[olug] bad practices at home - not relevant!

[Brian Roberson]

I wonder what the impact of a 1500 byte MTU would be on, let say a usb
cable modem ;-)



-----Original Message-----
From: David Walker [mailto:linux_user at grax.com] 
Sent: Sunday, May 27, 2001 12:32 AM
To: olug at bstc.net
Subject: RE: [olug] bad practices at home - not relevant!


If the MTU values given are fairly standard then outgoing packets should
never have a problem since they will always be ethernet packets and are
not likely to be routed over an X.25 network, therefore they will not
ever hit a router that cannot handle the MTU of 1500 since that is the
lowest likely MTU.

Incoming packets must hit an MTU equal to or less than the router with
the internal IP prior to hitting that router so that that particular
router will never have to fragment their packets or reject them.  @home
can count on the final destination of virtually all packets on their
network being ethernet so couldn't they adjust their routers
accordingly?

-----Original Message-----
From: puzzled [mailto:puzzled]On Behalf Of puzzled
Sent: Saturday, May 26, 2001 11:27 PM
To: olug at bstc.net
Subject: Re: [olug] bad practices at home - not relevant!



     :-)

   A much deserved poke - I've been asked before if the use of RFC1918
(aka private) addresses was an issue in large scale ISP operations and
I've always said that it didn't matter - I'd never really considered the
path MTU discovery aspect.

   I've known the mechanics of PMTU for a long time but I've never seen
an instance of it in action and I spend *a lot* of time watching traffic
with various protocol analyzers.

   Thus far this has been a pretty theoretical discussion - anyone got a
real world example they can share? I'd be happy if someone could come up
with a client/server interaction that shows actual PMTU discovery. If
this can be found I'll set up a unix box on a path where we can vary the
MTU and we'll do some benchmarks on network performance.




Brian Roberson wrote:

> Just an FYI on my quick response & flame on the subject:
> Neal & I ( puzzled at home.com ) go way back and this was a poke at him, 
> not at the group.
>
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