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Date:      Sat, 29 Apr 2023 12:01:38 +0200
From:      Arnaud Houdelette-Langlois <arnaud.houdelette@normandie-univ.fr>
To:        freebsd-net@FreeBSD.org
Subject:   Duplicates IP packets when using CARP and ECMP routes.
Message-ID:  <e57135b2-90a2-b71e-8a7d-b80a2f638b9f@normandie-univ.fr>
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Hi.

We got a freebsd router with both ospf/bpg and multipath routes (ECMP) 
(using the new bird2 with netlink) .

The router got an interface with carp enabled on it (gateway for admin 
vlan).

Packets received on the carp address gets routed on all known routes 
towards destination. Thus, the destination host receives duplicates ip 
packets. (which disrupts most udp based protocols)

Using a simple alias instead of carp solve the problem. Is this a known 
problem, or should I fill a PR ?

-- 
Arnaud Houdelette-Langlois
Administrateur des infrastructures systèmes et réseaux
Normandie Université
+33 2 31 56 69 54

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    <p>Hi.</p>
    <p>We got a freebsd router with both ospf/bpg and multipath routes
      (ECMP) (using the new bird2 with netlink) . <br>
    </p>
    <p>The router got an interface with carp enabled on it (gateway for
      admin vlan). <br>
    </p>
    <p>Packets received on the carp address gets routed on all known
      routes towards destination. Thus, the destination host receives
      duplicates ip packets. (which disrupts most udp based protocols)<br>
    </p>
    <p>Using a simple alias instead of carp solve the problem. Is this a
      known problem, or should I fill a PR ?<br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Arnaud Houdelette-Langlois
Administrateur des infrastructures systèmes et réseaux
Normandie Université
+33 2 31 56 69 54</pre>
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