B-2: TCP/IP Settings Problems
Ethernet LAN
ADSL/Cable/
V.90/ISDN
Modem
Default Gateway
of WIASA
Ethernet/
RS232
WIASA
IEEE 802.11b
Stage A
State B
Stage C
Correspondent
Host
Stage D
Client
Computer
DNS Server
of WIASA
Phone/
CATV
Network
Internet
Fig. 53. Communication stages for a client to reach its correspondent host.
For a client computer to communicate with a correspondent host on the Internet by the host’s 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 WIASA, then the WIASA relays this request to the default gateway of
the WIASA through a modem. 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 fol-
lowing a reverse path. When the client computer receives the DNS reply, it knows the IP address of
the correspondent host and sends further packets to this IP address.
As illustrated in Fig. 53, 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 commu-
nication 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-provided
Device
Manager
to disable unnecessary NICs.
Solve the following problems in order:
The WIASA does not respond to
ping
from the client computer.
Are two or more NICs installed on the client computer?
Use the OS-provided command-line network tool,
route.exe
, to modify the contents
of the routing table.
Use Windows
-
provided
Device Manager
to disable unnecessary NICs.
Is the underlying link (Ethernet or IEEE 802.11b) established?
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