Building a Home
Network
Kent Reuber
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
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.
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.
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
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.
QuickTime™ and a
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”
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.
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.
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.
QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture.
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!
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
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
Example home network:
mixed public/NAT setup
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
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
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.
QuickTime™ and a
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.
QuickTime™ and a
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
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
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
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…
QuickTime™ and a
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.
QuickTime™ and a
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.
Kent’s Stanford DSL
Network
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
Books
“
Linksys Networks, the
Official Guide
”, Kathy Ivens,
Larry Seltzer, Osborne
“
Home Networking Bible
”,
Web Sites
Stanford West/Welch Rd.
Computing FAQ:
http://www.stanford.edu/services/sta
nfordwest/faq.html
Stanford VPN Service:
http://vpn.stanford.edu
Stanford DSL Service:
