CS536 Wireless Router Project

CS 53600 wireless router project

Compilation

• Run make clean to clear object files and executable
• Run make to create object files and executables
• Run ./router (as root) or sudo ./router

Functionality

• Connects to the Internet (e.g., to an ISP’s modem)
• Also acts as a Wi-Fi access point and offers Internet service to one or more hosts
  • Assigns an IP address to each via DHCP --> DONE
  • Forwards packets between Wi-Fi hosts and the Internet
    • Handles ICMP (ping) --> DONE
    • Handles UDP
    • Handles TCP
  • Performs NAPT translation before forwarding a packet

Hints

• When the router starts, it will receive the IP address of a default router from the ISP
• Using threads allows easy access to shared variables (e.g., the NAT translation table)
• Start with DHCP using a normal socket and the normal stack; if you decide to write your own IP/UDP modules, you can switch to the raw socket later
• You will need to figure out how to assign IP addresses
  • The ISP will already use a non-routable address
  • You must decide whether a Wi-Fi host can ping the ISP router (in this case, your laptop)
• Remember that changing header fields mandates recomputing checksums
• You need to obtain the IP and Ethernet address of the MyRouter VM on the NAT interface
• If you decide to use the normal stack on the Wi-Fi interface (as opposed to doing all protocols via a raw socket), you must set the interface to "UP" and assign an IP address

Tasks

• NAT box
  • We plan to have 2 hash tables, one to hash the internal IP address and port (expressed as a concatenated string) to the index of the combined entry, and the other hashes the external port to the index of the combined entry
    • We plan to use a rolling hash function to hash a string to an integer index. Additionally, our hash table uses chaining for collision handling.
  • The thread labeled “outgoing NAT" repeatedly
    • Reads the next packet from a Wi-Fi host
    • Ignores any packet sent to the router itself
    • Performs NAPT translation for a TCP/UDP/ICMP packet
      • Recompute checksums for IP header, TCP/UDP headers (new port nums, pseudo-header)
    • Sends the translated packet out the raw socket to the default router
  • The thread labeled “incoming NAT” repeatedly
    • Reads the next packet from the Internet
    • Ignores any packet that does not match NAT table entries
    • Performs NAPT translation on a TCP/UDP.ICMP packet
      • Recompute checksums for IP header, TCP/UDP headers (new port nums, pseudo-header)
    • Sends the translated packet to the correct Wi-Fi host
  • Recompute checksums (on UDP and TCP packets)
• DHCP Server
  • Assign IP addresses to new hosts
  • Idea: for the current network, assign 192.168.1.x (leaving the other network to be 192.168.0.x)
• Management Application
  • Be able to perform the following
    • Dump the NAT table on the router
    • TBC

Design Decisions

Lease

• Leases are defined when DHCP_REQUEST packets are received.
• Existing leases are checked and cleaned out when expired only when DHCP_REQUEST packets are received because that is the only time a lease matters.
• When a DHCP_REQUEST is received, if a MAC to IP mapping exists already, the lease is renewed. This is renewed regardless of whether the lease is expired or not.