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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. 1. 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. 2. 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. $ ./configure $ make Makefile currently does not have install targets. lwip-tap works in-place in the source directory. Copy it to anywhere if you like. 3. 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 4. 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 5. 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 6. 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 7. 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 8. 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) 9. 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, $ configure --enable-debug $ make which compiles all object files with LWIP_DEBUG set to 1 and adds another option -d to lwip-tap.
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lwip-tap is a test application for experiments with lwIP (a lightweight TCP/IP stack) and debugging of lwIP-based code.
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