On 11 mrt 2008, at 14:38, Dave Thaler wrote: > Note the specific clause that suggests that bridges can generate ICMP > too big messages.
I've seen them do IP(v4) fragmentation, too. >> On a link with variable MTUs the second step is not possible without >> additional communication of per-destination MTUs, and even then >> "invisible" layer 2 devices can get in the way. These layer 2 devices >> can't do step 1 because of hardware limitations. > I don't know what you mean about "can't do step 1". Can you > elaborate? Following topology: H1----X----H2 In the current situation where X is a router, then X can by definition receive the largest packets that H1 can send because H1 and X MUST use the same MTU on their common subnet. If then the subnet towards H2 uses a smaller MTU X can return a too big to H1. For ethernet, the problem doesn't arise today because the MTU is always 1500 bytes. If we now go to multi MTU subnets, H1 could send a packet that is larger than X can receive if H1 happens to have a larger MTU than X. This means that in that case X can't successfully receive the packet, which is of course a prerequisite for generating too big messages. _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
