User's Manual

20
B-2: TCP/IP Settings Problems
Default Gateway
of Client Computer
AP
IEEE 802.11b
Stage A
State B
Correspondent
Host
Stage D
Client
Computer
DNS Server
of Client Computer
Ethernet LAN
Internet
Fig. 20. Communication stages for a client to reach its correspondent host.
For a wireless client computer to communicate with a correspondent host on the Internet by the hosts
domain name (e.g. http://www.wi-fi.com), it first sends a DNS request to a DNS server on the Internet.
The DNS request travels first to the AP, then the AP relays this request to the default gateway of the
client computer. Finally, this request is forwarded by the gateway to the DNS server on the Internet.
The DNS reply issued by the DNS server is transmitted back to the client computer following a rever-
se path. When the client computer receives the DNS reply, it knows the IP address of the correspon-
dent host and sends further packets to this IP address.
As illustrated in Fig. 20, the communication path could be broken at some of the stages. The OS-
provided network diagnostic tool, ping.exe, can be employed to find out TCP/IP-related communica-
tion problems.
NOTE: If two or more NICs are installed and operating on a client computer, TCP/IP may not work
properly due to incorrect entries in the routing table. Use the OS-provided command-line network tool,
route.exe, to add or delete entries from the routing table. Or, use Windows Device Manager to dis-
able unnecessary NICs.
Solve the following problems in order:
l The AP does not respond to ping from the client computer.
n Are two or more NICs installed on the client computer?
u Use the OS-provided command-line network tool, route.exe, to modify the contents
of the routing table.
u Use Windows Device Manager to disable unnecessary NICs.
n Is the underlying link (Ethernet or IEEE 802.11b) established?