Re: [RAM] Tunneling overheads and fragmentation

Gert Doering <gert@space.net> Fri, 20 July 2007 14:04 UTC

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Date: Fri, 20 Jul 2007 16:04:33 +0200
From: Gert Doering <gert@space.net>
To: Robin Whittle <rw@firstpr.com.au>
Subject: Re: [RAM] Tunneling overheads and fragmentation
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Hi,

On Fri, Jul 20, 2007 at 12:34:27AM +1000, Robin Whittle wrote:
> For instance, if all provider and transit routers happily handle
> packets significantly longer than whatever hosts normally produce
> (say 1500 bytes) then adding the encapsulation won't lead to any
> fragmentation.  Is this a reasonable assumption?

No.  As of today, too many links and routers still have issues handling
more than 1500 bytes of IP packets (like "most FastEthernet interfaces on 
Cisco routers", which is still considered "high bandwidth" over here).

> What about routers in end-user networks, or CE routers of providers?

Even worse, due to DSL encapsulation you already end up with an IP MTU
of 1492 bytes or less.

Gert Doering
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