'Re: [systemd-devel] Why contacting a 'random address' is necessary'

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List:       systemd-devel
Subject:    Re: [systemd-devel] Why contacting a 'random address' is necessary
From:       "Harry G. Coin" <hgcoin () gmail ! com>
Date:       2021-04-23 14:29:03
Message-ID: d9c40b06-6a9d-1de7-4134-6eba1d320090 () gmail ! com
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On 4/22/21 11:00 AM, Mantas Mikul=C4=97nas wrote:
> ...
> I'm curious about what brought this problem into existence in the
> first place. Why *is* it necessary to contact a random address within
> the network? (If it's to check that the physical interface is working,
> then just the fact that you somehow acquired a lease would be enough. n=
o?)
>
The only non-destructive way I've found to test whether a real or
virtual nic interface computes packet checksums properly is to send a
small packet to a random address temporarily added to the suspect
interface.=C2=A0 If a bad udp checksum is detected, invert
tx-checksum-ip-generic.

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    <div class="moz-cite-prefix">On 4/22/21 11:00 AM, Mantas Mikulėnas
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CAPWNY8X_ZRsQd6ijH+um+FnfWRV5BrFA-SawxRydEAzWuZDQvA@mail.gmail.com">
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        <div class="gmail_quote">...<br>
          <div>I'm curious about what brought this problem into
            existence in the first place. Why *is* it necessary to
            contact a random address within the network? (If it's to
            check that the physical interface is working, then just the
            fact that you somehow acquired a lease would be enough. no?)</div>
        </div>
        <div><br>
        </div>
      </div>
    </blockquote>
    <p>The only non-destructive way I've found to test whether a real or
      virtual nic interface computes packet checksums properly is to
      send a small packet to a random address temporarily added to the
      suspect interface.   If a bad udp checksum is detected, invert
      tx-checksum-ip-generic.</p>
    <p><br>
    </p>
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