[systemd-devel] Bridging a wifi access point?

[Hadmut Danisch]

Hi,

a technical question:


I'd like to build a router on a machine with four ethernet and one wlan 
adapter,  using Ubuntu 24.04 server, coming with 255.4-1ubuntu8.6.  I 
need to build a bridge with two of the ethernets and the wlan as an 
accesspoint, making use of as much default software as possible, i.e.  
systemd, networkd, netplan.


Problem:

It's easy to configure the wlan adapter as a client and put it in a 
bridge, but not as an access point.


First attempt, straight forward, /etc/netplan/60-bridge-lan.yaml


network:
   version: 2
   renderer: networkd
   
   ethernets:
     enp4s0:
       dhcp4: no
     enp5s0:
       dhcp4: no
       
   wifis:
     wlp1s0:
       dhcp4: no
       access-points:
         "hurra":
            mode:  ap
            password: something
            
       
   bridges:
     lan:
       dhcp4: no
       addresses:
         - "192.168.122.1/24"
         -"fdfc:1234:5678:1234::1/24"
       interfaces:
         - enp4s0
         - enp5s0
         - wlp1s0


doesn't work:

ERROR: wlp1s0: hurra: networkd does not support this wifi mode






Second attempt, doing as many websites propose, running the wlan with hostapd and using it as a regular ethernet, i.e. removing the wifis section and using instead

   ethernets:
     enp4s0:
       dhcp4: no
     enp5s0:
       dhcp4: no
     wlp1s0:
       dhcp4: no

doesn't work either. Error message

2025-04-11T14:11:29.023613+00:00 mini20 systemd-networkd[1281]: wlp1s0:
Failed to set master interface: Device does not allow enslaving to a
bridge. Operation not supported


which is clearly wrong, since a manual

brctl addif lan wlp1s0

works properly



Third attempt, not configuring the wifi with netplan at all, just listing it as a bridge interface, results in

# networkctl
IDX LINK   TYPE     OPERATIONAL SETUP
   1 lo     loopback carrier     unmanaged
   2 enp3s0 ether    routable    configured
   3 enp4s0 ether    enslaved    configured
   4 enp5s0 ether    no-carrier  configured
   5 enp6s0 ether    off         unmanaged
   6 wlp1s0 wlan     degraded    unmanaged
   7 lan    bridge   routable    configured


man pages  systemd.netdev and systemd.network don't help either.






So my question is:


What is the correct and supposed way to build a bridge interface with ethernets and a wifi access point with systemd and networkd?




Thank you and best regards
Hadmut



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