4 ms·
False. IP fragmentation allows the size of a single UDP DNS response to be up to 65535 bytes, regardless of the network MTU.
by venaoy 12y ago
False. IP fragmentation allows the size of a single UDP DNS response to be up to 65535 bytes, regardless of the network MTU.
- callesgg 12y agoIt does not have to to with link, udp or ip it is a limitation of the dns spec. Here is a extention that "fixes" it: https://tools.ietf.org/html/draft-ietf-dnsind-udp-size-02 https://tools.ietf.org/html/draft-ietf-dnsind-udp-size-02 I have not seen that spec extention implemented in the wild. I just found the extention so I have on the other side not looked for it.
- EA597C6C 12y agoEDNS(0) allows for larger responses and is both commonly implemented and widely deployed. http://tools.ietf.org/html/rfc6891 http://tools.ietf.org/html/rfc6891
- peterwwillis 12y agoThe great majority of networks out in the world discard UDP DNS packets bigger than 512 bytes. Firewall admins do it, DNS admins do it, application proxies do it, birds do it, bees do it, even educated fleas do it.... As far as the 65535 limit, from RFC 2671: 4.5.5. Due to transaction overhead, it is unwise to advertise an architectural limit as a maximum UDP payload size. Just because your stack can reassemble 64KB datagrams, don't assume that you want to spend more than about 4KB of state memory per ongoing transaction.