How to create a dummy interface on a machine with mulitple NIC?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5.4

Issue

  • How to create a dummy interface on a machine with mulitple NIC?

Resolution

Note: Dummy interfaces do not use any physical NIC card from the system by default. If Physical interface is to be used as a dummy, it needs to be alias first. Information about this can be found in the following document: How to make alias TCP/IP addresses to a network card (NIC)?

To create a dummy interface:

# modprobe dummy
# ifconfig dummy0 1.2.3.4 netmask 255.0.0.0

Please note that dummy0 should have a static ip-address (to avoid routing problems). How to achieve this:

  1. Enable routing:

    # echo 1 > /proc/sys/net/ipv4/ip_forward
# sysctl -w net.ipv4.conf.eth0.forwarding = 1

  2. Write an iptables rule to forward/accept all the network I/O from dummy0 [ip-addrs] to eth2 [ip-addrs] (something similar to the following):

    # iptables -t nat -I PREROUTING -s 192.168.1.10 -d 192.168.1.20 -j DNAT --to-destination 10.101.100.30

    In this example, dummy0 can be bound to eth2(10.101.100.30).

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