<p>J’ajoute un VLAN tagué sur eth0 :</p>
<pre><code class="lang-auto">#ip link add link eth0 name eth0.20 type vlan id 20
</code></pre>
<p>Ce qui donne :</p>
<pre><code class="lang-auto">#ip link
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 9c:c7:a6:95:65:1c brd ff:ff:ff:ff:ff:ff
....
12: eth0.20@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
link/ether 9c:c7:a6:95:65:1c brd ff:ff:ff:ff:ff:ff
#ip -d link show eth0.20
70: eth0.20@eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
link/ether 9c:c7:a6:95:65:1c brd ff:ff:ff:ff:ff:ff
vlan id 20 <REORDER_HDR>
#cat /proc/net/vlan/config
VLAN Dev name | VLAN ID
Name-Type: VLAN_NAME_TYPE_RAW_PLUS_VID_NO_PAD
eth0.234 | 234 | eth0
eth0.20 | 20 | eth0
</code></pre>
<p>Maintenant je lance dhclient :</p>
<pre><code class="lang-auto">#dhclient -d -v -1 eth0.20
</code></pre>
<p>Ce que je vois dans tcpdump est une trame DHCP discovery non taguée :</p>
<pre><code class="lang-auto">#tcpdump -i eth0 -XX
0x0000: ffff ffff ffff 9cc7 a695 651c 0800 4500
^^^^
</code></pre>
<p>Pourquoi n’est-elle pas taguée ?</p>
<p>Le module 802.1q semble être utilisé :</p>
<pre><code class="lang-auto">#lsmod | grep 8021q
8021q 28324 0
garp 14311 1 8021q
</code></pre>
<p>(OS : SLES11SP2 kernel 3.0.13-0.27-default)</p>
<p>D’ailleurs, le reste du trafic n’est pas tagué non plus (du moins tcpdump ne l’affiche pas)…</p>
<p><strong>Mise à jour 16 octobre</strong></p>
<pre><code class="lang-auto"> # tcpdump -Uw - | tcpdump -i eth0 -en -r - &
[1] 7310
tcpdump: WARNING: eth0: no IPv4 address assigned
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
dhclient -d -v -1 eth0.20
Internet Systems Consortium DHCP Client 4.2.3-P2
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Listening on LPF/eth0.20/9c:c7:a6:95:65:1c
Sending on LPF/eth0.20/9c:c7:a6:95:65:1c
Sending on Socket/fallback
DHCPDISCOVER on eth0.20 to 255.255.255.255 port 67 interval 3
reading from file -, link-type EN10MB (Ethernet)
18:49:14.437882 9c:c7:a6:95:65:1c > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 347: 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 9c:c7:a6:95:65:1c, length 305
^^^^^^
</code></pre>
<p>Donc, toujours pas de tag affiché ici.</p>
<p>Mais effectivement, le compteur de transmission pour eth0.20 dans /proc/net/dev s’incrémente bien lors de l’exécution de dhclient…</p>
<hr>
<p><em>Source : <a href="https://www.isc.org/software/dhcp/" rel="noopener nofollow ugc">Server Fault</a></em></p>
