How do I create virtual ethernet devices in linux?

StackOverflow https://stackoverflow.com/questions/2082722

Question

I am testing an implementation of a protocol that talks between two computers using ethernet (not IP). In order to not actually have to have two physical computers, I want to create two virtual ethernet interfaces. These would only be able to talk to each other, so one endpoint program would bind to one interface and the other endpoint would bind to the other.

Is this possible and how do I do it?

Was it helpful?

Solution

You can use VDE2, a virtual switch.

For example (you will need a few terms):

# Install vde2 (assumes Debian/Ubuntu)
sudo aptitude install vde2
# Create the switch and two tap interfaces attached to it
sudo vde_switch -tap tap0 -tap tap1
# Configure the interfaces
sudo ip addr add 10.0.31.10 dev tap0
sudo ip addr add 10.0.31.11 dev tap1
# Start a server
socat - TCP-LISTEN:4234,bind=10.0.31.10
# Alternatively, an echo server:
#socat PIPE TCP-LISTEN:4234,bind=10.0.31.10
# Start a client
socat - TCP:10.0.31.10:4234,bind=10.0.31.11

Type on one side, it will appear on the other.

OTHER TIPS

You can use the "tap" virtual ethernet driver which lets a userspace program pretend to be an ethernet interface. This is a standard kernel feature for some time now (it might not be enabled in your kernel though).

You can use ns3 to emulate a complicated network between two tap devices if you need it: http://www.nsnam.org/

I've had it emulating two switches, a wireless client, and an AP, between two virtualbox instances.

man interfaces man ifconfig

just add a new stanza in /etc/network/interfaces

my example configuration:

iface eth0 inet static
   address 192.168.2.150
   netmask 255.255.255.0
   network 192.168.2.0
   broadcast 192.168.2.255
   gateway 192.168.2.253
   # dns-* options are implemented by the resolvconf package, if installed
   dns-nameservers 8.8.4.4


iface eth0:1 inet static
    address 192.168.2.2
    netmask 255.255.255.0
    network 192.168.2.0
    broadcast 192.168.2.255
    gateway 192.168.2.253
    # dns-* options are implemented by the resolvconf package, if installed
    dns-nameservers 8.8.4.4

--

eth0 has ip 192.168.2.150 while eth0:1 has 192.168.2.2

if you want your own subnet and don't want to bother to use vde.

look at this. In short:

# tunctl -t eth0
Set 'eth0' persistent and owned by uid 0
# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr a6:9b:fe:d8:d9:5e  
      BROADCAST MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:500 
      RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

Or with ip:

# ip tuntap add dev eth0 mode tap
# ip link ls dev eth0
  7: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 500
  link/ether 0e:55:9b:6f:57:6c brd ff:ff:ff:ff:ff:ff

You can use the vconfig command example:

vconfig add eth0 10 #virtual interface eth0.10 will be created

Maybe I'm missing something important.. but isn't this exactly what the loopback (lo) interface is for?

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