Comment 0 for bug 1940715

[impact]

when talking to upstream nameservers, systemd-resolved limits its advertised max packet size as 512 in its edns0 opt. However, one of the primary benefits of edns0 is to allow using packet sizes larger than 512, which is the pre-edns0 max packet size.

this results in systemd-resolved failing to handle responses larger than 512 with udp/edns0, and having to fall back to tcp. This is not optimal (since tcp dns imposes significantly higher overhead) and may even cause failures, if a firewall allows udp dns but blocks tcp dns traffic.

[test case]

TBD

[regression potential]

failure to correctly look up dns records, or other problems while performing dns lookups with systemd-resolved

[scope]

this is needed for all releases

this still needs fixing upstream