Re: PMTU-D: remember, your load balancer is broken

["Bora Akyol" <akyol () akyol org>]

FYI, there are core routers out there that can support
line rate HW-based fragmentation. I believe this is necessary in any router
with heterogeneous interfaces.

Bora

----- Original Message -----
From: <Valdis.Kletnieks () vt edu>
To: "Paul Vixie" <vixie () mibh net>
Cc: <nanog () merit edu>
Sent: Saturday, June 17, 2000 10:06 PM
Subject: Re: PMTU-D: remember, your load balancer is broken


> On Sat, 17 Jun 2000 11:59:30 PDT, Paul Vixie <vixie () mibh net>  said:
> > Valdis.Kletnieks () vt edu writes:
> > > Has this changed?  Has "fragmentation" become a Great Evil, ... ?
>
> > Yes.  http://research.compaq.com/wrl/techreports/abstracts/87.3.html
says:
> (abstract trimmed)
> >                               Research Report 87/3, December 1987
> >
> >                               87.3 -- Fragmentation Considered Harmful
> >                               Fragmentation is at best a necessary evil;
it
> >                               can lead to poor performance or complete
> >                               communication failure. There are a variety
of
> Yeah, I've known about that for a while.  What I *meant* was:
>
> Has fragmentation been reclassified from "necessary evil that can
> cause problems" to "Great Evil that must be avoided at all costs"?
>
> For instance, we probably all agree that fragging on a core router
> is Bad Juju and should be avoided if at all possible.  On the other
> hand, how far should we jump through hoops (such as PMTU-D etc)
> to avoid fragging on a last-hop modem link from a terminal server
> to a PC?
>
> I already spend far too much of my day (even with a lot of tools)
> sending flame-grams to ISPs who drop us spam, or have open mail relays,
> or start running NTP or tools that query ports 13/37 and forget to open
> the firewall, and then complain about my machine probing them..
>
> Enabling PMTU-D (even if it won't buy *my* boxes that much since their
> local MTU is 1500) and getting people to fix their ICMP configurations
> for the benefit of those sites that WILL profit is an option, but
> only if there's general consensus that it's a fight worth fighting...
>
> Valdis Kletnieks
> Operating Systems Analyst
> Virginia Tech