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Re: [homenet] DNCP/HNCP Revisited

Gert Doering <gert@space.net> Wed, 18 September 2019 20:57 UTC

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Date: Wed, 18 Sep 2019 22:57:32 +0200
From: Gert Doering <gert@space.net>
To: Ted Lemon <mellon@fugue.com>
Cc: Juliusz Chroboczek <jch@irif.fr>, "Ray Hunter (v6ops)" <v6ops@globis.net>, HOMENET <homenet@ietf.org>
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Subject: Re: [homenet] DNCP/HNCP Revisited
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Hi,

On Wed, Sep 18, 2019 at 04:05:39PM -0400, Ted Lemon wrote:
> On Sep 18, 2019, at 3:39 PM, Juliusz Chroboczek <jch@irif.fr> wrote:
> > Is that not a bug?
> The problem is, how???d the packet get so big that it was fragmented?

If you have a discontinuous L2 MTU, you do not need fragmented packets
to see packets disappear.

Host A has an ethernet MTU of 1500.  Sends a packet with 1400 bytes, no
fragmentation needed.

Somewhere in between is an ethernet bridge that only handles 1350 payload
("L2TPv3 with an outer max packet size capped to something too small to
transport 1518 byte packets inside, and not doing outer fragmentation")

Packet gone.

No fragmentation of any sort involved, just incorrectly set up L2 segments.

(Rule #1 for real world operation: ensure that end system L3 MTU is 
always <= the smallest L2 MTU that the packet might encounter in your 
L2 fabric)


Gert Doering
        -- NetMaster
-- 
have you enabled IPv6 on something today...?

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