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Hack 53 Troubleshooting Network Connections with netsh, netstat, and ipconfig

More command-line tools for tracking down
problems with your network connection.

In addition to well-known command-line network utilities such as
ping,
tracert,
and pathping,
there are several other all-purpose utilities that can help you
troubleshoot network connections: netsh,
netstat, and ipconfig.

5.13.1 Use netsh to Troubleshoot Network and Internet Connections

netsh is a wide-ranging command-line
diagnostic tool that has an exceedingly large number of commands
available. (For a complete list of available commands, use Windows XP
Help and Support and search for netsh.) Here
you'll learn the most interesting.

Perhaps the most useful of the netsh commands are
the netsh diag commands. Use them to find out
information about your PC's network setup, such as
finding the IP address of its mail server, newsgroup server, DNS
server, and similar resources.

There are two ways to use
netsh: directly from the command line
with all its switches, or first getting to the
netsh console by typing netsh
at the command line and then typing the command from the
netsh> prompt that appears. For example, you
could type netsh diag show adapter at the command
line, which lists every network adapter on your PC, or you could get
to the netsh> prompt and type diag
show adapter.

Use the netsh command to connect to the resources
and then get information about them. For example, to find out the


IP address of your DNS
servers, type netsh diag show dns; to find out the
IP address of your mail server, type netsh diag connect
mail.

Table 5-7 list the most useful of the
netsh
diag commands. Precede each of them with netsh
diag. Note that they each have many switches associated
with them. For more details, use Windows XP Help and Support and
search for netsh.

5.13.2 Use netstat to Get Information About Open Network Connections

If you
want to get a snapshot of all incoming and outgoing network
connections, use the netstat command. At a command
prompt, type netstat. It lists all connections,
including the protocol being used, the local and Internet addresses,
and the current state of the connection, like this:

Active Connections
Proto  Local Address       Foreign Address        State
TCP    PrestonGralla:1031  localhost:2929         ESTABLISHED
TCP    PrestonGralla:2887  192.168.1.103:netbios-ssn  TIME_WAIT
TCP    PrestonGralla:2899  www.oreillynet.com:http  ESTABLISHED
TCP    PrestonGralla:2900  www.oreillynet.com:http  ESTABLISHED
TCP    PrestonGralla:2932  mail.attbi.com:pop3    ESTABLISHED
TCP    PrestonGralla:2936  vmms2.verisignmail.com:pop3  ESTABLISHED

It will help you know whether connections are live, the network or
Internet device to which they're connected, and
which local resource is making the connection. It's
best suited for when you're troubleshooting network
problems and want to find out whether certain ports are open, why
certain computers on the network are having connection problems, and
similar issues. You can use command-line switches with
netstat. For example, display open ports and open
connections with this syntax: netstat
-a. Table 5-8 lists
netstat switches.

-a

-e

-n

-o

-p proto

-r

-s

interval value

5.13.3 Use IPConfig to Troubleshoot TCP/IP

One of the most powerful tools
for analyzing and troubleshooting TCP/IP problems is the
ipconfig command-line utility. It provides
information about each of your adapters, including
the assigned IP address, subnet mask, default gateway,


MAC address, DNS servers, whether

DHCP is enabled, and a
variety of other data. To see basic information about your adapters,
type ipconfig at a command prompt, and
you'll see information like this:

Windows IP Configuration
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix  . : ne1.client2.attbi.com
IP Address. . . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1
PPP adapter {6A724E76-AB59-4ABC-BBF5-41CA4410EB8D}:
Connection-specific DNS Suffix  . :
IP Address. . . . . . . . . . . . : 172.165.155.106
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . :

As you can see, ipconfig provides basic
information about your IP address, subnet mask, default gateway, and
a connection-specific DNS suffix, if any. However, you can get much
more detailed information by using the /all
switch, like this: ipconfig /all. For most
troubleshooting purposes, use the /all switch. You
get a much more comprehensive listing, as shown here:

Windows IP Configuration
Host Name . . . . . . . . . . . . : PrestonGralla
Primary Dns Suffix  . . . . . . . :
Node Type . . . . . . . . . . . . : Hybrid
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix  . : ne1.client2.attbi.com
Description . . . . . . . . . . . : CNet PRO200WL PCI Fast Ethernet Adapter
Physical Address. . . . . . . . . : 00-08-A1-00-9F-32
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 192.168.1.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . . . . : 192.168.1.1
DNS Servers . . . . . . . . . . . : 204.127.202.19
216.148.227.79
Lease Obtained. . . . . . . . . . : Saturday, December 28, 2002 8:53:40 AM
Lease Expires . . . . . . . . . . : Sunday, December 29, 2002 8:53:40 AM
PPP adapter {6A724E76-AB59-4ABC-BBF5-41CA4410EB8D}:
Connection-specific DNS Suffix  . :
Description . . . . . . . . . . . : WAN (PPP/SLIP) Interface
Physical Address. . . . . . . . . : 00-53-45-00-00-00
Dhcp Enabled. . . . . . . . . . . : No
IP Address. . . . . . . . . . . . : 172.165.155.106
Subnet Mask . . . . . . . . . . . : 255.255.255.255
Default Gateway . . . . . . . . . :
DNS Servers . . . . . . . . . . . : 64.12.104.134
NetBIOS over Tcpip. . . . . . . . : Disabled

You can also use ipconfig
to release and renew IP addresses, and perform other
troubleshooting functions as well. For example, to renew an
adapter's IP address, use this command:

ipconfig /renew "adapter name"

where adapter name is the name of the
adapter whose IP address you want to renew. Make sure to put quotes
around the adapter name and use spaces if there is more than one word
in the adapter name. Table 5-9 lists other
switches you can use with ipconfig.

/all

/displaydns

/flushdns

/registerdns

/release "adapter"

/renew "adapter"

/setclassid "adapter" newclassid

/showclassid "adapter"