On Mon, 10 May 2004 10:55:43 +0900 Masataka Ohta <mohta@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Dean Anderson; > > > A number of commercial > > products and applications do rely on PMTU to work, and will > > do an PATH MTU discovery, and send the MTU sized packets with > > DF (don't frag). > > and send packets larger than MTU expecting to receive ICMP > errors in vain. > > Read the original mail of the thread on the reality. > The problem identified has nothing to do with the concept or typical implementations of PMTUD being broken. RFC1192 (http://www.rfc-editor.org/rfc/rfc1191.txt) is the spec for PMTUD. The issue that PMTUD is addressing is : "1. Introduction When one IP host has a large amount of data to send to another host, the data is transmitted as a series of IP datagrams. It is usually preferable that these datagrams be of the largest size that does not require fragmentation anywhere along the path from the source to the destination. (For the case against fragmentation, see [5].) This datagram size is referred to as the Path MTU (PMTU), and it is equal to the minimum of the MTUs of each hop in the path. A shortcoming of the current Internet protocol suite is the lack of a standard mechanism for a host to discover the PMTU of an arbitrary path." PMTUD is a performance optimisation, specifically a throughput optimisation. The problem being discussed is directly caused by broken firewall/NAT devices or configurations, blocking network management traffic (ie. ICMP Destination Unreachable, Fragmentation Needed and Don't Fragment was Set) that they should be permitting. Regards, Mark. _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf