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"Roy" == Roy Arends <roy@dnss.ec> writes:

Roy> Your wild guess is wrong, there are no queries possible that Roy> exceeds > 512 udp size. A QNAME has a maximum length of 255. IIUC, there is nothing in the DNS protocol which limits the Question Section to one QNAME/QTYPE/CLASS tuple. QDCOUNT can be > 1. Though I suppose some could argue that a request which contained > 1 query was unreasonable. [ISTR BIND will reject these with a FORMERR.] And if we consider DDNS requests to be queries -- which in some sense they are -- these can easily be bigger than 512 bytes. Just throw in a few prerequisites and a handful of additions and deletions in the one DDNS transaction. Besides I think the original context of "unreasonable queries" was really about queries which were unreasonable because of the responses they'd provoke, not the size of the queries themselves. ie In the absence of EDNS0 the server is forced to send truncated replies, causing TCP retries. Come to think of it, a discussion of query size is somewhat academic. If a query is going to be more than 512 bytes, the client will have to either use TCP or EDNS0 to send it to the server.