/etc/resolv.conf does not use DNS servers from DHCP.

[IguanaBob]

I noticed while trying to improve network documentation that /etc/resolv.conf is not populated by the DNS servers advertised by DHCP.

View that the DHCP lease does have the DNS server info:

cat /useremain/home/rinkhals/dhcp.lease
DHCP-Lease received or renewed
Interface: wlan0
IP-Adresse: 192.168.21.21
Subnetzmaske: 255.255.255.0
Gateway: 192.168.21.1
DNS-Server: 192.168.21.1 192.168.21.1
NTP-Server: 192.168.21.1 192.168.21.1

But it is not used by /etc/resolv.conf

# wlan0
nameserver 192.168.21.1 # wlan0
nameserver 192.168.21.1 # wlan0

Nor is it used on a dig:

# nslookup google.com
Server:		1.1.1.1
Address:	1.1.1.1:53

Non-authoritative answer:
Name:	google.com
Address: 142.251.116.102
Name:	google.com
Address: 142.251.116.100
Name:	google.com
Address: 142.251.116.101
Name:	google.com
Address: 142.251.116.138
Name:	google.com
Address: 142.251.116.139
Name:	google.com
Address: 142.251.116.113

Likely this is a bug in the stock firmware, but maybe Rinkhals can fix it. I may be able to fix it, but putting the issue here in case I don't have time to get to it.

Thanks again.

[jbatonnet]

Yep, udhcp uses a script system to react to a DHCP lease.
Right now Rinkhals has one here: files\3-rinkhals\usr\share\udhcpc\default.script.d\lease-file.script

[IguanaBob]

Actually, I noticed I showed the wrong /etc/resolv.conf. It does actually add it, but leaves 1.1.1.1 and 8.8.8.8 at top so the custom servers may not get used.

root@Rockchip:/root# cat /etc/resolv.conf
nameserver 1.1.1.1
nameserver 8.8.8.8
search REDACTED # wlan0
nameserver 192.168.21.1 # wlan0
nameserver 192.168.21.1 # wlan0

Edit 1: Trying 10 nslookups shows it used 1.1.1.1 every time, so it's not randomly picking from resolv.conf that would be expected.

Edit 2: Adding "options rotate" does not change this behavior, it still always uses the first entry in resolv.conf

[milkpirate]

Yes, could you @jbatonnet change the script to prepend instead of append the DNS settings from the wifi NIC?

Since the resolver tries them in order (top to bottom).

So asking the router first (and only if its not responsing, fall back to the public DNS servers) would make it possible to expose local DNS records to the printer like spoolman.local or similar and avoid hardcoded IPs in the configurations.

Or if you tell me where its done, I could propose a PR.

[IguanaBob]

Functionally addressed in #323