Is DHCP/DNS detection a windows plugin only?

[kan-ibal]

Is it Windows only plugin?
I'm looking forward for such solution regarding captive portals issue and I am wandering why is this not working in any linux system I test.

[jedisct1]

It works on MacOS for sure and should work on Linux as well.

Make sure that the server is running as root (user_name should not be set).

Do you see a message that says "Starting a DHCP/DNS detector for IPv4" ?

[kan-ibal]

Do you see a message that says "Starting a DHCP/DNS detector for IPv4" ?

Yes, I can see in log:
[NOTICE] Starting a DHCP/DNS detector for IPv4

but if I want to resolve a test.domain I redirected to DHCP resolver I'm getting:
[INFO] DHCP didn't provide any DNS server to forward [test.domain]

[lifenjoiner]

Bad luck. Test some other routers and client devices combinations. The Ubuntu GitHub CI test works.
Maybe the router has some limits/restrictions, or your OS has other DHCP clients and doesn't allow multiple clients sharing the same communication ports?

[lifenjoiner]

Wait more than 90s since "Starting a DHCP/DNS detector", then dig.

[kan-ibal]

[INFO] No response from the DHCP server while resolving [openwrt.home]: read udp4 0.0.0.0:68: i/o timeout
[INFO] DHCP didn't provide any DNS server to forward [openwrt.home]
[INFO] No response from the DHCP server while resolving [openwrt.home]: read udp4 0.0.0.0:68: i/o timeout
[INFO] DHCP didn't provide any DNS server to forward [openwrt.home]

[lifenjoiner]

Can you test if this CLI demo gets the DNS on your Linux?
Ubuntu amd64: https://github.com/lifenjoiner/dhcpdns/actions/runs/18613333853

./cli -n 10

[kan-ibal]

2025/10/18 23:31:38 Targeting: 8.8.8.8:80
2025/10/18 23:31:40 Constancy: 1
2025/10/18 23:31:40 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:31:40 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:31:40 Active local IP: 192.168.1.x
2025/10/18 23:31:40 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:31:40 Constancy: 1
2025/10/18 23:31:40 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:31:40 Active local IP: 
2025/10/18 23:31:50 Targeting: 8.8.8.8:80
2025/10/18 23:31:52 Constancy: 2
2025/10/18 23:31:52 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:31:52 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:31:52 Active local IP: 192.168.1.x
2025/10/18 23:31:52 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:31:52 Constancy: 2
2025/10/18 23:31:52 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:31:52 Active local IP: 
2025/10/18 23:32:02 Targeting: 8.8.8.8:80
2025/10/18 23:32:04 Constancy: 3
2025/10/18 23:32:04 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:32:04 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:32:04 Active local IP: 192.168.1.x
2025/10/18 23:32:04 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:32:04 Constancy: 3
2025/10/18 23:32:04 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:32:04 Active local IP: 
2025/10/18 23:32:14 Targeting: 8.8.8.8:80
2025/10/18 23:32:16 Constancy: 4
2025/10/18 23:32:16 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:32:16 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:32:16 Active local IP: 192.168.1.x
2025/10/18 23:32:16 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:32:16 Constancy: 4
2025/10/18 23:32:16 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:32:16 Active local IP: 
2025/10/18 23:32:26 Targeting: 8.8.8.8:80
2025/10/18 23:32:28 Constancy: 5
2025/10/18 23:32:28 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:32:28 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:32:28 Active local IP: 192.168.1.x
2025/10/18 23:32:28 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:32:28 Constancy: 5
2025/10/18 23:32:28 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:32:28 Active local IP: 
2025/10/18 23:32:38 Targeting: 8.8.8.8:80
2025/10/18 23:32:40 Constancy: 6
2025/10/18 23:32:40 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:32:40 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:32:40 Active local IP: 192.168.1.x
2025/10/18 23:32:40 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:32:40 Constancy: 6
2025/10/18 23:32:40 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:32:40 Active local IP: 
2025/10/18 23:32:50 Targeting: 8.8.8.8:80
2025/10/18 23:32:52 Constancy: 7
2025/10/18 23:32:52 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:32:52 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:32:52 Active local IP: 192.168.1.x
2025/10/18 23:32:52 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:32:52 Constancy: 7
2025/10/18 23:32:52 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:32:52 Active local IP: 
2025/10/18 23:33:02 Targeting: 8.8.8.8:80
2025/10/18 23:33:04 Constancy: 8
2025/10/18 23:33:04 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:33:04 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:33:04 Active local IP: 192.168.1.x
2025/10/18 23:33:04 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:33:04 Constancy: 8
2025/10/18 23:33:04 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:33:04 Active local IP: 
2025/10/18 23:33:14 Targeting: 8.8.8.8:80
2025/10/18 23:33:16 Constancy: 9
2025/10/18 23:33:16 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:33:16 Maybe DHCP temporarily failed, keep the last results
2025/10/18 23:33:16 Active local IP: 192.168.1.x
2025/10/18 23:33:16 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:33:16 Constancy: 9
2025/10/18 23:33:16 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:33:16 Active local IP: 
2025/10/18 23:33:26 Targeting: 8.8.8.8:80
2025/10/18 23:33:28 Constancy: 10
2025/10/18 23:33:28 Error: read udp4 255.255.255.255:68: i/o timeout
2025/10/18 23:33:28 Seems can't get DHCP DNS
2025/10/18 23:33:28 Targeting: [2001:4860:4860::8888]:80
2025/10/18 23:33:28 Constancy: 10
2025/10/18 23:33:28 Error: dial udp [2001:4860:4860::8888]:80: connect: network is unreachable
2025/10/18 23:33:28 Active local IP: 
2025/10/18 23:33:28 v4 got: 0
2025/10/18 23:33:28 v6 got: 0

.x sanitizing, IP4 was correct, IP6 is disabled on this workstation

I do not know is this matter but:
dns service at 8.8.8.8 is reachable and resolvable
8.8.8.8:80 via browser is unrechable
8.8.8.8 -> dns.google via browser is reachable
dns addresses provided by router at the moment: 127.0.0.1,192.168.1.1,1.1.1.1,9.9.9.9

[kan-ibal]

I have tested cli on Ubuntu Touch (24.04/noble/arm64):

2025/10/19 10:56:59 Targeting: 8.8.8.8:80
2025/10/19 10:57:00 Constancy: 1
2025/10/19 10:57:00 Error: DHCPv4 TID not match
2025/10/19 10:57:00 Maybe DHCP temporarily failed, keep the last results
2025/10/19 10:57:00 Active local IP: 10.2.0.2
2025/10/19 10:57:00 Targeting: [2001:4860:4860::8888]:80
2025/10/19 10:57:00 Constancy: 1
2025/10/19 10:57:00 Error: no DNS found
2025/10/19 10:57:00 Maybe DHCP temporarily failed, keep the last results
2025/10/19 10:57:00 Active local IP: xxx.....
....
2025/10/19 10:59:16 Constancy: 10
2025/10/19 10:59:16 Error: no DNS found
2025/10/19 10:59:16 Seems can't get DHCP DNS

Active local IP: 10.2.0.2 comes from Wireguard VPN instead of local wifi network(192.x.x.x).

without Wireguard VPN:

2025/10/19 11:24:35 Targeting: 8.8.8.8:80
2025/10/19 11:24:35 Constancy: 1
2025/10/19 11:24:35 Active local IP: 192.168.1.x
2025/10/19 11:24:35 DHCP DNS: 127.0.0.1
2025/10/19 11:24:35 DHCP DNS: 192.168.1.1
2025/10/19 11:24:35 DHCP DNS: 1.1.1.1
2025/10/19 11:24:35 DHCP DNS: 9.9.9.9
2025/10/19 11:24:35 Targeting: [2001:4860:4860::8888]:80
2025/10/19 11:24:35 Constancy: 1