Route Chain

A small app to generate a long path in traceroute.

Usage

Run make to compile the app.

Optionally run make install to copy the app to /usr/local/bin.

Run ./route-chain 192.168.0.1/24 192.0.0.1/24 fc00::/64 fd00::/64.

Any number of CIDRs is accepted as parameter.

Then run traceroute 192.0.0.10 (or any address in the CIDRs above), and you will get:

traceroute to 192.0.0.10 (192.0.0.10), 30 hops max, 60 byte packets
 1  192.0.0.2  0.105 ms  0.048 ms  0.039 ms
 2  192.0.0.3  0.037 ms  0.036 ms  0.037 ms
 3  192.0.0.4  0.036 ms  0.039 ms  0.039 ms
 4  192.0.0.5  0.043 ms  0.037 ms  0.037 ms
 5  192.0.0.6  0.036 ms  0.038 ms  0.049 ms
 6  192.0.0.7  0.036 ms  0.060 ms  0.042 ms
 7  192.0.0.8  0.038 ms  0.052 ms  0.041 ms
 8  192.0.0.9  0.036 ms  0.037 ms  0.037 ms
 9  192.0.0.10  0.037 ms  0.037 ms  0.036 ms

Internals

This app is made with speed and efficiency in mind. Specifically:

1. Only 2 memory copies per packet:
   • One necessary copy from TUN device to app's memory region (for receiving)
   • All packet processing happen without extra copies
   • One necessary copy from app's memory region to TUN device (for sending)
2. Reserved space for IP/ICMP header for response packets
   • Used for responding Destination Unreachable messages
   • No need to move data around
3. Incremental checksum updates where possible
   • Used for responding to Pings, only minimal updates needed
4. And it's multithreaded!
   • CPU count automatically detected, multiqueue TUN/TAP used

License

Just do whatever you want.