I used C++ to implement a simple router with a static routing table. It receives ethernet frames and process them: forward them to the right interface, create new frames, etc.
high level design:
handlePacket:
check for type if arp: if arp request: if target mac is broadcast and target ip is the router: send arp response if arp respnse: if mac in the arp cache: send relevant packets out if ip: check if it is legit if to this router: if icmp: if icmp echo: if ip in the cache: reply else: cache it if icmp echo reply: forward it else: forward it
periodicCheckArpRequestsAndCacheEntries: first handle the arp reqest table, and then handle the arp entry table
lookup: use linear search to find the longes matching prefix
problems: It is a tedious project and I had to look into so many details. At first I messsed up the interface used when forwarding a package. Then I messed up the size passed into the checksum function and the file forwarded wouldn't get a reply(because the checksum would be wrong) and all the test files wouldn't appear in the folder Then for some reason the files still wouldn't transmist and after I restarted the vagrant and changed the port number it works, which I don't understand why. Basically when I have a bug I print out everything and just read the output in the router console and try to figure out what is wrong. I went to Seungbae and Siva's office hour for help and I really appreciate their help. I wouldn't have figured it out without them.