Caching learned MSS/MTU values

[Hannes Frederic Sowa]

On Thu, Oct 17, 2013 at 09:05:24AM -0700, Jason Fesler wrote:
> I'm once again considering trying to improve on the test-ipv6.com PMTUD
> failure detection. Due to limitations on the client side I can't use raw
> sockets to generate test packets. The client is JavaScript and runs in a
> browser; all I can do is try fetching urls from multiple locations, each
> with a different MTU.
> 
> I know that the various operating systems tend to cache any PMTUD issues
> that they can detect; future connections to that destination will use
> smaller packets accordingly. What I can not see to find is an adequate
> description of what granularity this gets cached with. /128? /64?   Also, I
> the absence of Packet Too Big messages, what does each OS do?

Linux, too, does cache on /128 basis. In the absence of PTB the connection
will get stuck. ;)

Greetings,

  Hannes