Routes, Interfaces, DNS, ARP, etc...

This section describes the misc. stuff involved in networking. XOK supports multiple ethernet interfaces and exopc comes with the typical ifconfig, route etc tools along with an arp demon and DNS resolver.

• Interfaces: During boot up, the kernel initializes the network cards, and the sysinfo structure. The sysinfo structure contains the number of slow and fast ethernet cards that the kernel recognized.

  The IP address of the machine will be determined by the first process. This process then proceeds to initialize a global interface table that contains basic ``ifconfig'' information, like physical interface number, ip address, ethernet address (cached from sysinfo), netmask and flags. Programs use this information to know if an IP address is on the local LAN or remote; if it is on a remote location, then they look in the route table for the route.

• ARP: The first process spawns an arp daemon. There is a global arp_table mapped into each process. Only the arp daemon can write to this table. Processes check the arp table to find a translation IP->ether. If not found, they ipc into the arp daemon to add the entry, and block until the status of the entry changes. The arp daemon will retransmit the arp request until it gets a reply or times out. The arp daemon also responds to arp requests from other machines in the network. There are basically two functions user-level programs need to know about:
  • arp_resolve_ip(ipaddress,ethaddress for result, interface)
  • arp_remove_ip(ipaddress)
• Routes: The route procedures are used to find out which is the proper interface for the ipaddress. All process have a route table that is in shared memory. Each process can read and write into this table. The first process sets the routes by default. The ``route'' program can also be used for this purpose. It is important to set the routes early on, as most libos code uses this to locate which interface to use. More information as well as interface definitions can be found in the source.
• DNS:

  ExOS uses the same routines used in OpenBSD. You just have to make sure that all the networking code is ready by the time you need to resolve your first address.