From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Lunn <andrew@lunn.ch>
Subject: Re: Debugging Ethernet issues
Date: Sun, 13 Nov 2016 04:09:19 +0100
Message-ID: <20161113030919.GA2892@lunn.ch>
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Cc: netdev <netdev@vger.kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Mans Rullgard <mans@mansr.com>,
        Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Zach Brown <zach.brown@ni.com>,
        Shaohui Xie <shaohui.xie@nxp.com>,
        Tim Beale <tim.beale@alliedtelesis.co.nz>,
        Brian Hill <brian@houston-radar.com>,
        Vince Bridgers <vbridgers2013@gmail.com>,
        Balakumaran Kannan <kumaran.4353@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sebastian Frias <sf84@laposte.net>,
        Kirill Kapranov <kapranoff@inbox.ru>
To: Mason <slash.tmp@free.fr>
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> When connected to a Gigabit switch
> 3.4 negotiates a LAN DHCP setup instantly
> 4.7 requires over 5 seconds to do so

When you run tcpdump on the DHCP server, are you noticing the first
request is missing?

What can happen is the dhclient gets started immediately and sends out
its first request before auto-negotiation has finished. So this first packet
gets lost. The retransmit after a few seconds is then successful.

     Andrew