Re: Smallest Transit MTU

[Dan Hollis <goemon () anime net>]

On Wed, 29 Dec 2004, Florian Weimer wrote:
> * Dan Hollis:
> > On Wed, 29 Dec 2004, Jerry Pasker wrote:
> > > Is there an RFC that clearly states: "The internet needs to transit 
> > > 1500 byte packets without fragmentation."??
> > Actually the bigger problem imo is the number of sites which block ECN
> > http://urchin.earth.li/ecn/
> Why is this a problem?  ECN has to be deployed on routers, and it
> currently isn't.

Because tcp connection endpoints have to implement ECN in order to manage 
the flow.

Many OSes (Linux/bsd/aix/solaris/etc) support ECN but due to the large 
number of braindamaged firewalls out there (http://urchin.earth.li/ecn/), 
it defaults to off.

Any host which tries to negotiate ECN in a tcp connection will run into 
lots of problems as millions of idiotic firewalls drop the packets on the 
floor. Quite often the same firewalls which drop 69/8 on the floor.

Its sad because ECN is quite useful. Though the damage by clueless
network admins blocking 69/8 is worse.

> Cisco seems to offer it on some platforms, but their implementation
> provides a strong incentive to constantly set the ECN flags in a
> certain way, to push the packets into a different QoS class.
> (This is from memory, and it might have been corrected.)

http://www.icir.org/floyd/ecn.html

-Dan