Posts Tagged ‘network’
July 22nd, 2008 | 
Author: ANDing: (Boolean and)
Computers use digital logic to interpret IP addresses
This logic is called a Boolean AND. It is the comparison of two bits to yield:
1 & 1 = 1
1 & 0 = 0
0 & 1 = 0
0 & 0 = 0
Any # ANDed with 0 is always 0
Any # ANDed with 1 is always the original #
The ANDing of an IP address & mask = network address
A subnet mask “masks” the host bits of an IP address
Routers and hosts use ANDing to determine networks
It is frequently necessary to be able to use ANDing
You will need to know how routers make routing decisions
Start with the IP address & mask above/below each other
10101100.00010000.00010100.00100011 172.16.24.35 (Host)
11111111.11111111.11111111.111 00000 255.255.255.224
——————————————————
10101100.00010000.00010100.00100000 172.16.23.32 (network address for
host /27)
Tags: vlan, ip, wan, cisco, study, switch
Grouping Devices into Networks and Hierarchical Addressing :
The original Internet – a few trusted users, no security issues.
Security needs have changed dramatically.
Dividing networks based on ownership means access can be prohibited, allowed, or monitored.
E.G. college network – admin, research, and student networks.
Security between networks is implemented in a router or firewall at the perimeter of the network.
The Internet = millions of hosts identified by a unique IP.
If each host had to know the address of all hosts it would severely degrade their performance.
Dividing networks so hosts who need to communicate are together reduces overhead (o/h) of hosts needing to know all IPs.
For all other destinations, hosts only need to know the address of a router.
This router is called a gateway. It serves as an exit from that network.
Hierarchical Addressing:
A hierarchical address uniquely identifies each host.
It also has levels that assist forwarding packets across internetworks, enabling division based on those levels.
So, hierarchical addressing supports communications between internetworks.
Postal addresses are examples of hierarchical addresses.
Refering only to the relevant address level (country, state, city, etc.) at each stage makes this process very efficient.
No need at each stage to know the all details (except Last).
IP addresses work in a similar way.
IP addresses have a network portion and a host portion.
Routers forward packets between networks using only the network portion.
Once delivered, the whole address will have been used to deliver the packet.
If necessary, additional layers of addressing can be created (subnet portion).
Tags: switch, interface, guides, vlan, ip, cisco