this is an extract from Tcp/Ip Illustrated (R. Stevens)
.....
When the resolver issues a query and the response comes back with the TC bit set ("truncated") it means the size of the response exceeded 512 bytes, so only the first 512 bytes were returned by the server. The resolver normally issues the request again, using TCP. This allows more than 512 bytes to be returned. Since TCP breaks up a stream of user data into what it calls /segments,/ it can transfer any amount of user data, using multiple segments.
.....
Mike Burger wrote:
Sure about that? My understanding was that TCP is only used for zone file transfer type use, and UDP for queries. I hadn't heard that there was any sort of TCP use for queries.
On Wed, 20 Oct 2004, antonio tuozzo wrote:
This is true! However, normal queries are single UDP requests. DNS system uses TCP only when data size replies is > 512 bytes.
On Wed, Oct 20, 2004 at 06:20:20PM +0200, Crucificator wrote:
As a matter of fact DNS uses both TCP and UDP.
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