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Appendix A: Troubleshooting
Frequently Asked Questions
Wireless-G ADSL Home Gateway
What is the ISM band?
The FCC and their counterparts outside of the U.S. have set aside bandwidth for unlicensed use in the ISM
(Industrial, Scientific and Medical) band. Spectrum in the vicinity of 2.4 GHz, in particular, is being made available
worldwide. This presents a truly revolutionary opportunity to place convenient high-speed wireless capabilities in
the hands of users around the globe.
What is Spread Spectrum?
Spread Spectrum technology is a wideband radio frequency technique developed by the military for use in
reliable, secure, mission-critical communications systems. It is designed to trade off bandwidth efficiency for
reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband
transmission, but the trade-off produces a signal that is, in effect, louder and thus easier to detect, provided that
the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to
the right frequency, a spread-spectrum signal looks like background noise. There are two main alternatives,
Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).
What is DSSS? What is FHSS? And what are their differences?
Frequency-Hopping Spread-Spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern that
is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical
channel. To an unintended receiver, FHSS appears to be short-duration impulse noise. Direct-Sequence Spread-
Spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip
(or chipping code). The longer the chip, the greater the probability that the original data can be recovered. Even if
one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can
recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low
power wideband noise and is rejected (ignored) by most narrowband receivers.
Will the information be intercepted while it is being transmitted through the air?
WLAN features two-fold protection in security. On the hardware side, as with Direct Sequence Spread Spectrum
technology, it has the inherent security feature of scrambling. On the software side, WLAN offers the encryption
function (WEP) to enhance security and access control.
What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 64-bit or 128-bit shared key algorithm, as
described in the IEEE 802.11 standard.
What is a MAC Address?
The Media Access Control (MAC) address is a unique number assigned by the manufacturer to any Ethernet
networking device, such as a network adapter, that allows the network to identify it at the hardware level. For all
practical purposes, this number is usually permanent. Unlike IP addresses, which can change every time a
computer logs onto the network, the MAC address of a device stays the same, making it a valuable identifier for
the network.
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Appendix A: Troubleshooting
Frequently Asked Questions
Wireless-G ADSL Home Gateway
How do I reset the Gateway?
Press the Reset button on the back panel for about ten seconds. This will reset the Gateway to its default settings.
How do I resolve issues with signal loss?
There is no way to know the exact range of your wireless network without testing. Every obstacle placed between
the Gateway and a wireless computer will create signal loss.
Lead glass, metal, concrete floors, water and walls
will inhibit the signal and reduce range.
Start with the Gateway and your wireless computer in the same room
and move it away in small increments to determine the maximum range in your environment.
You may also try using different channels, as this may eliminate interference affecting only one channel.
I have excellent signal strength, but I cannot see my network.
WEP is probably enabled on the Gateway, but not on your wireless adapter (or vice versa).
Verify that the same
WEP keys and levels (64 or 128) are being used on all nodes of your wireless network.
How many channels/frequencies are available with the Gateway?
There are eleven available channels, ranging from 1 to 11, in North America. There may be additional channels
available in other regions, subject to the regulations of your region and/or country.
If your questions are not addressed here, refer to the Linksys international website,
www.linksys.com/international.
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Appendix B: Wireless Security
Security Precautions
Wireless-G ADSL Home Gateway
Appendix B: Wireless Security
Linksys wants to make wireless networking as safe and easy for you as possible. The current generation of
Linksys products provide several network security features, but they require specific action on your part for
implementation. So, keep the following in mind whenever you are setting up or using your wireless network.
Security Precautions
The following is a complete list of security precautions to take (at least steps 1 through 5 should be followed):
1.
Change the default SSID.
2.
Disable SSID Broadcast.
3.
Change the default password for the Administrator account.
4.
Enable MAC Address Filtering.
5.
Change the SSID periodically.
6.
Use the highest encryption algorithm possible. Use WPA if it is available. Please note that this may reduce
your network performance.
7.
Change the WEP encryption keys periodically.
For information on implementing these security features, refer to “Chapter 6: Configuring the Wireless-G ADSL
Home Gateway.”
Security Threats Facing Wireless Networks
Wireless networks are easy to find. Hackers know that in order to join a wireless network, wireless networking
products first listen for “beacon messages”. These messages can be easily decrypted and contain much of the
network’s information, such as the network’s SSID (Service Set Identifier). Here are the steps you can take:
Change the administrator’s password regularly.
With every wireless networking device you use, keep in
mind that network settings (SSID, WEP keys, etc.) are stored in its firmware. Your network administrator is the
only person who can change network settings. If a hacker gets a hold of the administrator’s password, he, too,
can change those settings. So, make it harder for a hacker to get that information. Change the administrator’s
password regularly.
NOTE:
Some of these security features are
available only through the network gateway,
router, or access point. Refer to the gateway,
router, or access point’s documentation for more
information.
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Appendix B: Wireless Security
Security Threats Facing Wireless Networks
Wireless-G ADSL Home Gateway
SSID.
There are several things to keep in mind about the SSID:
1.
Disable Broadcast
2.
Make it unique
3.
Change it often
Most wireless networking devices will give you the option of broadcasting the SSID. While this option may be
more convenient, it allows anyone to log into your wireless network. This includes hackers. So, don’t broadcast
the SSID.
Wireless networking products come with a default SSID set by the factory. (The Linksys default SSID is “linksys”.)
Hackers know these defaults and can check these against your network. Change your SSID to something unique
and not something related to your company or the networking products you use.
Change your SSID regularly so that any hackers who have gained access to your wireless network will have to
start from the beginning in trying to break in.
MAC Addresses.
Enable MAC Address filtering. MAC Address filtering will allow you to provide access to only
those wireless nodes with certain MAC Addresses. This makes it harder for a hacker to access your network with
a random MAC Address.
WEP Encryption.
Wired Equivalent Privacy (WEP) is often looked upon as a cure-all for wireless security
concerns. This is overstating WEP’s ability. Again, this can only provide enough security to make a hacker’s job
more difficult.
There are several ways that WEP can be maximized:
1.
Use the highest level of encryption possible
2.
Use “Shared Key” authentication
3.
Change your WEP key regularly
WPA.
Wi-Fi Protected Access (WPA) is the newest and best available standard in Wi-Fi security. Two modes are
available: Pre-Shared Key and RADIUS. Pre-Shared Key gives you a choice of two encryption methods: TKIP
(Temporal Key Integrity Protocol), which utilizes a stronger encryption method and incorporates Message
Integrity Code (MIC) to provide protection against hackers, and AES (Advanced Encryption System), which utilizes
a symmetric 128-Bit block data encryption. RADIUS (Remote Authentication Dial-In User Service) utilizes a
RADIUS server for authentication and the use of dynamic TKIP, AES, or WEP.
IMPORTANT:
Always remember that each
device in your wireless network MUST use
the same encryption method and encryption
key or your wireless network will not function
properly.
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Appendix B: Wireless Security
Security Threats Facing Wireless Networks
Wireless-G ADSL Home Gateway
WPA Pre-Shared Key
. If you do not have a RADIUS server, Select the type of algorithm, TKIP or AES, enter a
password in the Pre-Shared key field of 8-64 characters, and enter a Group Key Renewal period time
between 0 and 99,999 seconds, which instructs the Gateway or other device how often it should change the
encryption keys.
WPA RADIUS
. WPA used in coordination with a RADIUS server. (This should only be used when a RADIUS
server is connected to the Gateway or other device.) First, select the type of WPA algorithm,
TKIP
or
AES
.
Enter the RADIUS server’s IP Address and port number, along with a key shared between the device and the
server. Last, enter a Group Key Renewal period, which instructs the device how often it should change the
encryption keys.
RADIUS
. WEP used in coordination with a RADIUS server. (This should only be used when a RADIUS server is
connected to the Gateway or other device.) First, enter the RADIUS server’s IP Address and port number, along
with a key shared between the device and the server. Then, select a WEP key and a level of WEP encryption,
and either generate a WEP key through the Passphrase or enter the WEP key manually.
Implementing encryption may have a negative impact on your network’s performance, but if you are transmitting
sensitive data over your network, encryption should be used.
These security recommendations should help keep your mind at ease while you are enjoying the most flexible
and convenient technology Linksys has to offer.

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