lwip-tap

lwip-tap is an application of "lwIP - A Lightweight TCP/IP Stack" which is a small, user-space implementation of the TCP/IP protocol stack. Using lwip-tap, you can easily plug an instance of lwIP to Linux Bridge or Open vSwitch through TAP devices. lwip-tap supports multiple network interfaces, so that it also works as a router. A wide range of different network topologies can be built flexibly.

System Requirement

As of now, lwip-tap has been developed only in Linux, more precisely Arch Linux with latest updates. The original tapif driver available in the lwip-contrib, however, includes code chunks for other environments as well. Although lwip-tap is fully supported only in Linux right now, it should work on any environment that supports TAP/TUN-like devices if the tapif driver is updated.

Build

Clone the git repository from GitHub and initialize submodules,

$ git clone git://github.com/takayuki/lwip-tap.git $ cd lwip-tap $ git submodule init $ git submodule update

GNU make is required to build lwip-tap. A compile-time option to enable debugging facilities lwIP provides is available. See "8. Debugging" below. $ cd lwip;git apply ../lwip.patch $ make

Makefile currently does not have install targets. lwip-tap works in-place in the source directory. Copy it to anywhere if you like.

Example: Running lwip-tap with a transient TAP device

The quickest, but less flexible way to run lwip-tap is, having it create a transient TAP device for you,

#lwip-tap -i addr=172.16.0.2,netmask=255.255.255.0,gw=172.16.0.1

In this example, lwip-tap (1) creates a transient TAP device, (2) assign 172.16.0.1 to the tap, (3) adds a route 172.16.0.1/255.255.255.0 to the tap, (4) links an instance of lwIP to the tap, and (5) assign 172.16.0.2 to the interface of the lwIP. To check if the lwIP is working,

# ping 172.16.0.2

Example: Attach lwip-tap to a persistent TAP device

For more flexible network settings, all the steps mentioned above can be made separately using persistent TAP devices,

  # ip tuntap add dev tap0 mode tap
  # ip link set dev tap0 up
  # ip addr add 172.16.0.1/24 dev tap0
  # lwip-tap -i name=tap0,addr=172.16.0.2,netmask=255.255.255.0,gw=172.16.0.1

  # ping 172.16.0.2

Example: Use DHCP with a persistent TAP device

If you omit an address to an instance, lwip-tap automatically uses DHCP.

lwip-tap -i name=tap0

Example: Run lwip-tap with Open vSwitch

Add br0 (172.16.0.1),

  # ovs-vsctl add-br br0
  # ip link set dev br0 up
  # ip addr add 172.16.0.1/24 dev br0

Add tap0 to br0,

  # ip tuntap add dev tap0 mode tap
  # ip link set dev tap0 up
  # ovs-vsctl add-port br0 tap0

Run a lwip-tap on tap0 (172.16.0.2),

  # lwip-tap -i name=tap0,addr=172.16.0.2,netmask=255.255.255.0,gw=172.16.0.1

  # ping 172.16.0.2

Example: Run lwip-tap as a router

Add br0 (172.16.0.1),

  # ovs-vsctl add-br br0
  # ip link set dev br0 up
  # ip addr add 172.16.0.1/24 dev br0
  # ip route add 172.16.1.0/24 via 172.16.0.2

Add br1 (without IP address),

  # ovs-vsctl add-br br1
  # ip link set dev br1 up

Add tap0 to br0,

  # ip tuntap add dev tap0 mode tap
  # ip link set dev tap0 up
  # ovs-vsctl add-port br0 tap0

Add tap1 and tap2 to br1,

  # ip tuntap add dev tap1 mode tap
  # ip link set dev tap1 up
  # ovs-vsctl add-port br1 tap1

  # ip tuntap add dev tap2 mode tap
  # ip link set dev tap2 up
  # ovs-vsctl add-port br1 tap2

Run one lwip-tap on tap2 (172.16.1.2),

  # lwip-tap \
      -i name=tap2,addr=172.16.1.2,netmask=255.255.255.0,gw=172.16.1.1

Run another lwip-tap on tap0 (172.16.0.2) and tap1 (172.16.1.1), which is a router between 172.16.0.2/24 and 172.16.1.1/24,

  # lwip-tap \
      -i name=tap0,addr=172.16.0.2,netmask=255.255.255.0,gw=172.16.0.1 \
      -i name=tap1,addr=172.16.1.1,netmask=255.255.255.0

  # ping 172.16.0.2
  # ping 172.16.1.1
  # ping 172.16.1.2

Use iperf to Test

1. ./lwip-tap -i addr=172.16.0.3,netmask=255.255.255.0,gw=172.16.0.1,name=tap2 -s
2. iperf -c 172.16.0.3 -p 5001

Build-in Applications

lwip-tap has currently three built-in applications which has been integrated from lwip-contrib for debugging purposes. All applications are disabled by default. Use command-line options to enable those services.

• echo (port 7) in TCP/UDP (-E)
• chargen (port 19) in TCP (-C)
• http (port 80) in TCP (-H)

Debugging

lwIP has a compile-time option for debugging which is disable by default. To enable it, you need to rebuild lwip-tap giving an option to configure,

$ make

which compiles all object files with LWIP_DEBUG set to 1 and adds another option -d to lwip-tap.

other

• arp
• iperf -c 192.168.28.33 -p 5001
• iperf -s -B 192.168.28.33

install tunctl

• http://www.rpmfind.net/linux/rpm2html/search.php?query=tunctl download tunctl
• tunctl -t tap0
• ifconfig tap0 inet 192.168.28.33 netmask 255.255.255.0 up