Building a Home Network

1. Building a Home Network Kent Reuber reuber@stanford.edu

2. Outline • Will focus on physical layouts. Hard to get very specific. • Too many OS versions and network hardware combinations. • Example network layouts. • Example home network components.

3. General recommendations • Buying things: • Ask questions (e.g., Expert Partners list) before you buy. Have a goal… • Check online to see if manuals are available. • Buy stuff that you can return, if possible. • Use dedicated hardware (e.g., print servers, broadband routers) rather than software • Dedicated hardware is more robust and simpler to operate. • Don’t have to depend on a computer being up.

4. Networking shopping list • Necessary or highly recommended: • Internet Service Provider (ISP). • Broadband (NAT) router. • Print server or network printer. • Cables. • Optional: • Wireless access point. • Wireless repeater. • Small hubs/switches. • Web cams, …

5. Network addressing • All IP addresses within the network must be unique. • Check your docs for subnet mask and gateway. • Most broadband routers have DHCP servers, so you don’t have to manage addresses manually. “All I did was to ask for her IP address.” (IT Guy comic)

6. Broadband routers

7. Broadband (NAT) router • Hides network from the outside world using NAT. • Connections: • WAN Ethernet interface for connection to ISP equipment. • Ethernet LAN interface(s). • Usually also has wireless.

8. What is NAT? • NAT = “Net Address Translation” • Several different methods. For the gory details, see RFC 1613. • Most frequently encountered method is the one used in home broadband routers which “hide” an entire non-routable network range behind a single routable “public” IP address. • Ref: Bill Dutcher: “The NAT Handbook” (Wiley)

9. Why would you want to use NAT? • Allows you to buy a single IP address from your ISP and share that address among a large number of devices. (May save $$) • All devices on the local network can access the Internet at the same time, though the bandwidth is shared. • Firewall: • Outside hosts can *reply* to hosts behind the NAT router. • Inside hosts have to initiate the connection. • Note: there are some ways around this.

10. NAT router setup • NAT routers are given two IP’s addresses: • 1 non-routable (LAN -- you) • 1 routable (WAN – ISP) • Machines on LAN side get special non-routable addresses (usually 10.*.*.* or 192.168.*.*). • No IP addresses in these ranges are routed on the Internet.

11. How NAT works • Normal routers maintain source and destination IP addresses from end-to-end. • NAT routers change IP addresses and port. • Outgoing packets appear to come from the NAT router’s public address. • NAT routers keep track of each “flow” so that replies can be returned.

12. How NAT firewalling works • Suppose a host (either friendly or malicious) sends a packet to the NAT router without the connection being initiated from the inside. • Outside hosts can’t send directly to the hosts on the local network side -- they have non-routable addresses! • Since there is no entry in the flow table, the NAT router has no idea where to forward it and drops the packet. Instant firewall!

13. Circumventing the NAT firewall (if you must) • You may want to run a server behind your NAT router. How do you let in some traffic? • NAT routers have a limited ability to “port forward”, sending all traffic to a given computer on the internal net and bypassing the flow table. • For example: • Send all Web traffic (port 80) to 192.168.1.3 • Send all mail traffic (port 25) to 192.168.1.5 • You can get hacked if forwarded port is running a vulnerable service! For example, if your IIS Web server isn’t patched, your firewall won’t help you. Always keep services with open ports patched.

14. Should you use a NAT router? • It’s your only choice if you get 1 address from your ISP and you want to create a network. • If you get multiple addresses from your ISP, you don’t necessarily need one, but it’s still a good idea. • Examples: Stanford DSL, Stanford West, Welch Rd. apartments. • May want to put one or more hosts on the public side of the NAT (e.g., file server). • You should keep most private information (e.g., bank accounts) on the private side.

15. Example home network: mixed public/NAT setup

16. Wireless

17. Wireless frequency choices • Usually you’ll want wireless 802.11b/g support. • My opinion: wait on 802.11n until the standard is more mature. • Internet access speed is usually limited by the ISP. • Most DSL is only 1 Mbps. Even 802.11b won’t be a bottleneck. • Faster 802.11g usually only matters for transfers within your network.

18. Wireless network name • A computer will be able to roam freely between access points with the same network name (also called SSID) • Any of your access points should have a different SSID than those of your neighbors. • In most cases, all of your access points should broadcast the same SSID. • If you put up your own wireless on campus, it should not use the SSID “Stanford”. Use a name that indicates that it belongs to you.

19. Wireless protection • Use address filters, WEP or WPA to prevent neighbors from using your wireless. • May want to use hidden SSID (network name). • Use encrypted protocols (https, SSH, Kerberos, SSL) especially in public wireless areas.

20. Printing and cabling

21. Print server • Used to network a printer that doesn’t have a network interface. • Usually has one Ethernet and one or more parallel or USB interfaces. • Wireless also available.

22. Cables • Ethernet cables • Category 5 or 5e is sufficient. No need for Category 6. • Only 2 pair cable is necessary for 10/100. Gigabit needs 4 pairs. • May need crossover cables for switch-switch connections. • May also need USB or parallel cables.

23. Other devices

24. Wireless access point • Wireless broadband router without the router. • Usually only 1 Ethernet port. • Use if you need more than one wireless for coverage. • Also useful if your broadband router doesn’t have wireless. • Range extenders are also available.

25. Hubs and switches • Probably doesn’t matter which you use. Unlikely that your net is so congested that a switch would add performance. • Switch speed is almost always faster than your ISP, so switch speed will not be a bottleneck to accessing the Internet. • Always remember not to create loops in cabling -- you must wire in a “star” shape.

26. Web cams • Many of the new Internet cameras have built-in Web servers so that you don’t need a computer. • Some people use cams for security or just to watch their kittens…

27. Voice over IP (VoIP) • Many companies are starting to sell equipment that can place calls over Internet connections. • Expect lower quality voice, but you may save money.

28. Stanford-run networks

29. Stanford DSL • 5 usable Stanford IP addresses. • Network is ready to go. • Can access resources IP limited resources (e.g., journals) • Don’t need a broadband router, but it’s still a good idea. • Netopia router (provided): • Can distribute your addresses via DHCP. Good for laptops. • Has 4 10/100 ports for devices. • Only routes IP. • DNS is provided by campus servers. • You can connect to your computer by specifying its hostname (xxx.stanford.edu).

30. Kent’s Stanford DSL Network

31. Stanford West/Welch Rd. • 10Mbit Ethernet service. Not DSL! • Way faster than DSL. 100Mbit service available. • Up to 4 Stanford IP address for each paid jack. Can also get additional private (non-routable) addresses for print-servers, access points, etc. • Like department Ethernet networks, any network protocol that gets sent onto the wire can affect your neighbors. Play nice! • DHCP & DNS provided by campus servers.

32. Books • “Linksys Networks, the Official Guide”, Kathy Ivens, Larry Seltzer, Osborne • “Home Networking Bible”, Sue Plumley, Wiley

33. Web Sites • Stanford West/Welch Rd. Computing FAQ: • http://www.stanford.edu/services/stanfordwest/faq.html • Stanford VPN Service: • http://vpn.stanford.edu • Stanford DSL Service: • http://www.stanford.edu/services/dsl/