named listening on UDP
Edward Lewis
Ed.Lewis at neustar.biz
Wed Apr 4 13:09:50 UTC 2007
UDP listens where it sends. It's not the same as TCP.
In TCP a "listening" port will accept an segment from an "unknown"
remote address and use that to start a connection. "Known" remote
addresses are kinda demultiplexed into the right inter-process
communication bucket (socket in a BSD environment) and buffered
before being sent into the machine's processing guts. TCP ports that
are not willing to accept connections won't handle "unknown"
remote-sent segments, that's the difference between listening and
not. ("Known" means that there is an established connection.)
UDP does not have the concept of a connection or stream, and in BSD
terminology, all datagrams are delivered to the same socket. It
doesn't matter whether the remote address was seen before or not.
At 8:25 -0400 4/4/07, Jeff Lightner wrote:
>Was the original issue misstated? You said it was "listening" on these
>ports. Outbound queries wouldn't be "listening" - they'd simply be
>established when needed.
--
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Edward Lewis +1-571-434-5468
NeuStar
Sarcasm doesn't scale.
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