Create dummy interfaces with `ip` cmd

dummy.md

Useful when you want to do cross-domain testing with a single machine

root:~# lsmod 

root:~# modinfo dummy
filename:       /lib/modules/3.12.8-1-ARCH/kernel/drivers/net/dummy.ko.gz
alias:          rtnl-link-dummy
license:        GPL
depends:        
intree:         Y
vermagic:       3.12.8-1-ARCH SMP preempt mod_unload modversions 
parm:           numdummies:Number of dummy pseudo devices (int)

root:~# ip link add name faker type dummy
root:~# ip link
4: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether fa:1f:82:e3:b6:ef brd ff:ff:ff:ff:ff:ff
5: faker: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 06:05:25:3d:c9:37 brd ff:ff:ff:ff:ff:ff

root:~# ip addr add 10.1.2.3/24 dev faker
root:~# ip route
root:~# ip addr
4: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether fa:fa:82:a3:c6:cf brd ff:ff:ff:ff:ff:ff
5: faker: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default qlen 1000
    link/ether 06:25:35:2d:e9:27 brd ff:ff:ff:ff:ff:ff
    inet 10.1.2.3/24 scope global faker
       valid_lft forever preferred_lft forever

root:~# ping 10.1.2.3
PING 10.1.2.3 (10.1.2.3) 56(84) bytes of data.
64 bytes from 10.1.2.3: icmp_seq=1 ttl=64 time=0.029 ms