-224.0.0.1 is the all-systems multicast address: all +224.0.0.1 is the all-systems multicast address: all datagram sockets appear to be automatically member of this group on all interfaces. This membership cannot be dropped on Linux (you need iptables to filter packets). @@ -304,7 +304,51 @@ Please note that the new features could not be successfully tested on IPv6; these sections thus apply to IPv4 only.
-This document was last modified in April 2009.
++socat version 1.7.0 helps to find more information about incoming packets in +environment variables that can be used in scripts or programs invoked by +socat. The option ip-pktinfo (on non-BSD systems) +or ip-recvdstaddr (on BSD systems) is required to get basic +information about incoming packets. +
+ ++Example: Start a receiver of the following form (tried on Linux): +
+ + +socat -u udp-recvfrom:8888,reuseaddr,ip-add-membership=224.1.0.1:192.168.10.2,ip-pktinfo,fork system:export + + ++Then send a multicast packet from the client: +
+ + +echo |socat -u - udp-datagram:224.1.0.1:8888 + + ++On the server the following text should appear (only interesting lines shown): +
+ ++export SOCAT_IP_DSTADDR="224.1.0.1" +export SOCAT_IP_IF="eth0" +export SOCAT_IP_LOCADDR="192.168.10.2" +export SOCAT_PEERADDR="192.168.10.1" +export SOCAT_PEERPORT="41159" ++ +
+SOCAT_IP_IF shows the interface where the packet entered the server; +SOCAT_IP_LOCADDR shows the IP address of this interface; +SOCAT_IP_DSTADDR shows the target address of the packet; +SOCAT_PEERADDR and SOCAT_PEERPORT are the client socket +values. +
+This document was last modified in May 2009.
Copyright: Gerhard Rieger 2007-2009
License: GNU Free Documentation License (FDL)