The mcast directive is used to configure a multicast[1] communication path.
The syntax of an mcast directive is:
mcast dev mcast-group udp-port ttl 0
dev - IP device to send/rcv heartbeats on
mcast-group - multicast[2] group to join (class D multicast address 224.0.0.0 - 239.255.255.255). For most Heartbeat[3] uses, the first byte should be 239.
port - UDP[4] port to sendto/rcvfrom (set this to the same value as udpport[5])
ttl - the ttl value for outbound heartbeats. This affects how far the multicast packet will propagate. (0-255). Set to 1 for the current subnet. Must be greater than zero.
A sample mcast directive is shown below:
mcast eth0 239.0.0.1 694 1 0
This directive has a few more parameters than it should.
Wikipedia[2], The TCP/IP guide[6]
| [1] | http://en.wikipedia.org/wiki/Multicast |
| [2] | http://en.wikipedia.org/wiki/Multicast_address |
| [3] | http://www.linux-ha.org/Heartbeat |
| [4] | http://en.wikipedia.org/wiki/User_Datagram_Protocol |
| [5] | http://www.linux-ha.org/ha.cf/UdpportDirective |
| [6] | http://www.tcpipguide.com/free/t_IPMulticastAddressing.htm |
This information provided courtesy of the Linux-HA project at http://linux-ha.org/