On Thu, Feb 18, 2010 at 10:28:39AM -0500, Brian Haley wrote: > Matt Garman wrote: > > Say I have two multicast programs running on the same machine. > > One is a sending program, and one is a receiving program. The > > receiving program has joined the group to which the sender in > > sending. > > > > How does the Linux kernel route these packets? I.e., are the > > packets just pushed out to the switch for routing, or is the > > kernel smart enough to do some "local delivery" and directly > > deliver packets to the listener? > > Multicast packets are always looped-back by default in Linux. You > can turn this behavior off by setting the IP_MULTICAST_LOOP socket > option to zero. So if I'm seeing delays in a local-send-and-receive multicast scenario, the "local loop back" behavior eliminates the networking hardware as the culprit, correct? Next question, then: are there queues/buffers involved in the Linux kernel's multicast implementation? What I am seeing---in exactly a local send and receive situation---are latency problems that look like queueing delays. Where might I start to probe to investigate the source of these delays? Thanks again, Matt -- To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
