Subject: Re: [tcpm] pmtu discovery (RFC 4821)

From: Tim Hartrick <[email-masked]>
Date: Fri, 29 Apr 2011 15:25:13 -0600

Caitlin,

On Fri, 2011-04-29 at 09:39 -0700, Caitlin Bestler wrote:
> On Apr 28, 2011, at 1:13 PM, Tim Hartrick wrote:
> 

> So clearly a larger MTU will always benefit hosts, even if the benefit has been
> properly limited to only restoring the context of a specific TCP message rather
> than requiring the restoration of the context for the full TCP connection.
> 
> The real tradeoff is one of optimizing for the hosts versus the forwarding
> elements. Larger frame sizes make efficient memory allocation in the
> network more problematic. But nobody forces switches or routers to
> support larger MTUs. I can't think of any reason not to take advantage
> when working at L3 and above not to just take what L2 is willing to provide.
> 

If it is free to determine what the L2 will provide end-to-end then this
is obviously true but the previous poster was noting that it was less
than free.  Again, thus the reference to diminishing returns.

tim