User-mode Linux

• way of running a whole operating system as a process on another.
• original purpose: operating system debugging.
• side-effect: a great way to learn to play with systems.

Our network:

Tualatin: "bastion host"

• Must log into it before one can get to host01-host29
• On two networks with differing Ethernet addresses.
• Does not pass packets from one network to the other.

Host01-Host29: private network

• Subnet: 10.10.118.0/24 = 10.10.118.1 to 10.10.118.254.
• Broadcast address: 10.10.118.255.
• RFC1918: permanently private address space; will never have direct access to Internet.

uml_switch

• a program running on host01-host29.
• simulates a switched environment between your UML program and the network.
• It's as if your linux were an extra node in this network (behind tualatin).
• br0: bridge device. Used by uml_switch to maintain the illusion that all hosts and all UML instances are bridged into one subnet.

Imperfections

• A normal linux's network device is eth0, not br0.
• Sometimes, uml_switch hangs (especially if you try to run two uml instances with the same IP address) and has to be restarted.
• Sometimes, it's necessary to reboot the host in order to fix UML.
• Very slow: every packet has to be "switched" between UML and the real network in software.
• (By comparison, the competitor commercial program "VMWare" is very fast, it directly connects linux to the ethernet device. But it's $)

Defining our network

• Name server: tualatin
  • Answers requests for name-to-address mapping.
  • Use "nslookup" or "dig" to test it out.
  • See tualatin:/var/named/
• Dynamic Host Configuration Protocol (DHCP) server: tualatin
  • when host01-host29 boot, they ask tualatin for their ip address assignments.
  • See tualatin:/etc/dhcpd.conf

The whole EECS network:

• Two hops between ECE/CS and Tufts
  • Network Address Translation box: translates private internal addresses into public external addresses for outgoing requests.
• Packet filters on main router determine what kinds of traffic can be routed.
• Internal network is multihomed: several subnets on "one wire":
  • 130.64.23.0/24: traditionally, Suns and Linux.
  • 130.64.24.0/24: traditionally, Windows and Mac.
  • 10.3.0.0/16: private stations