Could not start DHCPv4 server instance: Address already in use

Question

I am trying to set up an isolated lan using systemd-networkd on a RPi3B+ running Debian GNU/Linux 11 (bullseye) 64b. I followed the recipe here Workaround for a wifi bridge on a Raspberry Pi with proxy arp. The L3 bridge using parprouted is working using the subnetting procedure as expected when I have the wlan0 interface hooked to my home lan. My problem is when I try to enable the DHCP server on the RPi; then networkctl shows the DHCP server could not start because "Address already is use".

● 3: wlan0                      
                     Link File: n/a
                  Network File: /etc/systemd/network/08-wifi.network
                          Type: wlan
                         State: routable (configured)
                          Path: platform-3f300000.mmcnr
                        Driver: brcmfmac
                    HW Address: b8:27:eb:18:6b:5f (Raspberry Pi Foundation)
                           MTU: 1500 (min: 68, max: 1500)
                         QDisc: pfifo_fast
  IPv6 Address Generation Mode: eui64
             WiFi access point: RPiGemini (00:00:00:00:00:00)
          Queue Length (Tx/Rx): 1/1
                       Address: 192.178.4.14
                                fe80::ba27:ebff:fe18:6b5f
             DHCP6 Client DUID: DUID-EN/Vendor:0000ab11db141ed8ce5dd9d00000
           Offered DHCP leases: none

Sep 18 05:12:35 raspberrypi systemd-networkd[174]: wlan0: Link UP
Sep 18 05:12:36 raspberrypi systemd-networkd[174]: wlan0: Link DOWN
Sep 18 05:12:36 raspberrypi systemd-networkd[174]: wlan0: Link UP
Sep 18 05:12:36 raspberrypi systemd-networkd[174]: wlan0: Gained carrier
Sep 18 05:12:36 raspberrypi systemd-networkd[174]: wlan0: Could not start DHCPv4 server instance: Address already in use
Sep 18 05:12:38 raspberrypi systemd-networkd[174]: wlan0: Gained IPv6LL

Would someone suggest how to proceed for further debug ? I am not clear on were the address conflict could be. Thank you for your time.

score 1 · Accepted Answer · answered Sep 18 '22 at 16:09

1

Address already is use

Means something is using the DHCP server port, presumably a DHCP server. Check with:

lsof -i UDP:67

answered Sep 18 '22 at 16:09

goldilocks

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Thank you for the response. I was thinking about a IP address conflict. Now I see it was the dhcp-helper.service. It seems I mixed up two different thing since I don't actually need the dhcp-helper.service. I disable it and now everything is working. – JeffD Sep 18 '22 at 17:09

Could not start DHCPv4 server instance: Address already in use

1 Answers1