to the server and gave it just one IP on one vlan. That way the server isn't tempted to route things itself or deliver packets on a wrong interface. An entire class of possible errors was removed that way. Docker containers and VMs still can have IPs in their respective VLANs/ nets.

It is worth noting that docker firewalling and ufw don't play well together, which could be the reason for unreachable services. Moving the docker host into a LXC abstracts the issue away. Incus can run OCI containers itself and may be an alternative to docker (but not docker compose).

I can't say anything about over-engeering. It is a hobby after all and you decide what is important and how much complexity you need. :)

[–] irmadlad@lemmy.world 1 points 9 hours ago

It is worth noting that docker firewalling and ufw don’t play well together

This. It took me a little fiddling to get it right

[–] zo0@programming.dev 1 points 14 hours ago (2 children)

Answer to your first question, he dockers successfully resolve and access internet

  1. Yes the OPNSense is the primary router and dhcp provider so all the subnets and vlans are defined and working with physical devices

I actually was having the same issue with the routing of server. How did you setup your bridge exactly? Do you mind sharing your netplan?

[–] probable_possum@leminal.space 1 points 10 hours ago* (last edited 9 hours ago)

Netplan config? Sure:

network:
  ethernets:
    enp35s0:
      dhcp4: false
    enp36s0:
      dhcp4: false
  vlans:
    enp35s0.100:
      id: 100
      link: enp35s0
      dhcp4: false
    enp35s0.101:
      id: 101
      link: enp35s0
      dhcp4: false
  bridges:
     br0:
	   # untagged
       interfaces: [enp35s0]
       dhcp4: false
     br0.100:
	   # vlan 100
       interfaces: [enp35s0.100]
       dhcp4: false
     br0.101:
	   #vlan 101
       interfaces: [enp35s0.101]
       dhcp4: true
  version: 2

I'm not sure if the version-property is still required. The only interface with an IP is br0.101. Opnsense provides DHCP (v4).

You can attach multiple ethernet-devices to a bridge (which I did not):

      br0.100:
        interfaces:
          - enp35s0.100
          - two
	        - three

I'm not sure if you can attach the docker bridge via netplan - it has to exist at boot time, I think. My docker containers run inside a VM (kvm) with one interface, which sits in one of the VLANs. The VM's interface is a bridge device (br0.100). The VM ethernet device is attached to the bridge, it receives its IP from the router and behaves like a real server.

[–] surewhynotlem@lemmy.world 1 points 12 hours ago (1 children)

Bridge? There's your problem I think. Bridge doesn't allow ingress to individual IPs. In bridge, you tell each container what port it listens on, then access it from the IP of the host.

User defined bridges act differently from the default one as well. May not be relevant to your issue, but https://docs.docker.com/engine/network/drivers/bridge/#differences-between-user-defined-bridges-and-the-default-bridge

[–] zo0@programming.dev 1 points 12 hours ago (1 children)

I mean at the moment I don't have any bridges setup (other than the dockers own bridge) I thought maybe I could solve my issue with bridging

[–] surewhynotlem@lemmy.world 1 points 8 hours ago

Oh, hmm. How are you telling which service to be on which IP then? Could you safely post your compose file?

[–] frongt@lemmy.zip 1 points 13 hours ago (1 children)

If LAN works but WAN fails, it's probably a gateway or routing issue. Does your router know it's the gateway for those subnets? Do the clients have the gateway configured? Are there routes for packets to find their way out, and back in from the gateway to the client?

[–] zo0@programming.dev 1 points 12 hours ago

That is my gut feeling too, but as I mentioned in another comment all physical devices work fine in their respective subnet. This is happening before I move the containers to a new subnet, and before these changes everything was working fine.