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wireles network hacks mods - briere D.

briere D. wireles network hacks mods - Wiley publishing, 2005. - 387 p.
ISBN: 0-7645-9583-0
Download (direct link): wirelesnetworkhacks.pdf
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^ The default gateway handles the routing of packets going to another network.
^ A Domain Name Servers server (DNS server) is used to map the hierar-chal host names to IP address so packets can be correctly addressed and routed.
TCP/IP addresses
An IPv4 address is composed of four bytes, each of which has 8 bits and is called an octet. An example address is 140.88.76.21.
The decimal value of a byte can range from 0 to 255, which is the range of the values an octet can represent. Each octet is separated with a period and, depending upon the subnet mask used, you can break an IP address into a network and a host ID.
The subnet mask
The subnet mask is required for all IP configurations. Unlike the IP address, the mask address ranges from the largest number first. A subnet mask is often composed of either values of 255 or 0, although other values such as 24, 36, 92, 240, or 224 can be used. An example is 255.255.255.0.
Its appearance is different than the IP address and other parameters because it really isn’t an address. Instead, it’s a way to interpret IP addresses. Technically, a subnet mask defines bits that are used to compare the local IP address with the address of a node the local host wants to communicate with. The purpose of this comparison is to determine whether the other host is on the same local network.
Chapter 5: Combining Wired and Wireless Networks
Gateway
The default gateway specifies the address of the router connected to the local network. This router provides a path for packets destined for other networks. Packets destined for hosts on the local network can be sent directly to the host through the local network switch. Packets for remote hosts have the remote address included, but are sent directly to the router so it can determine the proper path to deliver them.
DNS
The DNS address specifies the IP address of the DNS server. The DNS server has a database that indexes computer names and IP addresses. When a user specifies a computer name, such as a Web site in a browser like www.digital dummies.com, DNS automatically resolves that name to an IP address so that communications can continue.
Private subnets
Three IP network address ranges are reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These addresses can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a Network Address Translation (NAT) device, proxy server, or a router that provides NAT. Using these devices is always safe because routers on the Internet never forward packets coming from these addresses. This also means that these addresses cannot be used to access the Internet without some routable address attached to one of the devices listed above.
The 192.168.x.x address is by far the most common. As you spend more time playing around with home networking gear, you will find this reserved range of class C addresses used as the default for most home networking equipment.
Figure 5-1 shows a private subnet in action.
Subnetting an IP network can be done for a variety of reasons, including organization, use of different physical media (such as Ethernet, FDDI, WAN connection — like DSL or cable — and so on), preservation of address space, and security. The most common reason, from an ISP’s perspective, is to control network traffic. From a corporation’s perspective, the most common reason is to preserve address space.
In the end, it doesn’t matter why your network has to be subnetted, just that it does.
Part II: Boosting Performance on Your Wireless Network
sexy
Public network 10.1.1.0/24
Interface public address 10.1.1.12 netmask 255.255.255.0
Interface local address 192.168.0.254 netmask 255.255.255.0
Figure 5-1:
Private
subnets
Workstation
192.168.0.1
Laptop
192.168.0.2
Server
192.168.0.17
Someday in the not-so-distant future, ISPs will move from today’s version of IP (IPv4) to a new version called IPv6. IPv6 supports more IP addresses than today’s system does — orders-of-magnitude more — so that every networkable device in the world (even if every person had thousands of such devices) can have a unique IP address. When this happens (and it will be years from now when it does), NAT will be unnecessary — all of the devices on your home network will be full peers on the Internet.
One advantage of NAT is that it provides a bit of firewall-like protection. Because computers out on the Internet cannot directly connect to your 192.168.xxx.xxx IP-addressed devices, hacking your networked equipment is a bit harder for the people using those computers. The NAT router is a bit picky about which traffic it lets through the Internet connection and onto your network, so that helps reduce hacking. Considering a router that goes beyond just NAT and also includes an SPI (stateful packet inspection) firewall is still sensible, however: It actually digs into the data packets hitting your Internet connection to help filter out the bad guys doing bad things.
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