It's common for 29West LBM customers who are concerned about single points of failure to ask if LBM can send one message on two different interfaces at once. Unfortunately, there is no single thing an application can do through the socket interface to cause one packet to be sent on two interfaces.
It may seem odd that you can write a single system call that will accept a TCP connection on all of the interfaces on a machine, yet you can't write a single system call that will send a packet out on all interfaces. We think this behavior can be traced back to the presumption that all interfaces will be part of the same internet (or perhaps the same "Autonomous System" or "AS" to use BGP parlance). You generally wouldn't want to send the same packet into your internet more than once. Clearly, this doesn't account for the case where the interfaces on a machine straddle AS boundaries or cases where you actually do want the same packet sent twice (say for redundancy).
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