this post was submitted on 07 Mar 2025
32 points (94.4% liked)

Selfhosted

46672 readers
874 users here now

A place to share alternatives to popular online services that can be self-hosted without giving up privacy or locking you into a service you don't control.

Rules:

  1. Be civil: we're here to support and learn from one another. Insults won't be tolerated. Flame wars are frowned upon.

  2. No spam posting.

  3. Posts have to be centered around self-hosting. There are other communities for discussing hardware or home computing. If it's not obvious why your post topic revolves around selfhosting, please include details to make it clear.

  4. Don't duplicate the full text of your blog or github here. Just post the link for folks to click.

  5. Submission headline should match the article title (don’t cherry-pick information from the title to fit your agenda).

  6. No trolling.

Resources:

Any issues on the community? Report it using the report flag.

Questions? DM the mods!

founded 2 years ago
MODERATORS
ruud@lemmy.world
CannaVet@lemmy.world
Loki@lemmy.world
HybridSarcasm@lemmy.world
devve@lemmy.world
HybridSarcasm@lemmy.hybridsarcasm.xyz
32
How to get a unique MAC/DHCP IP for a Docker/Podman container without MACVLAN? (lemmy.blahaj.zone)
submitted 3 months ago by glizzyguzzler@lemmy.blahaj.zone to c/selfhosted@lemmy.world
13 comments fedilink hide all child comments
 

I have a bridge device set up with systemd, br0, that replaces my primary ethernet eth0. With the br0 bridge device, Incus is able to create containers/VMs that have unique MAC addresses that are then assigned IP addresses by my DHCP server. (sudo incus profile device add <profileName> eth0 nic nictype=bridged parent=br0) Additionally, the containers/VMs can directly contact the host, unlike with MACVLAN.

With Docker, I can't see a way to get the same feature-set with their options. I have MACVLAN working, but it is even shoddier than the Incus implementation as it can't do DHCP without a poorly-maintained plugin. And the host cannot contact the container due to the MACVLAN method (precludes running a container like a DNS server that the host server would want to rely on).

Is there a way I've missed with the bridge driver to specify a specific parent device? Can I make another bridge device off of br0 and bind to that one host-like? Searching really fell apart when I got to this point.

Also, if someone knows how to match Incus' networking capability with Podman, I would love to hear that. I'm eyeing trying to move to Podman Quadlets (with Debian 13) after I've got myself well-versed with Docker (and its vast support infrastructure to learn from).

Hoping someone has solved this and wants to share their powers. I can always put a Docker/podman inside of an Incus container, but I'd like to avoid onioning if possible.

you are viewing a single comment's thread
view the rest of the comments
[–] litchralee@sh.itjust.works 4 points 3 months ago (7 children)

I want to make sure I've understood your initial configuration correctly, as well as what you've tried.

In the original setup, you have eth0 as the interface to the rest of your network, and eth0 obtains a DHCP-assigned address from the DHCP server. Against eth0, you created a bridge interface br0, and your host also obtains a DHCP-assigned address in br0. Then in Incus, you created a Macvlan network against br0, such that each containers against this network will be assigned a random MAC, and all the container Ethernet frames will be bridged to br0, which in-turn bridges to eth0. In this way, all containers can each receive a DHCP-assigned address. Also, each container can send traffic to the br0 IP address, to access services running on the host. Do I have that right?

For your Docker attempt, it looks like you created a Docker network using the Macvlan driver, but it wasn't clear to me if the parent interface here was eth0 or br0, if you still have br0. When you say "I have MACVLAN working", can you describe which aspect is working? Unique MAC assignment? Bridged traffic to/from the containers or the network?

I'm not very familiar with Incus, but I'm entirely in the dark about this shoddy plugin you mentioned for DHCP and Macvlan to work. So far as I'm aware, modern Docker Engine uses the CNI plugins when creating networks, so the "-d macvlan" parameter specifies which CNI plugin will load. Since this would all be at Layer 2, I don't see why a plugin is needed to support DHCP -- v4 or v6? -- traffic.

And the host cannot contact the container due to the MACVLAN method

Correct, but this is remedied by what's to follow...

Can I make another bridge device off of br0 and bind to that one host-like?

Yes, this post seems to do exactly that: https://kcore.org/2020/08/18/macvlan-host-access/

I can always put a Docker/podman inside of an Incus container, but I'd like to avoid onioning if possible.

I think you're right to avoid multiple container management tools, if simply because it's generally unnecessary. Although it kinda looks like Incus is more akin to Proxmox, in that it supports managing VMs and containers, whereas Podman and Docker only manage containers, which is further still distinct from the container runtime (eg CRI-O, containerd, Docker Engine (which uses containerd under the hood)).

[–] glizzyguzzler@lemmy.blahaj.zone 2 points 3 months ago (6 children)

Thanks for taking the time to reply!

The host setup has eth0 as the physical interface to the rest of the network, with br0 replacing it completely. br0 has the same MAC as the eth0 interface and eth0 just forwards to br0 which then does the bridging internally. br0 being a bridge means that incus is able to split it off without MACVLAN but rather its nic device in bridge mode which "Uses an existing bridge on the host (br0) and creates a virtual device pair to connect the host bridge to the instance." That results in a network interface that has its own MAC and is assigned a local IP by the DHCP server on the network while also being able to talk to the host.

Incus accomplishes the same goal as Proxmox (Proxmox has similar bridge network devices for its containers/VMs) just without Incus needing to be your OS/distro like Proxmox does, it's just a package.

As for the Docker, the parent interface is br0 which has supplanted eth0. MACVLAN is working as it is intended to in Docker, as far as I can tell. The container has a networking device with its own MAC address, and after supplying the MACVLAN network device with my network's subnet and gateway and static IP address in the Docker compose file it works as expected. If I don't supply a static IP in the Docker compose file, Docker just assigns it the first IP in the given subnet - no DHCP interaction. This docker-net-dhcp plugin (I linked to the issue about it not working on the latest version of Docker anymore) was made to give Docker network devices the ability to use DHCP to get an IP address, but it's clearly not something to rely on.

If I'm missing something about MACVLAN that makes DHCP work for Docker, let me know! Hardcoding an IP into a docker-compose file adds an extra step to remember compared to everything else being configured on the centralized DHCP server - hence the shoddy implementation claim for Docker.

Thanks for the link to using another MACVLAN and routing around the host<-/->container connection issue inherent to MACVLAN. I'll keep it in mind as an alternate to Incus container around another container! I do wish there could be something like Incus' hassle-free solution for Docker or Podman.

[–] MangoPenguin@lemmy.blahaj.zone 2 points 3 months ago (2 children)

What about using the default docker bridge networking instead of macvlan? You can access docker containers from the host, they can talk to each other if on the same bridge network, and there's nothing hardcoded into the docker compose files.

[–] glizzyguzzler@lemmy.blahaj.zone 1 points 3 months ago (1 children)

With the default Docker bridge networking the container won’t have a unique IP/MAC address on the local network, as far as I am aware. Communication with external clients will have to contact the host server’s IP at the port the container is tied to in order to interact. If there’s a way to specify a specific parent interface, let me know!

[–] MangoPenguin@lemmy.blahaj.zone 1 points 3 months ago

Thats correct but that is fine for the majority of setups.

load more comments (3 replies)
load more comments (3 replies)