Maximum number of updates in a single transaction

Kevin Darcy kcd at
Fri Feb 10 23:38:40 UTC 2006

Mark Andrews wrote:

>>We are implementing a new service that requires a substantial number 
>>of dynamic updates to be performed on a zone. We are talking of 2K 
>>updates in a single dynamic update transaction.
>>We made some tests with Bind 9.3.2 by sending 60 domain updates in a 
>>single transaction (TCP) and everything works correctly.
>>RFC2136 specify a 16 bit limit to UPCOUNT section in the header, so I 
>>assume that the limit of updates that I can send on a single 
>>transaction is 2^16.
>>What is your recommendation of the maximum number of updates in a 
>>single transaction?
>>I believe that ISC makes validation tests with each BIND release. How 
>>many dynamic updates are sent in the ISC's validation tests?
>>Thank you.
>>Gustavo Lozano
>>NIC Mexico (ccTLD .mx)
>	The limitation is the size of the DNS message.  A individual
>	message can be up to 65535 bytes.
Right, which implies that the real-world limit on number of updates in a 
transaction is going to be far less than 65535 (since each update takes 
at least several bytes), and is going to depend on a number of factors, 
such as: whether and/or how many prerequisites there are, the length of 
the names/RDATAs involved, the extent of label compression, etc.

One question that comes to my mind is: does BIND support sending 
multiple UPDATE transactions over the same TCP connection? Seems like 
there is nothing to forbid this in the RFCs and the precedent has 
already been set in the case of AXFR...

                                                      - Kevin

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