我systemd-resolved进入调试模式，试图解决来自这台机器的大量 DNS 查询（tcfe01）。似乎systemd-resolved保留了多个缓存副本，一个用于全局范围（*/*），另一个用于特定网络设备（eno1/*）。从日志看来，似乎只有全局范围 ( */*) 被缓存，而不是 ( eno1/*)。对于第一个查询，我们看到Cache miss两个范围，但对于后续查询，我们得到Positive cache hit全局范围，但又Cache miss是设备范围，我们最终每次都访问 DNS 服务器。
这违背了拥有缓存的全部目的，不仅损害了本地计算机 ( tcfe01) 的性能，而且还不必要地破坏了 DNS 服务器。对这种行为的任何洞察都会非常有帮助。
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Got DNS stub UDP query packet for id 14184
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Looking up RR for google.com IN A.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Switching to DNS server 192.168.10.25 for interface eno1.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Switching to system DNS server 192.168.10.25.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Cache miss for google.com IN A
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Transaction 48281 for <google.com IN A> scope dns on */*.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Using feature level UDP+EDNS0 for transaction 48281.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Using DNS server 192.168.10.25 for transaction 48281.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Sending query packet with id 48281.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Cache miss for google.com IN A
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Transaction 1213 for <google.com IN A> scope dns on eno1/*.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Using feature level UDP+EDNS0 for transaction 1213.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Using DNS server 192.168.10.25 for transaction 1213.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Sending query packet with id 1213.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Processing query...
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Processing incoming packet on transaction 48281. (rcode=SUCCESS)
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Verified we get a response at feature level UDP+EDNS0 from DNS server 192.168.10.25.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Added positive unauthenticated cache entry for google.com IN A 299s on */INET/192.168.10.25
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Transaction 48281 for <google.com IN A> on scope dns on */* now complete with <success> from network (unsigned).
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Freeing transaction 1213.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Sending response packet with id 14184 on interface 1/AF_INET.
Apr 23 16:45:34 tcfe01 systemd-resolved[26041]: Freeing transaction 48281.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Got DNS stub UDP query packet for id 50679
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Looking up RR for google.com IN A.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Positive cache hit for google.com IN A
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Transaction 51371 for <google.com IN A> on scope dns on */* now complete with <success> from cache (unsigned).
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Cache miss for google.com IN A
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Transaction 16504 for <google.com IN A> scope dns on eno1/*.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Using feature level UDP+EDNS0 for transaction 16504.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Using DNS server 192.168.10.25 for transaction 16504.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Sending query packet with id 16504.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Freeing transaction 51371.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Freeing transaction 16504.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Sending response packet with id 50679 on interface 1/AF_INET.
Apr 23 16:45:45 tcfe01 systemd-resolved[26041]: Processing query...
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Got DNS stub UDP query packet for id 50950
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Looking up RR for google.com IN A.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Positive cache hit for google.com IN A
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Transaction 27482 for <google.com IN A> on scope dns on */* now complete with <success> from cache (unsigned).
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Cache miss for google.com IN A
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Transaction 24663 for <google.com IN A> scope dns on eno1/*.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Using feature level UDP+EDNS0 for transaction 24663.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Using DNS server 192.168.10.25 for transaction 24663.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Sending query packet with id 24663.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Freeing transaction 27482.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Freeing transaction 24663.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Sending response packet with id 50950 on interface 1/AF_INET.
Apr 23 16:45:48 tcfe01 systemd-resolved[26041]: Processing query...