Since it is a reccuring question, I took the time to investigate into winsock keepalive packets.
Here is what Microsoft says about keepalive (full story at http://www.microsoft.com/technet/itsolutions/network/deploy/depovg/tcpip2k.mspx): A TCP keep-alive packet is simply an ACK with the sequence number set to one less than the current sequence number for the connection. A host receiving one of these ACKs responds with an ACK for the current sequence number. Keep-alives can be used to verify that the computer at the remote end of a connection is still available. TCP keep-alives can be sent once every KeepAliveTime (defaults to 7,200,000 milliseconds or two hours) if no other data or higher-level keep-alives have been carried over the TCP connection. If there is no response to a keep-alive, it is repeated once every KeepAliveInterval seconds. KeepAliveInterval defaults to 1 second. TCP keep-alives are disabled by default, but Windows Sockets applications can use the setsockopt function to enable them. TWSocket conatins code which enable keepalive packets. It always had. Using a sniffer, I confirmed that winsock never send keep alive packet on my win xp pro sp2 computer (I tested with a public FTP server on the internet). I added registry keys as explained in the above document: KeepAliveInterval: This parameter determines the interval between keep-alive retransmissions until a response is received. Once a response is received, the delay until the next keep-alive transmission is again controlled by the value of KeepAliveTime. The connection is aborted after the number of retransmissions specified by TcpMaxDataRetransmissions have gone unanswered. KeepAliveTime: The parameter controls how often TCP attempts to verify that an idle connection is still intact by sending a keep-alive packet. If the remote system is still reachable and functioning, it acknowledges the keep-alive transmission. Keep-alive packets are not sent by default. This feature may be enabled on a connection by an application. I used a few seconds interval and alive time. Still not a single keep alive packet on the network ! I modified TWSocket code to add this method: procedure TCustomWSocket.SetKeepAliveOption; var OptVal : Integer; Status : Integer; KeepAliveIn : TTcpKeepAlive; KeepAliveOut : TTcpKeepAlive; BytesReturned : Cardinal; begin OptVal := 1; Status := WSocket_Synchronized_setsockopt(FHSocket, SOL_SOCKET, SO_KEEPALIVE, @OptVal, SizeOf(OptVal)); if Status <> 0 then begin SocketError('setsockopt(SO_KEEPALIVE)'); Exit; end; FillChar(KeepAliveIn, SizeOf(KeepAliveIn), 0); FillChar(KeepAliveOut, SizeOf(KeepAliveOut), 0); BytesReturned := 0; KeepAliveIn.OnOff := 1; KeepAliveIn.KeepAliveInterval := 10000; { 10 seconds retry } KeepAliveIn.KeepAliveTime := 3000; Status := WSocket_WSAIoctl(FHSocket, SIO_KEEPALIVE_VALS, @KeepAliveIn, SizeOf(KeepAliveIn), @KeepAliveOut, SizeOf(KeepAliveOut), BytesReturned, nil, nil); if Status <> 0 then begin SocketError('WSocket_WSAIoctl(SIO_KEEPALIVE_VALS)'); Exit; end; end; By the way I had to add those constants: IOC_UNIX = $00000000; { Do not use this in ows } IOCPARM_MASK = $000007F7; { Parameters must be < 128 bytes } IOC_WS2 = $08000000; IOC_PROTOCOL = $10000000; IOC_VOID = $20000000; { No } IOC_OUT = $40000000; { Copy out } IOC_IN = $80000000; { Copy in } IOC_INOUT = (IOC_IN or IOC_OUT); IOC_VENDOR = $18000000; SIO_RCVALL = IOC_IN or IOC_VENDOR or 1; SIO_RCVALL_MCAST = IOC_IN or IOC_VENDOR or 2; SIO_RCVALL_IGMPMCAST = IOC_IN or IOC_VENDOR or 3; SIO_KEEPALIVE_VALS = IOC_IN or IOC_VENDOR or 4; SIO_ABSORB_RTRALERT = IOC_IN or IOC_VENDOR or 5; SIO_UCAST_IF = IOC_IN or IOC_VENDOR or 6; SIO_LIMIT_BROADCASTS = IOC_IN or IOC_VENDOR or 7; SIO_INDEX_BIND = IOC_IN or IOC_VENDOR or 8; SIO_INDEX_MCASTIF = IOC_IN or IOC_VENDOR or 9; SIO_INDEX_ADD_MCAST = IOC_IN or IOC_VENDOR or 10; SIO_INDEX_DEL_MCAST = IOC_IN or IOC_VENDOR or 11; I checked with MSVC that all constant have correct values. I tryed calling SetKeepAliveOption when the socket is opened, just after linger options and when it is connected in Do_FD_CONNECT. Neither worked. No error but no keep alive packet on the network. I don't know what to try next. I ggogled a lot without finding more interesting informations. Any idea ? -- Contribute to the SSL Effort. Visit http://www.overbyte.be/eng/ssl.html -- [EMAIL PROTECTED] http://www.overbyte.be -- To unsubscribe or change your settings for TWSocket mailing list please goto http://www.elists.org/mailman/listinfo/twsocket Visit our website at http://www.overbyte.be
