What are the size limits on DNS responses? For instance how many ‘A’ resource records can be present in a single DNS response? The DNS response should still be cache-able.
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What are the size limits on DNS responses? For instance how many ‘A’ resource records can be present in a single DNS response? The DNS response should still be cache-able.
The largest guaranteed supported DNS message size is 512 bytes.
Of those, 12 are used up by the header (see §4.1.1 of RFC 1035).
The Question Section appears next, but is of variable length – specifically it’ll be:
Hence the longer your domain name is, the less room you have left over for answers.
Assuming that label compression is used (§4.1.4), each
Arecord will require:i.e. 16 bytes for each A record (§4.1.3).
You should if possible also include your NS records in the Authority Section.
Given all that, you might squeeze around 25 records into one response.