What is a MAC address?

A MAC address is a physical hardware address assigned to each device that has the capability of connecting to a network. The internet is nothing more than a large network. The MAC address is something that is assigned in the chip on the device and is not something the user can change.

- JMD COMPUTER INDIA

Source:http://www.whatismyip.com/faq/what-is-a-mac-address.asp

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UNIX IP Commands

Display Current Config for all NIC's: ifconfig

Display Current Config for dc0: ifconfig dc0

Assign multiple IP's: ifconfig dc0:0 192.168.1.2

Assign second IP: ifconfig dc0:1 192.168.1.3

Disable network card: ifconfig dc0 down

Enable network card: ifconfig dc0 up

Assign IP/Subnet: ifconfig dc0 inet 192.168.1.2 netmask 255.255.255.0

Assign Gateway: route delete default && route add default 192.168.1.1

You MUST be at the ROOT user to make/save any changes. You will need to save your changes in the /etc/rc.conf file. Network cards are referred to as dc0, dc1, dc2, etc based on their position on the PCI bus.

Special thanks to Romanov Sergey Vladimirovich from Moscow for the UNIX command.

- JMD COMPUTER INDIA

Source: http://www.whatismyip.com/faq/unix-ip-commands.asp

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Linux IP Commands

Display Current Config for all NIC's: ifconfig

Display Current Config for eth0: ifconfig eth0

Assign IP: ifconfig eth0 192.168.1.2

Ping: ping -c 3 192.168.1.1

Assign multiple IP's: ifconfig eth0:0 192.168.1.2

Assign second IP: ifconfig eth0:1 192.168.1.3

Disable network card: ifconfig eth0 down

Enable network card: ifconfig eth0 up

View current routing table: route "or" route -n

View arp cache: arp "or" arp -n

Assign IP/Subnet: ifconfig eth0 192.168.1.2 netmask 255.255.255.0

Assign Default Gateway: route add default gw 192.168.1.1

Trace Route: traceroute www.whatismyip.com

Trace Path: tracepath www.whatismyip.com

DNS Test: host www.whatismyip.com

Advanced DNS Test: dig www.whatismyip.com

Reverse Lookup: host 66.11.119.69

Advanced Reverse Lookup: dig -x 66.11.119.69

You MUST be at the ROOT user to make/save any changes. Linux users, your distribution will determine the location of your network config file which will need to be updated and saved in order for the changes to remain in effect after rebooting. Network cards are referred to as eth0, eth1, eth2, etc based on their position on the PCI bus.

Special thanks to Gergely for the Linux commands!

- JMD COMPUTER INDIA

Source: http://www.whatismyip.com/faq/linux-ip-commands.asp

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DOS / Windows IP Commands

Display Connection Configuration: ipconfig /all

Display DNS Cache Info: ipconfig /displaydns

Clear DNS Cache: ipconfig /flushdns

Release All IP Address Connections: ipconfig /release

Renew All IP Address Connections: ipconfig /renew

Re-Register the DNS connections: ipconfig /registerdns

Change/Modify DHCP Class ID: ipconfig /setclassid

Network Connections: control netconnections

Network Setup Wizard: netsetup.cpl

Test Connectivity: ping www.whatismyip.com

Trace IP address Route: tracert

Displays the TCP/IP protocol sessions: netstat

Display Local Route: route

Display Resolved MAC Addresses: arp

Display Name of Computer Currently on: hostname

Display DHCP Class Information: ipconfig /showclassid

- JMD COMPUTER INDIA

Source: http://www.whatismyip.com/faq/dos-windows-ip-commands.asp

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What Is DHCP?

Dynamic Host Configuration Protocol

In simple terms, DHCP determines if your IP is static or dynamic.

DHCP is controlled by a DHCP server. Your router can be a DHCP server...and if you're on a home network, it most likely is your DHCP server.

I know this might be confusing because the word dynamic is in the term, but just because you have DHCP enabled on your computer doesn't mean you can't be assigned a static IP. DHCP enabled on your computer simply means you're letting a DHCP server assign its IP. Having it enabled DOES NOT mean it's a DHCP server.

A true DHCP server (not your Linksys router) gives the LAN Admin a ton of control with IP assigning.

Ever print to a network printer? Ever wonder how that printer keeps its network assignment? Probably through DHCP. Each network device has a MAC address. You can assign a static IP at the DHCP server to a specific MAC address. This allows the network printer to always get the same IP even after it reboots and without assigning the IP at the printer. If you print the network configuration at the printer, it will probably tell you that DHCP is enabled and no static IP is assigned. That's because the IP assignment is handled at the DHCP server.

Your ISP has a DHCP server. They can assign IPs by modem MAC addresses. When your modem comes online, it communicates to the network indicating it is looking for an IP address. The DHCP server listens to this communication and starts talking to the modem. The modem then transmits its MAC address to the DHCP server. At that point, either an IP has been reserved for the modem or one is assigned at that time. Hence cloning your MAC address to get a new IP from your ISP.

Routers and DHCP - Under the General Setup or LAN Setup tab in your router, you'll see a settings option for DHCP. You can control how many IPs are assigned or to enable/disable the DHCP server portion of the router. If you disable it, you'll have to statically assign IPs to each computer, or have a DHCP server or your network. This goes for wired and wireless. Any connection on your network has an IP address.

There's a lot more to DHCP than this, but this is a basic explanation.

- JMD Computer India

Source:- http://www.whatismyip.com/faq/what-is-dhcp.asp

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