RRset limit

Kevin Darcy kcd at daimlerchrysler.com
Sat Jun 3 03:38:52 UTC 2000


Greg Zhang wrote:

> Hello,
>
> What is the limit on the number of record you can have in a
> RRset in both bind v8 and v4?
>
> I've tried to search for it on line. So far to no avail. Any help
> would be appreciated.

I don't think BIND 4 or 8 has any arbitrary limits on the number of RR's
in an RRset in terms of loading them from zone files and storing them in
memory (assuming you have enough memory of course!).

Or are you trying to determine what limit exists on the number of RR's
in an RRset in a DNS *response*? Depends on the transport protocol
used...

With a TCP response, I believe the only real limit would be the size of
the header fields which enumerate the number of RR's in each section of
the response, i.e. "QDCOUNT", "ANCOUNT", "NSCOUNT" and "ARCOUNT", in
RFC 1035 parlance. These are unsigned 16-bit fields, so the theoretical
limit for each would be 65535. But this is technically not an
"RRset" limit, it's a *section* limit: anything else occupying the same
section, e.g. a SIG record, would subtract from that limit.

With a UDP response, a much tighter constraint would be the 512-byte
packet size limit. This would translate into record-number limits
differently, depending on the size of the question section (which
subtracts from the overall available packet space), whether there are
CNAMEs or other record types in the answer section besides the RRset of
interest (which also eat up the packet space), the type of RR's in the
RRset (since different types consume different amounts of space per RR),
and how compressible the labels are.

I believe all of the above would apply to both BIND 4 and 8 (except the
part about SIG of course :-)


- Kevin




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