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Re: Evolution of the IP model - ICMP and MTUs



Iljitsch van Beijnum  - Le 8/18/08 2:37 PM :
On 18 aug 2008, at 11:46, Rémi Després wrote:
Fixing the problem for IPv6 may be worth the pain, but fixing it for IPv4 (the only subject of my comment) would IMO be counterproductive.

Counterproductive?
In my Webster dictionary - 10th edition: "tending to hinder the attainment of a desired goal", the goal being here sucessful IPv6 deployment ;-).

Do you know applications other than NFS on UDP that, needing to transmit longer than than 1280 octet datagrams, impose fragmentation even in IPv6?

Most applications have more than 1200 bytes of data to transmit, so potentially this could be most UDP applications, as well as ALL tunneling mechanisms.

I still wonder what are these applications that, having their preferred datagram sizes exceeding that of Ethernet frame, don't work properly where:
- Path MTUs are smaller than this size.
- Reassembly in destination NATs generates losses.

Any information on this would be appreciated.

Now of course applications try to avoid this issue by sending smaller packets, but that's a terrible solution, because we'll never be able to use bigger packets when our link technologies improve.

This solution is in my understanding quite realistic:
- It doesn't prohibits using large packets on large MTU links. (Your fear is unjustified). - Path MTU Discovery algorithms are designed to detect paths that support large packets.


RD