Re: New Version Notification for draft-bonica-6man-frag-deprecate-00.txt

[Glen Turner <[e-mail]>]

On 24/06/2013, at 8:41 AM, Fred Baker (fred) wrote:
> 
> I'm in a similar case with respect to protocols above IPv6 (OSPF and NFS/UDP come quickly to mind) that depend on fragmentation to deal with the issue. I think the Robustness Principle tells us that such applications SHOULD figure out how to live with PMTU, but it also tells us that we can't deprecate fragmentation unless all known instances that depend on it have defined practical work-arounds. I suspect that this would imply the re-creation of the fragmentation feature in an intermediate protocol, which seems like a lot of work with little real gain.

Calculating the PMTU for UDP protocols is left to applications, the sockets API doesn't do this under the hood like it does for TCP. As a result most UDP-using applications don't probe the PMTU. This is the case for both IPv4 and IPv6, although the effect with IPv6 is lost connectivity rather than in-flight fragmentation.

Some small changes to the socket API for unconnected protocols would make life substantially better for RADIUS implementors (and, I imagine, DNS). We're more than happy to repeatedly pass the same application protocol data unit into the socket whilst the socket probes the path MTU.

-glen