我遇到了一个相当奇怪的问题，我不知道如何调试——我已将服务器从 19.04 更新到 19.10，现在服务器无法再执行 DNS 查询。例如：
$ nslookup google.com
Server: 127.0.0.53
Address: 127.0.0.53#53
** server can't find google.com: SERVFAIL
它运行一个桥接接口，两个虚拟机在其上运行。在虚拟机内部，一切都运行良好。当我在机器启动systemd-resolve后重新启动时，DNS 立即开始工作。唯一的变化是从 19.04 更新到 19.10（并且此服务器已从旧版本的 Ubuntu 不断更新。）我不确定可能出了什么问题，日志看起来与systemd-resolved以前没有什么不同。
网络配置：
$ cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
source /etc/network/interfaces.d/*
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
# auto eno1
iface eno1 inet manual
auto br0
iface br0 inet dhcp
bridge_ports eno1
bridge_fd 5
bridge_stp yes
systemd-resolve --status在我重新启动之前指示没有 DNS：
Global
LLMNR setting: no
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.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-addr.arpa
22.172.in-addr.arpa
23.172.in-addr.arpa
24.172.in-addr.arpa
25.172.in-addr.arpa
26.172.in-addr.arpa
27.172.in-addr.arpa
28.172.in-addr.arpa
29.172.in-addr.arpa
30.172.in-addr.arpa
31.172.in-addr.arpa
corp
d.f.ip6.arpa
home
internal
intranet
lan
local
private
test
Link 11 (vnet1)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 10 (vnet0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 9 (virbr0-nic)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 8 (virbr0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 7 (docker0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 6 (br0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 5 (eno4)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 4 (eno3)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 3 (eno2)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 2 (eno1)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
重新启动后，我得到了正确的 DNS：
Global
LLMNR setting: no
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 192.168.178.2
DNS Servers: 192.168.178.2
DNS Domain: lan
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.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-addr.arpa
22.172.in-addr.arpa
23.172.in-addr.arpa
24.172.in-addr.arpa
25.172.in-addr.arpa
26.172.in-addr.arpa
27.172.in-addr.arpa
28.172.in-addr.arpa
29.172.in-addr.arpa
30.172.in-addr.arpa
31.172.in-addr.arpa
corp
d.f.ip6.arpa
home
internal
intranet
lan
local
private
test
Link 11 (vnet1)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 10 (vnet0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 9 (virbr0-nic)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 8 (virbr0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 7 (docker0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 6 (br0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 5 (eno4)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 4 (eno3)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 3 (eno2)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 2 (eno1)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
iptables -L -n -v
Chain INPUT (policy ACCEPT 1959 packets, 333K bytes)
pkts bytes target prot opt in out source destination
1959 333K LIBVIRT_INP all -- * * 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
2609 940K LIBVIRT_FWX all -- * * 0.0.0.0/0 0.0.0.0/0
2609 940K LIBVIRT_FWI all -- * * 0.0.0.0/0 0.0.0.0/0
2609 940K LIBVIRT_FWO all -- * * 0.0.0.0/0 0.0.0.0/0
2609 940K DOCKER-USER all -- * * 0.0.0.0/0 0.0.0.0/0
2609 940K DOCKER-ISOLATION-STAGE-1 all -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
0 0 DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0
2609 940K ACCEPT all -- br0 br0 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 1462 packets, 209K bytes)
pkts bytes target prot opt in out source destination
1470 212K LIBVIRT_OUT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain DOCKER (1 references)
pkts bytes target prot opt in out source destination
Chain DOCKER-ISOLATION-STAGE-1 (1 references)
pkts bytes target prot opt in out source destination
0 0 DOCKER-ISOLATION-STAGE-2 all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
2609 940K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-ISOLATION-STAGE-2 (1 references)
pkts bytes target prot opt in out source destination
0 0 DROP all -- * docker0 0.0.0.0/0 0.0.0.0/0
0 0 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain DOCKER-USER (1 references)
pkts bytes target prot opt in out source destination
2609 940K RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
Chain LIBVIRT_FWI (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * virbr0 0.0.0.0/0 192.168.122.0/24 ctstate RELATED,ESTABLISHED
0 0 REJECT all -- * virbr0 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable
Chain LIBVIRT_FWO (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- virbr0 * 192.168.122.0/24 0.0.0.0/0
0 0 REJECT all -- virbr0 * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable
Chain LIBVIRT_FWX (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- virbr0 virbr0 0.0.0.0/0 0.0.0.0/0
Chain LIBVIRT_INP (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT udp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:53
0 0 ACCEPT tcp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:53
0 0 ACCEPT udp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:67
0 0 ACCEPT tcp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:67
Chain LIBVIRT_OUT (1 references)
pkts bytes target prot opt in out source destination
0 0 ACCEPT udp -- * virbr0 0.0.0.0/0 0.0.0.0/0 udp dpt:68