Multiple DHCPACK on vlan and native lan

[Joerg Pareigis]

Hi,
I did notice duplicate answers from DHCP Server. And I don't understand why!

The DHCP-Server has 2 Interfaces eth0 and eth1.
Both are bonded to bond0 with LACP connected to the switch.
VLAN 1 is native configured without tagging, just an IP address on bond0.
VLAN 2-6 are configured using 802.1q each with an IP address.

DHCP requests coming in on native vlan1 (bond0) are correct answered by Server.
But requests coming in on any tagged vlan seems to be seen twice by server on vlan AND bond0 interface.
They will be replyed on both interfaces. With an ACK on vlan and a NACK on bond0.

Why and how can this be happen?

I sniffered with tcpdump on bond0:
Only one request with vlan tag and two replys vlan+native:
18:18:08.383264 58:1f:aa:76:35:51 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 346: vlan 3, p 0, ethertype IPv4,
0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 58:1f:aa:76:35:51, length 300
18:18:08.391153 00:0e:0c:68:7a:00 > 58:1f:aa:76:35:51, ethertype 802.1Q (0x8100), length 346: vlan 3, p 0, ethertype IPv4,
192.168.8.1.67 > 192.168.8.25.68: BOOTP/DHCP, Reply, length 300
18:18:08.391658 00:0e:0c:68:7a:00 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 342: 192.168.2.1.67 >
255.255.255.255.68: BOOTP/DHCP, Reply, length 300


In Syslog:
DHCP-Server sees two requests:
Nov 26 18:18:08 gate dhcpd: DHCPREQUEST for 192.168.8.25 from 58:1f:aa:76:35:51 via vlan3
Nov 26 18:18:08 gate dhcpd: DHCPACK on 192.168.8.25 to 58:1f:aa:76:35:51 via vlan3
Nov 26 18:18:08 gate dhcpd: DHCPREQUEST for 192.168.8.25 from 58:1f:aa:76:35:51 via bond0: wrong network.
Nov 26 18:18:08 gate dhcpd: DHCPNAK on 192.168.8.25 to 58:1f:aa:76:35:51 via bond0

-- 
MfG, Joerg