zone transfers sticking on one port?

[Jim Reid]

>>>>> "Barry" == Barry Margolin <barmar at alum.mit.edu> writes:

    >> The port chosen is essentially random. But it's repeatable. The
    >> choice the kernel makes is determined by factors like which
    >> ports are currently in use. So if the overall TCP state of the
    >> host is unchanged between connection attempts, the chances are
    >> the kernel will pick the same ephemeral port number. However
    >> this is an implementation issue for your kernel's TCP/IP stack.

    Barry> BIND asks the OS to select a port when it first starts up.
    Barry> So for the life of that named process it always uses the
    Barry> same port number.

Yes and no. That's certainly how BIND used to work. But the BIND9
servers here don't have a TCP socket for zone transfers even though
they slave several zones. [lsof shows the servers only have (listening)
TCP sockets for ports 53 and 953.] named is creating and destroying
sockets for zone transfers as it needs them. When I've forced one of
these servers to do a zone transfer, it's used a different source port
each time.