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I have a server with 2+ network interfaces (pick a number). Each of the interfaces is defined as such:
iface ethx inet dhcp
Each of the interfaces has been assigned an IP address based on its MAC address; that is, the network admin has created a manual DHCP lease for that MAC address and only that MAC address. We are also using sticky-ARPs, meaning that no other MAC address can obtain the IP of another without have the ARP entry cleared.
The problem begins occuring 5 minutes after each NIC obtains its IP address, and continues to appear in the logs in five minute increments. Errors begin showing up in the DHCP server logs indicating that the NICs are attempting to use the IP addresses of other interfaces.
For example, eth0 obtains ip address 220.127.116.11, eth1 obtains address 18.104.22.168, and eth2 obtains 22.214.171.124. The DHCP server soon begins reporting that the MAC address of eth2 is attempting to send traffic through the address of eth0, eth1 is attempting to send traffic through the address of eth2, and so on. Ifconfig shows that the ip and MAC addresses match up properly, as does to the leases in the DHCP server.
If we use only two network interfaces, this problem does not manifest. It only shows up when using more than two interfaces.
Is this a problem with multiple adapters? Can this problem be fixed by using static addresses? Is this problem only evident in Debian Linux?
Enterprise Systems Administrator
Missouri State University
You cannot have network cards in the same box on the the same subnet and achieve any form of routing because the network gets confused as you have found out. They must be on different subnets as described above in order to achieve routing. The boxes attached to each card however, must be on the same subnet as the card they are attached to.