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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).

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Tags: switch, interface, guides, vlan, ip, cisco

IP Addressing Structure:
IPv4 Address = 32 bit # written as dotted decimals
Always paired with a 32 bit mask
Computers evaluate &
E.G. 10101000 <- high-order that side, -> low order this side.

Network = group of hosts with identical network addresses.
Some portion of the low-order bits = host address.
From our 32 bits, the # of bits used in the host portion determines how many hosts we can have in our network.
E.G. if 200 hosts in our network. We need enough bits in the host portion to make 200+ numbers
2^7 = 128, 2^8 = 256, therefore 8 bits minimum are required to get 200+ hosts.

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Tags: vlan, cisco, switch, ip, router, wan

OSI Transport Layer:

Transport Layer

Accepts data from Application layer and prepares it for layer 3;
Responsible for end to end transfer of data.
Enables multiple applications to communicate simultaneously.
Ensures data received reliably and in order.
Employs error handling mechanisms.

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Tags: cisco, 802.1q, guides, router, vlan, ip

Application – Interface Between Human and Data

Applications generate most network traffic.

Application layer:

Provides the interface between Applications and underlying networks;
Contain many different protocols:

TCP/IP

Predates the OSI model;
Application layer equal to the top 3 layers of OSI Layers;
Implements little functionality at Pressentation and Session layers.

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Tags: ip, cisco, router, study, wan, vtp