TCP/IP Send-Q

[Gavin Kreuiter]

I have an ESTABLISHED socket connection between two applications on two systems. The client app performs a successful socket write(), but the server app (sometimes) does not receive the data. Not surpising, because netstat shows that the local Send-Q contains the data.

Stevens says that this only happens if Nagel is disabled (not applicable), or if the remote receive Q is full (not true). So what else could be the problem? Network hardware? The connect() *always* succeeds, but data is *sometimes* sent, and *sometimes* held in the local TCP Send-Q.

[rohit]

not 100% sure

if you are using ioctl(reuseaddr) then are you using SO_LINGER in the set sockopt.

how many hops are the clients and the server away...any routers in between . kind of network ?? .

if the connection is establised and you are using tcp protocols then it is not possible generally that you get the wrong confirmation . it's a threesome i mean three way communication.

[darkmatter]

Usually, a server will fork() after accept() to process multiple connections. In that case, writing to a socket will be handled at the TCP layer, so that the remote host will have data in the Recv-Q until the child performs a read.

This server was only handling a single connection (although still calling listen() with the typical backlog of 50). Because an accept() was NOT being made for the SECOND connection, the data remained in the Send-Q of the local host.

QED
(but took a long time to solve)