Re: Fragmentation / MTU Discovery

From: Clifford Kite (kite@see.signature.id)
Date: 02/25/03 

From: Clifford Kite <kite@see.signature.id>
Date: Tue, 25 Feb 2003 08:45:23 -0600

Douglas Cowan <news@removethisbitdacowan.co.uk> wrote:
> I had been receiving occasional 1500 byte ICMP echo request packets
> to my Linux-box router, and had been wondering what they were. It
> appears they are MTU path discovery attempts.

> The MTU for my DSL connection is 1458 (PPPoA), and this means that
> receiving a 1500 byte echo-request with DF (don't fragment) set
> should result in my router sending back a destination-unreachable
> fragmentation needed with the MTU attached (code 3 / 4)?

> Instead, it appears just to send an echo-reply back, which is indeed
> fragmented -- so it's completely ignoring the DF request.

I don't think so. It seems to me that the router simply generates
an echo-reply since it is not forwarding them. 

-- 
Clifford Kite                Email: "echo xvgr_yvahk-ccc@ri1.arg|rot13"
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