PMTUD for IPv4 Multicast - How?

Tue Sep 1 00:49:47 UTC 2015

William Herrin wrote:

>> for routers, generating ICMP PTB is as burdensome
>> as generating fragments?
> 
> No, it isn't.

Yes, it is. Generating an ICMP PTB @aclet　is as burdensome as
fragmenting　a packet.

> When a router fragments a packet, it has to fragment the next and the
> next and the next. Maybe tens or hundreds of thousands of packets
> before the end of that one user's session.

Not necessarily, because transport layer can react against fragmented
packets.

> When a router generates a PTB, there is no next. PTB is a soft
> failure. The origin must correct the error (by reducing packet size)

What if, the origin does not reduce packet size?

							Masataka Ohta