Understanding Wireless LAN Routers

By definition, a router transfers packets between networks. The router chooses
the next best link to send packets on in order to reach closer to the destination.
Routers use Internet Protocol (IP) packet headers and routing tables, as well
as internal protocols to determine the best path for each packet. Most routers
connect a LAN (like the one in your home or office) to a WAN (like the cable
system running your cable modem) by interfacing a broadband modem to the network
within the enterprise, small office, or home.

A wireless LAN router adds a built-in access point function to a multi-port
Ethernet router. This combines multiple Ethernet networks with wireless connections
as well. A typical WLAN router includes four Ethernet ports, an 802.11 access
point, and sometimes a parallel port so it can be a print server. This gives
wireless users the same ability as wired users to send and receive packets over
multiple networks. 802.11b, 802.11a, and 802.11b/a combo WLAN routers are now
available from several vendors such as Netgear, D-Link
and Actiontec. 802.11g routers are also
starting to come on the market.

WLAN Routers vs. Access Points

There may be some confusion over the difference between WLAN routers and access
points. The main thing to remember is that access points allow wireless clients
access to a single network, while WLAN routers allow clients to browse a number
of different networks. The router always takes the IP address into account to
make decisions on how to forward (i.e., route) the packet; whereas, access points
generally ignore the IP address and forward all packets.

In addition, WLAN routers implement the Network Address Translation
(NAT) protocol that enables multiple network devices to share a single IP address
generally provided by the Internet Service provider (ISP). WLAN routers also
have the ability to provide port-based control, firewall management and Dynamic
Host Configuration Protocol
(DHCP) services for all devices. These functions
make the WLAN router much more versatile than an access point.

Why use a WLAN router?

Consider using a WLAN router for the following reasons:

  • IP address sharing. WLAN routers offer strong benefits in the home
    and small office setting. For example, you can subscribe to a cable modem
    service that provides a single IP address through DHCP to the router, and
    the router then provides IP addresses via DHCP to clients on your local network.
    NAT then maps a particular client on the local network to the ISP-assigned
    IP address whenever that client needs to access the Internet. As a result,
    you need a router if you plan to have more than one networked devices on a
    local network sharing a single ISP-assigned address. Instead of having one
    box for the router and another box for the access point, a WLAN router provides
    both in the same box.
  • Connect multiple networks. WLAN routers are also ideal for wireless
    networks in public areas, especially if there are multiple networks that are
    accessible. For instance, a University may have a separate network in each
    of its buildings. Students sitting outside might want to gain access one or
    more of these networks and also surf the Internet. A WLAN router enables them
    to access everything through the wireless connection.
  • Improve network management. WLAN routers in an enterprise environment
    give network administrators an extra way to monitor and update their networks.
    In addition to being able to log on either locally or remotely via the wired
    network, they will be able to log on wirelessly and make any observations
    or changes.
  • Improve network performance. Because routers only send packets to
    specific, directed addresses, they do not forward the often numerous broadcast
    packets that are sent out by other devices. This results in an increase in
    throughput because of lower utilization on the network and less work needed
    by the router. This enables WLANs to operate much more effectively. The router,
    however, will offer more delay than an access point, but the impacts are generally
    unnoticeable.
  • Increase security. A strong advantage of WLAN routers is that they
    provide an added layer of security, both on the wired side and wireless side.
    The wired side is usually protected by a firewall and has extensive access
    control filters. These filters can be set based on MAC (medium access control)
    address, IP address, URL, domain name, and even a set schedule that allows
    access only at certain times. If an unauthorized user tries to access the
    network, an e-mail alert is immediately sent to the network administrator.
    For supporting sensitive information, many WLAN routers support multiple and
    concurrent IPSec sessions,
    so users can more securely access networks through a range of virtual private
    network (VPN) clients. Most WLAN routers also implement wired equivalent
    privacy
    (WEP) encryption.

Configuring a WLAN Router

Most WLAN routers are easy to install and configure. Physically connecting
the unit to a broadband modem or hub is made easier through clearly written
instructions, labeled ports and illustrations.

When installing a WLAN router, consider the following:

  • Identify the IP address and domain server address for the WAN (broadband
    connection) side of the router. You will need to configure the router with
    these addresses. In some cases, the ISP provides these addresses through DHCP.
    In this case, you’ll need to activate DHCP for the router’s WAN port.
  • Define IP addresses for the local side of the router. In most cases, especially
    with wireless networks, DCHP is the best way to assign addresses to client
    devices on the local network (wireless and wired LAN side of the router).
    As a result, configure the router to assign these addresses via DHCP. Assign
    a starting and maximum number of addresses that you want DHCP to assign. Be
    sure to include all network devices. This includes potential PDAs and printers
    in addition to PCs and laptops that may access the network.
  • Configure 802.11 parameters on the access point. This includes the service
    set identifier (SSID), WEP, radio frequency
    channel
    , transmit power and other functions such as request-to-send
    / clear-to-send
    (RTS / CTS) and fragmentation.
    Be sure to set the SSID and administrative login user name / password to a
    non-default value to improve
    security
    . For single access point networks, you can probably use the default
    radio channel, but another channel might be needed to avoid conflicting with
    other nearby access points. In most cases, set the transmit power to the highest
    value (usually the default setting). Other settings will depend on application
    requirements.

A WLAN router is certainly a component to consider for any Wi-Fi deployments.
It pulls together the routing and access point functions into a single component
that is relatively easy to configure and manage. When deploying WLANs, however,
also consider the use of bridges and
repeaters.

Jim Geier provides independent consulting services to companies
developing and deploying wireless network solutions. He is the author of the
book, Wireless LANs (SAMs,
2001).

Join Jim for discussions as he answers questions in the 802.11 Planet Forums.

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