LPRng Reference Manual: 3 May 2004 (For LPRng-3.8.27) | ||
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This message usually appears when you have been sending a large number of jobs to a network printer or a remote system. The reason for this is a combination the above port 721-731 restriction and the TCP/IP timeouts. For details, see RFC1179 and LPRng, but here is a quick explanation.
A TCP/IP connection is usually specified as between srchost:srcport, desthost:destport, although in practice the order of source (src) and destination (dest) is not important.
When a connection is established, each end of the connection exchanges the necessary flow control and error control information. When a connection is terminated, each end of the connection will not accept another connection from the same host:port that was previously active for a specified timeout period, usually 10 minutes.
Some TCP/IP implementations go further: they will not
allow ANY connection to be
originated (via the bind()
system call or API) from a port that
was active, or accepted on a port that was active for this
timeout period.
Now let us see what happens when we have a client program, which must originate a connection on port 721-731, connect to the server, which waits for a connection on port 515. We first try to make a connection from host:port 1.1.1.1:721 to 1.1.1.2:515. The first time that we make the connection (or the first connection) we succeed. We can transfer a file, etc., and then close the connection. When we try to reconnect from 1.1.1.1:721 to 1.1.1.2:515 we get an error such as "address already in use" or "connection refused".
Luckily, we can use port 722 to originate a connection, and we can connect from 1.1.1.1:722 to 1.1.1.2:515. We continue on, until we come to port 731, and then we need to wait for our timeouts.
SOLUTION:
It appears that most RFC1179 implementations do not check for the exact port range 721-731, but only that the connection originates from a reserved port, i.e. - in the range 1-1023. You can extend the range of ports used by LPRng by changing the
value in the defaults (LPRng/src/common/defaults.c) file or in the lpd.conf file. I recommend the following: This is, in fact, now the default in LPRng software. If you get the infamous malformed from address error message from your spooler, then you will have to set originate_port=721 731, and live with a delayed throughput.