11th Lecture - Networking

[K.A.Paul]

[quote name='Alexander' timestamp='1318283063' post='2969465']
11k posts..
[/quote]

[k2s]

[quote name='Bondu_Babu' timestamp='1318283688' post='2969515']

teliste pm chey ba , ma room lo net disconnect cheyinchestha..................
[/quote]


these days every one is cautious....& knows about security.........they use atleast WEP ....... its tough to break the password.......
but atleast u can know how many types of passwords u can for securing ur network like...... WEP, WAP, WAP2 etc.....

[Bondu_Babu]

[quote name='k2s' timestamp='1318283839' post='2969526']


these days every one is cautious....& knows about security.........they use atleast WEP ....... its tough to break the password.......
but atleast u can know how many types of passwords u can for securing ur network like...... WEP, WAP, WAP2 etc.....
[/quote]

ne daggara material emaina vunte pm chey ba , nenu practice chesthanu........

[k2s]

[quote name='Bondu_Babu' timestamp='1318283931' post='2969533']

ne daggara material emaina vunte pm chey ba , nenu practice chesthanu........
[/quote]

material antu emi ledu.....cisco press books lo chadavatame.

[tom bhayya]

[quote name='Bondu_Babu' timestamp='1318283688' post='2969515']

teliste pm chey ba , ma room lo net disconnect cheyinchestha..................
[/quote]

[ToughGuy]

[quote name='k2s' timestamp='1318284038' post='2969545']

material antu emi ledu.....cisco press books lo chadavatame.
[/quote]

agreed

[k2s]

Ok..........guys,..... will start with last 10th lecture left out topic...

NAT = Network address translation

Let me know if u guys are not interested

[k2s]

Network Address Translation allows a single device, such as a router, to act as agent between the Internet (or ""public network"") and a local (or ""private"") network.

[k2s]

[b]The NAT router translates traffic coming into and leaving the private network:[/b]

[b][img]http://www.cisco.com/image/gif/paws/6450/nat-router.jpg[/img][/b]



The Internet has grown larger than anyone ever imagined it could be. Although the exact size is unknown, the current estimate is that there are about 100 million hosts and over 350 million users actively on the Internet. That is more than the entire population of the United States! In fact, the rate of growth has been such that the Internet is effectively doubling in size each year.
So what does the size of the Internet have to do with NAT? Everything! For a computer to communicate with other computers and Web servers on the Internet, it must have an [b]IP address[/b]. An IP address (IP stands for Internet Protocol) is a unique 32-bit number that identifies the location of your computer on a network. Basically it works just like your street address: a way to find out exactly where you are and deliver information to you.
When IP addressing first came out, everyone thought that there were plenty of addresses to cover any need. Theoretically, you could have 4,294,967,296 unique addresses (2[sup]32[/sup]). The actual number of available addresses is smaller (somewhere between 3.2 and 3.3 billion) because of the way that the addresses are separated into Classes and the need to set aside some of the addresses for multicasting, testing or other specific uses.

So IPv6 is our next step

[k2s]

Network Address Translation is used by a device (firewall, router or computer) that sits between an internal network and the rest of the world. NAT has many forms and can work in several ways:[list]
[*]
[b]Static NAT[/b] – Mapping an unregistered IP address to a registered IP address on a one-to-one basis. Particularly useful when a device needs to be accessible from outside the network.[b]In static NAT, the computer with the IP address of 192.168.32.10 will always translate to 213.18.123.110:[/b]
[/list]
[img]http://www.cisco.com/image/gif/paws/6450/nat-static.jpg[/img]

[k2s]

[b]Dynamic NAT[/b] – Maps an unregistered IP address to a registered IP address from a group of registered IP addresses. Dynamic NAT also establishes a one-to-one mapping between unregistered and registered IP address, but the mapping could vary depending on the registered address available in the pool, at the time of communication.
[b]In dynamic NAT, the computer with the IP address of 192.168.32.10 will translate to the first available address in the range from 213.18.123.100 to 213.18.123.150:[/b]

[img]http://www.cisco.com/image/gif/paws/6450/nat-dynamic.jpg[/img]

[k2s]

[b]Overloading[/b] – A form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address by using different ports. Known also as PAT (Port Address Translation), single address NAT or port-level multiplexed NAT.
[b]In overloading, each computer on the private network is translated to the same IP address (213.18.123.100) but with a different port number assignment:[/b]

[img]http://www.cisco.com/image/gif/paws/6450/nat-overload.jpg[/img]

[k2s]

[b]Overlapping[/b] – When the IP addresses used on your internal network are registered IP addresses in use on another network, the router must maintain a lookup table of these addresses so that it can intercept them and replace them with registered unique IP addresses. It is important to note that the NAT router must translate the "internal" addresses to registered unique addresses and also it must translate the "external" registered addresses to addresses that are unique to the private network. This can be done either through static NAT or you can use DNS and implement dynamic NAT.
[b]The internal IP range (237.16.32.xx) is also a registered range used by another network. Therefore, the router is translating the addresses to avoid a potential conflict with another network. It will also translate the registered global IP addresses back to the unregistered local IP addresses when information is sent to the internal network:[/b]

[img]http://www.cisco.com/image/gif/paws/6450/nat-overlap.jpg[/img]

[k2s]

see this flash: for better understanding.....

[url="http://www.cisco.com/image/gif/paws/6450/nat.swf"]http://www.cisco.com/image/gif/paws/6450/nat.swf[/url]

[k2s]

how to see the NAT table on a firewall

[color=#000000]

hostname# show xlate detail
[/color]


3 in use, 3 most used
Flags: D - DNS, d - dump, I - identity, i - inside, n - no random,
r - portmap, s - static
TCP PAT from inside:10.1.1.15/1026 to outside:192.150.49.1/1024 flags ri
UDP PAT from inside:10.1.1.15/1028 to outside:192.150.49.1/1024 flags ri
ICMP PAT from inside:10.1.1.15/21505 to outside:192.150.49.1/0 flags ri[color=#000000]



or

[color=#000000]

[b]hostname[/b]# [b]show xlate
[/b][/color]
Global 209.165.201.10 Local 209.165.201.10 static nconns 1 econns 0
Global 209.165.201.30 Local 209.165.201.30 static nconns 4 econns 0 [/color]