Documentation clarification with regards to specifying multiple MAC addresses per single container.

[arizvisa]

I wasn't originally sure if this'd be a podman question or not, since the majority of podman-network-create(1)'s options are implemented by the network backend (netavark), but the referenced documentation is in podman and netavark's "discussions" seem a little shallower than here.

So... to start out (in case my whole process is busted), I have a container that needs its address to be managed externally. This implies that I can use the macvlan driver and proxy dhcp requests from the network that the container will be deployed on. The one issue with this is that the hwaddr for the container's interface is randomly generated, but this can be remedied using the --mac-address parameter when running the container. This is a little clumsy, but it works fine.

However, I have another container that needs to be bound to multiple network interfaces and (similarly) the only requirement is that its mac-address is predictable/settable on each of those interfaces so that the dhcp on each of its networks can manage it. The software also cannot be run concurrently in separate containers, due to the way it maintains its state.

Anyways, the last line in the following snippet from the documentation (other lines included for context) is the one in question.

podman/docs/source/markdown/options/mac-address.md

Lines 5 to 15 in 0904c19

	#### **--mac-address**=*address*
	<<Container|Pod>> network interface MAC address (e.g. 92:d0:c6:0a:29:33)
	This option can only be used if the <<container|pod>> is joined to only a single network - i.e., **--network=_network-name_** is used at most once -
	and if the <<container|pod>> is not joining another container's network namespace via **--network=container:_id_**.
	Remember that the MAC address in an Ethernet network must be unique.
	The IPv6 link-local address is based on the device's MAC address
	according to RFC4862.
	To specify multiple static MAC addresses per <<container|pod>>, set multiple networks using the **--network** option with a static MAC address specified for each using the `mac` mode for that option.

I tried fiddling around with podman-network-create(1), and couldn't for the life of me figure out what options to specify. Netavark doesn't seem to be documented that well, so I went spelunking through the source code to figure out what options the "macvlan" driver has. Although I'm terrible at rustlang, it reads as if there are no options other than "mtu", "parent", "vrf", "bclim", "metric", and "no_default_route" (https://github.com/containers/netavark/blob/29ad799acf1195726a8e040f965ff93041443a99/src/network/vlan.rs#L18-L20). This prevents me from specifying the hwaddr each of the ethernet interaces within the container.

I re-read the documentation, and then realized that maybe I could specify the mac address as an option to the network via podman-container-run, but I get errno 99 from what appears to be netavark.

# podman network inspect systemd-interface-private
[
     {
          "name": "systemd-interface-private",
          "id": "b923ad581fed228038d3c4082e29f8b75b3d7ac731c55ee01879e88c40a28511",
          "driver": "macvlan",
          "network_interface": "en-private",
          "created": "2023-11-03T03:08:13.238867541Z",
          "ipv6_enabled": false,
          "internal": false,
          "dns_enabled": false,
          "ipam_options": {
               "driver": "dhcp"
          }
     }
]

$ /usr/bin/podman run --rm -it --network=systemd-interface-private:mac=21:21:21:32:32:32 quay.io/fedora/fedora:latest /bin/sh -i
Error: netavark: create macvlan interface: Netlink error: Cannot assign requested address (os error 99)

Anyways, I'm pretty sure that the referenced documentation is only referring to the "bridge" driver with regards to the "mac" option, and that none of the other drivers are relevant. Is that safe to assume? And if that's the case, is there some other way to have a container request dhcp leases for each of its associated networks with a non-random mac address?

(edited)

Apparently this already works as per containers/netavark#728, and was closed as "not planned". But I'm still not sure what I'm missing and how to modify my container/network units to accomplish this.

[Luap99]

--network=systemd-interface-private:mac=21:21:21:32:32:32 is the correct syntax, the reason it fails because you specify an invalid mac address.
The 7 and 8 bit have a special meaning, you cannot ever set the 8 bit to 1 because that means it is a multicast mac, see https://en.wikipedia.org/wiki/MAC_address#Address_details

So in short the the second hex digit should never be odd. If you use 20:21:21:32:32:32 it will work.

[arizvisa]

Lol. That is so enraging that I wasted so much time and it was my test case that I was using for experimenting with options which was wrong. :)

Thanks soo much, @Luap99. I updated the container units that I was using, appended the "mac" option that I was originally using to their network units, and everything works perfectly. Mad appreciate your super quick response.