Arch Linux

musbur

Member

Registered: 2022-01-14

Posts: 71

[SOLVED] systemd-resolved missing local DNS Server

I just set up a second Arch system. Networking uses iwd + systemd-resolved on both machines (actually the same machine but different hard drive). I noticed weird networking behavior and found a difference in the output of resolvectl. The block "Link 4 (wlan0)"  on the good setup is missing in the bad setup. I can't find the config file that is responsible for this. /etc/system/network/25-wireless.network is the same on both machines (just copied over, like /var/lib/iwd.) /etc/resolv.conf is a symlink to /run/systemd/resolve/stub-resolv.conf on both systems.

That said, I find it weird that the bad system can find some sites (arch, google) and not others (reddit, duckduckgo). Why is that?

I just noticed that "ip route" on the bad system doesn't output anything at all, while on the good system it shows a default route via my DSL router.

Bad system, output from resolvectl:

Global
           Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: stub
  Current DNS Server: 2606:4700:4700::1111#cloudflare-dns.com
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 9.9.9.9#dns.quad9.net
                      8.8.8.8#dns.google 2606:4700:4700::1111#cloudflare-dns.com
                      2620:fe::9#dns.quad9.net 2001:4860:4860::8888#dns.google

Link 2 (enp0s31f6)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Link 3 (wwp0s20f0u6)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Link 5 (wlan0)
    Current Scopes: LLMNR/IPv6 mDNS/IPv6
         Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Good system:

Global
           Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: stub
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 9.9.9.9#dns.quad9.net
                      8.8.8.8#dns.google 2606:4700:4700::1111#cloudflare-dns.com
                      2620:fe::9#dns.quad9.net 2001:4860:4860::8888#dns.google

Link 2 (enp0s31f6)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

Link 4 (wlan0)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.111.1
       DNS Servers: 192.168.111.1 fd00::e228:6dff:fe06:57ac
                    2a02:3100:8287:8500:e228:6dff:fe06:57ac
     Default Route: yes

Link 5 (wwp0s20f0u6)
    Current Scopes: none
         Protocols: -DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
     Default Route: no

I got it. For some reason, systemd-networkd wasn't running, I must have forgotten to enable it. It took me a long time to figure that out; the fact that the network "partially" worked threw me a bunch of curved balls.

Last edited by musbur (2025-03-13 13:09:18)

Scimmia

Fellow

Registered: 2012-09-01

Posts: 12,530

Re: [SOLVED] systemd-resolved missing local DNS Server

Well you have no IPv4 on the 'bad' system, does it even have an IPv4 address in `ip addr`?

musbur

Member

Registered: 2022-01-14

Posts: 71

Re: [SOLVED] systemd-resolved missing local DNS Server

Sure does. I mean the system is "half working" (I'm using it right now). "ip addr" looks good, "ip route" has nothing. But I don't know if the routing or the resolver is the problem, see output from journalctl at the bottom.

~$ cat /etc/systemd/network/25-wireless.network 
[Match]
Name=wlan0

[Link]
RequiredForOnline=routable

[Network]
DHCP=yes
IgnoreCarrierLoss=3s
~$ 
~$ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether e8:6a:64:bd:cd:97 brd ff:ff:ff:ff:ff:ff
    altname enxe86a64bdcd97
4: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether d0:c6:37:c4:68:41 brd ff:ff:ff:ff:ff:ff
    inet6 2003:e4:5f2d:a401:d2c6:37ff:fec4:6841/64 scope global dynamic mngtmpaddr proto kernel_ra 
       valid_lft 86377sec preferred_lft 86377sec
    inet6 fe80::d2c6:37ff:fec4:6841/64 scope link proto kernel_ll 
       valid_lft forever preferred_lft forever
~$
~$ journalctl -u
-- Boot 63dcfb5645974dc3b3f1ec51753ae37e --
Mar 12 19:40:34 jenna-mob systemd[1]: Starting Network Name Resolution...
Mar 12 19:40:35 jenna-mob systemd-resolved[522]: Positive Trust Anchors:
Mar 12 19:40:35 jenna-mob systemd-resolved[522]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Mar 12 19:40:35 jenna-mob systemd-resolved[522]: . IN DS 38696 8 2 683d2d0acb8c9b712a1948b27f741219298d0a450d612c483af444a4c0fb2b16
Mar 12 19:40:35 jenna-mob systemd-resolved[522]: Negative trust anchors: home.arpa 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-addr.arpa 21.172.in-add>
Mar 12 19:40:35 jenna-mob systemd-resolved[522]: Using system hostname 'jenna-mob'.
Mar 12 19:40:35 jenna-mob systemd[1]: Started Network Name Resolution.
Mar 12 19:43:25 jenna-mob systemd-resolved[522]: Switching to fallback DNS server 1.1.1.1#cloudflare-dns.com.

Scimmia

Fellow

Registered: 2012-09-01

Posts: 12,530

Re: [SOLVED] systemd-resolved missing local DNS Server

No, it doesn't, it only has IPv6. The issue is not routing or the resolver, it's in DHCP.