On 3/11/12 12:58 PM, Florent Bouron wrote:
Does someone know how a dns server decides to respond based on the size of the response it's about to send?
I'm asking this question as it doesn't seem possible for a server to switch to tcp. Look at this scenario : - client behind firewall (and or NAT) sends a request via UDP. - server "decides" to answer with tcp and creates a session with the client
The server responds using only UDP to a request received via UDP. If the response is "too large," the TC (truncated) bit is set in the response header, indicating to the client that the response wouldn't fit. Upon receiving a response with TC set, a client could then retry the query using TCP - the connection is established outbound from the client to the server. -Mike