Command Promt commands

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TCP/IP Utilities

ipconfig (Windows OS)

ipconfig displays IP configuration information for network adapters. Use the ipconfig command as follows:

Use ipconfig to view IP adress, subnet mask, and default gateway configuration

Use ipconfig /all to view detailed configuration information including e MAC address and the DHCP server used for configuration

Use ipconfig /release to release the IP configuration information obtained from the DHCP server.

Use ipconfig /renew to request new IP configuration information from the DHCP server

Use ipconfig /displaydns and ipconfig /flushdns to view and manage the local DNS cache that Windows maintains and updates every 24 hours. The second option flushes (or removes) all the entries in the current DNS cache. If the IP address of a network server is changed, your local cache will contain the old IP address until the cache is updated or the flushdns option is used

ifconfig (Linux/Mac OS)

ifconfig is used on Linux and Mac OS systems and displays the installed network interfaces and the current configuration settings for each interface, including the MAC address, IP address, broadcast address, and subnet address. Use the ifconfig command as follows:

Use ifconfig [interface_name] down to disable the specified network interface

Use ifconfig [interface_name] up to enable specified network interface

Us the following utilities to display additional networking information not provided by ifconfig:

The hostname command displays the hostname of the system

The route command displays the default gateway configuration settings

On Linux systems, the iwconfig command is used to display information about wireless network interfaces.

ping

ping sends an ICMP echo request/reply packet to a remote host. A response from the remote host indicates that both hosts are correctly configured and a connection exists between them.

You can ping a host by IP address or use the DNS name. When the DNS name is used, the computer must look up the corresponding IP address before performing the ping test.

-a looks up the hostname from a given IP address

-t performs a continuous ping test (Press Ctrl + C to stop sending the ping tests)

-l [size] specifies the packet payload size (in bytes) to use in the test. This can help identify if packets above a certain size are being lost

tracert, traceroute

tracert is similar to the ping utility in that it tests connectivity between devices; however, tracert also shows the path between the two devices. Responses from each hop on the route are measured three times to provide an accurate representation of how long the packet takes to reach, and be returned by, the specific host.

On a Windows system, use the tracert command.

On Linux and Mac OS systems, use the traceroute command

nslookup

nslookup resolves (looks up) the IP address of the specified hostname. It also displays additional name resolution information, such as the DNS server used for the lookup request.

netstat

netstat displays the following IP-related statistics:

Current connections

Incoming and outgoing connections

Active sessions, ports, and sockets

The local routing table

nbtstat

nbtstat is used to diagnose issues regarding NetBIOS over TCP/IP. The following options can be used with nbtstat

-c displays the NetBIOS cache of remote machine names and their IP address

-n displays NetBIOS names that have been registered on the local system

-r displays names resolved by broadcast and via WINS

-R clears and then reloads the remote cache name table

-S Displays current NETBIOS sessions with the destination IP addresses

-s displays current NETBIOS sessions by NETBIOS names

Telnet

The telnet utility used for remote server management.

The Telnet protocol must be running and configured on the remote server in order for a Telnet session to be established

By default, Telnet does not encrypt transmissions (they are sent as clear text)

Telnet is mostly used by specialized industrial and scientific devices

In addition to sending transmissions in clear text, there are several well-known vulnerabilities in the Telnet protocol. Because of the, Telnet should not be used when sending sensitive information.

SSH

Similar to Telnet, the SSH utility is used for remote server management; however, SSH encrypts all communications and is much more secure.

SSH can be used to remotely log onto a server and complete configuration tasks

In order to establish an SSH session, the server must have the SSH process running and configured to allow remote connections

Use the following syntax to establishing an SSH connection:

ssh [username]@[server_address]