Creating a dedicated task from T253666#6166521
Related: we have the issue of ICMP Packet-Too-Big routing: AFAIK Juniper doesn't even try to route a PTB from an intermediate router to the same server as the primary traffic it was referencing. This probably isn't a major issue for the authdns case, because (a) the client recursors should mostly be on server (rather than eyeball) networks with full MTU + (b) the overwhelming majority of all traffic is UDP with small-enough packet sizes to fit any reasonable network. However, it would be nice to be correct for edge cases like recursors in eyeball networks with MTU problems, and future-proof against increasing TCP usage in the future (for cookie init and other blind-injection-avoidance, and also DoTLS and future DNSSEC packet size increases). Cloudflare's generic answer to this problem has been https://github.com/cloudflare/pmtud , but there might be different and/or simpler approaches we want to try as well.