Hi, Do transit routers in the wild actually get to do IP fragmentation these days? I was wondering if routers actually do it or not, because the source usually discovers the path MTU and sends its data with the least supported MTU. Is this true? Even if this is, then this would break for multicast IP. The source cannot determine which receivers would get interested in the traffic and what capacities the links connecting them would support. So, a source would send IP packets with some size, and theres a chance that one of the routers *may* have to fragment those IP packets before passing it on to the next router. I would wager that the vendors and operators would want to avoid IP fragmentation since thats usually done in SW (unless you've got a very powerful ASIC or your box is NP based). Thanks, Glen