Comment 0 for bug 1849733

[impact]

glibc's getaddrinfo() uses EDNS0 to talk to resolved, and it sets its payload limit to 1200. When the response is larger than 1200, resolved will limit the response and set the truncate flag. This causes getaddrinfo() to switch to TCP and request again, but glibc incorrectly keeps the EDNS0 RR opt, with the same 1200 payload limit. Most dns nameservers ignore EDNS0 payload limit for TCP, since per RFC it applies only to UDP, but resolved does not and again marks the response as truncated. This prevents getaddrinfo() from being able to resolve any records with a response over 1200 bytes.

[test case]

use ping or telnet, which use getaddrinfo(), to lookup an A record with a lot of results, like toomany100.ddstreet.org

$ telnet toomany100.ddstreet.org
telnet: could not resolve toomany100.ddstreet.org/telnet: Temporary failure in name resolution

[regression potential]

any regression would likely result in failure to correctly lookup a hostname or to provide the correct response to a local client.

[other info]