IP static and DHCP problem

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Wireless Router Network Diagram	Ethernet Router Network Diagram	Hybrid Ethernet Router / Wireless Access Point Network Diagram	Direct Connection Network Diagram
Ad Hoc Wireless Network Diagram	Ethernet Hub/Switch Network Diagram	Phoneline Home Network Diagram	Powerline Home Network Diagram
Two Router Home Network Diagram

How To Identify Network Hardware IP Addresses on a Local Network
1 - IP Address Notation,
2 - IP Address Classes, Broadcast and Multicast,
3 - IP Loopback and Private Addresses, IPv6 Anycast,
4 - DNS - Domain Name System,
5 - IP Network Numbering,
6 - Subnet Masks and Subnetting

7 - IP Subnetting in Practice,
8 - CIDR - Classess Internet Domain Routing,
9 - IP Practice Test

IP Address of a Router

A typical home network router possesses two IP addresses, one for the internal home (LAN) and one for the external Internet (WAN) connection.

The internal, LAN-IP address is normally set to a default, private number. Linksys routers, for example, use 192.168.1.1 for their internal IP address. D-Link and Netgear routers typically use 192.168.0.1. Some US Robotics routers use 192.168.123.254, and some SMC routers use 192.168.2.1. No matter the brand of router, its default internal IP address is listed in the manufacturer's documentation. Administrators have the option to change this IP address during router setup or at any time later. Unless someone manually changes it, however, this private LAN-IP address remains fixed. This address can be viewed and changed from the router's administrative console.

The external, WAN-IP address of the router is set when the router connects to the Internet service provider. This address can also be viewed on the router's administrative console. Alternatively, the WAN-IP address can be found by visiting a Web-based IP address lookup service like http://checkip.dyndns.org/ from any computer on the home LAN.

Another way to identify the public IP addresses of routers, involves executing a ping or traceroute command. From inside a home network, the (DOS) command "ping -r 1" will send a message through the home router that will cause its IP address to be displayed. For example, "ping -r 1 www.yahoo.com" should result in a message like the following displayed on the command prompt:

Reply from 66.94.230.43: bytes=32 time=294ms TTL=56
Route: 209.179.21.76
...

In this example, the IP address after "Route:" (209.179.21.76) corresponds to the router WAN address.

On corporate networks, network discovery services based on SNMP can automatically determine the IP addresses of routers and many other network devices. 

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Static IP address assignment (sometimes also called fixed addressing) is an alternative to dynamic addressing (normally, DHCP) on Internet Protocol networks. Dynamic addressing is convenient. It also allows mobile computers to more easily move between different networks.

However, static IP addressing also offers some advantages:

• A static IP address best supports name resolution, so that a computer can be most reliably reached over the network by its host / domain name. Web and FTP servers in particular benefit from fixed addressing for this reason.
  
  
• Using static IP addresses on home networks gives somewhat better protection against network security problems than does DHCP address assignment.
  
  
• Some network devices do not support DHCP. Using static IP address assignment for all devices on the home network guarantees to avoid potential address conflicts where DHCP may supply an address already assigned statically elsewhere.

When using static IP addresses on home and other private networks, they should be chosen from within the standard private IP address ranges listed:

• 10.0.0.0 through 10.255.255.255
• 172.16.0.0 through 172.31.255.255
• 192.168.0.0 through 192.168.255.255

These ranges support many thousands of different IP addresses. It's common for people to assume that any address in these ranges can be chosen and the specific choice doesn't matter much. This is untrue. To choose and set specific static IP addresses suitable for your network, follow these guidelines.

1. Do not choose any addresses that end with ".0" or ".255" - these addresses are generally reserved for use by network protocols.
   
   
2. Do not choose the addresses at the beginning of a private range. IP addresses like 10.0.0.1 and 192.168.0.1 are very commonly used by network routers and other consumer devices. These are the first addresses someone will attack when trying to break into a private computer network.
   
   
3. Do not choose an address that falls outside the range of your network mask. For example, to support all addresses in the 10.x.x.x private range, the network mask on all devices must be set to 255.0.0.0, otherwise some static IP addresses in this range will not work.