Router

Router (computing):
A router is a networking device, commonly specialized hardware, that forwards data packets between computer networks. This creates an overlay inter network, as a router is connected to two or more data lines from different networks. When a data packet comes in one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the inter network until it reaches its destination node.

The most familiar type of routers are home and small office routers that simply pass data, such as web pages, email, IM, and videos between the home computers and the Internet. An example of a router would be the owner's cable or DSL router, which connects to the Internet through an ISP. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.

Routing is often confused with bridging, which performs a similar function. The principal difference between the two is that bridging occurs at a lower level and is therefore more of a hardware function whereas routing occurs at a higher level where the software component is more important. And because routing occurs at a higher level, it can perform more complex analysis to determine the optimal path for the packet.

Types of Routing Protocols 

Table 3-1 showed how routing protocols can be classified according to various characteristics. This section gives an overview of the most common IP routing protocols. Most of these routing protocols will be examined in detail in other chapters. For now, this section gives a very brief overview of each protocol.

Classifying Routing Protocols 

Routing protocols can be classified into different groups according to their characteristics. Specifically, routing protocols can be classified by their:

Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)
Operation: Distance vector protocol, link-state protocol, or path-vector protocol
Behavior: Classful (legacy) or classless protocol
For example, IPv4 routing protocols are classified as follows:

RIPv1 (legacy): IGP, distance vector, classful protocol
IGRP (legacy): IGP, distance vector, classful protocol developed by Cisco (deprecated from 12.2 IOS and later)
RIPv2: IGP, distance vector, classless protocol
EIGRP: IGP, distance vector, classless protocol developed by Cisco
OSPF: IGP, link-state, classless protocol
IS-IS: IGP, link-state, classless protocol
BGP: EGP, path-vector, classless protocol

The data networks that we use in our everyday lives to learn, play, and work range from small, local networks to large, global inter networks. At home, a user may have a router and two or more computers. At work, an organization may have multiple routers and switches servicing the data communication needs of hundreds or even thousands of PCs.

Routers forward packets by using information in the routing table. Routes to remote networks can be learned by the router in two ways: static routes and dynamic routes.

In a large network with numerous networks and subnets , configuring and maintaining static routes between these networks requires a great deal of administrative and operational overhead. This operational overhead is especially cumbersome when changes to the network occur, such as a down link or implementing a new subnet. Implementing dynamic routing protocols can ease the burden of configuration and maintenance tasks and give the network scalability.

This introduces dynamic routing protocols. It explores the benefits of using dynamic routing protocols, how different routing protocols are classified, and the metrics routing protocols use to determine the best path for network traffic. Other topics covered in this chapter include the characteristics of dynamic routing protocols and how the various routing protocols differ. Network professionals must understand the different routing protocols available in order to make informed decisions about when to use static or dynamic routing. They also need to know which dynamic routing protocol is most appropriate in a particular network environment.

What is a Motherboard?

The motherboard serves to connect all of the parts of a computer together. The CPU, memory, hard drives, optical drives, video card, sound card and other ports and expansion cards all connect to the motherboard directly or via cables.

The motherboard is the piece of computer hardware that can be thought of as the "back bone" of the PC.

The Motherboard is Also Known As:

mainboard, mobo (abbreviation), MB (abbreviation), system board, logic board

Important Motherboard Facts:

• Desktop motherboards, cases and power supplies all come in different sizes called form factors. All three must be compatible to work properly together.
• Motherboards vary greatly in respect to the types of components they support. For example, each motherboard supports a single type of CPU and a short list of memory types. Additionally, some video cards, hard drives and other peripherals may not be compatible. The motherboard manufacturer should provide clear guidance on component compatibilities.
•  In laptops and tablets, and increasingly even in desktops, the motherboard often incorporates the functions of the video card and sound card. This helps keep these types of computers small in size.
• In a desktop, the motherboard is mounted inside the case, opposite the most easily accessible side. It is securely attached via small screws through pre-drilled holes.
• The front of the motherboard contains ports that all of the internal components connect to. A single socket/slot houses the CPU. Multiple slots allow for one or more memory modules to be attached. Other ports reside on the motherboard which allow the hard drive and optical drive (and floppy drive if present) to connect via data cables.
• Small wires from the front of the computer case connect to the motherboard to allow the power, reset and LED lights to function. Power from the power supply is delivered to the motherboard by use of a specially designed port.
• Also on the front of the motherboard are a number of peripheral card slots. These slots are where most video cards, sound cards and other expansion cards are connected to the motherboard.
• On the left side of the motherboard (the side that faces the back end of the desktop case) are a number of ports. These ports allow most of the computer's external peripherals to connect such as the monitor, keyboard, mouse, speakers, network cable and more.
• All modern motherboards also include USB ports here, and increasingly other ports like HDMI and FireWire, that allow compatible devices to connect to your computer when you need them - devices like digital cameras, printers, etc.
• The desktop motherboard and case are designed so that when peripheral cards are used, the sides of the cards fit just outside the back end, making their ports available for use.

Ethernet Network Card Installation:

Typically an Ethernet network interface is built-in to most modern motherboards. Some computer systems, especially server systems, are equipped with two network interfaces built-in to the motherboard. Additional interfaces can be installed in extra PCI expansion slots.

Try the command lspci -vv to see if the hardware is detected properly, and which kernel module (if any) is being assigned:

01:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5764M Gigabit Ethernet PCIe (rev 10)
    Subsystem: Hewlett-Packard Company Device 1309
    Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0, Cache Line Size: 64 bytes
    Interrupt: pin A routed to IRQ 52
    Region 0: Memory at f7000000 (64-bit, non-prefetchable) [size=64K]
    Capabilities: <access denied>
    Kernel driver in use: tg3
    Kernel modules: tg3


...
...

37:09.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5782 Gigabit Ethernet (rev 03)
    Subsystem: Hewlett-Packard Company Device 000c
    Physical Slot: 5
    Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
    Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 32 (16000ns min), Cache Line Size: 64 bytes
    Interrupt: pin A routed to IRQ 21
    Region 0: Memory at f8000000 (64-bit, non-prefetchable) [size=64K]
    [virtual] Expansion ROM at f7100000 [disabled] [size=64K]
    Capabilities: <access denied>
    Kernel driver in use: tg3
    Kernel modules: tg3

or more specifically lspci -vv | grep Ethernet

01:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5764M Gigabit Ethernet PCIe (rev 10)
37:09.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5782 Gigabit Ethernet (rev 03)

NS2 Scenario Generator

If you are tired of writing code using .tcl files, here is a solution for that. This software is a little bit old, as it released sometime during 2007, still some of the students/Researchers are not aware of this software.
So, you need not waste your time in editing the tcl files. And since this software is written in java, it works well with almost any Operating System (With JRE installed on the System)

You can download the software from this link https://sites.google.com/site/pengjungwu/nsg
Some features of this software

1. wired and wireless nodes will be created
   
2. establish connection between the nodes
3. Creating links (Duplex-Link and Simplex-Link)
4. TCP and UDP agents are supported
5. Creating applications (CBR and FTP)
6. Node movement

And still there are lot more as the developer of this software is actively maintaining the software and you can expect lot more in the future also.

The Network Simulator ns-2:

Scenario Generation

In order to carry out meaningful study of different networking issues like protocol interaction, congestion control, effect of network dynamics, scalability etc it is necesssary to carry simulations on the right kind of scenario which includes but is not limited to the topology size, density distribution, traffic generation, membership distribution, real-time variance of membership, network dynamics etc. Different scenarios can be used to illustrate/compare interesting network performances.

Scenario Generator

The ns scenario generator can be used to create different random scenarios for simulation. It consists of a topology generator, an agent generator and a routing generator that are each described below. The scenario generator is available in a zipped format consisting of Tcl scripts that can be run with ns-2. Example scripts are provided for each type of generator.

Topology Generator: The topology generator can generate topology using any standard graph generator (GT-ITM, Tiers etc). Currently it supports GT-ITM generator only and converts the topology graph into ns format. See the example script topo-gen-script.tcl for details on different topology options. For more help , run ns, source topo-gen.tcl and type "topology -h". You can also use "topo-usage" or "detailed-topo-usage" commands at ns prompt as shown below:
your_prompt%ns
%source topo-gen.tcl
%topology -h
or
%topo-usage
%topo-usage: topology [options]

where options are given as: -key value
example options:
-outfile mytopo -type random -nodes 50 -method pure-random
[.....]
%detailed-topo-usage
usage: topology [-key 1 value 1 -key 2 value 2 -key n value n]
[...]

Agent Generator: The agent generator can be used to define transport protocol agents like TCP or SRM, type of sources to be used by transport agents, different traffic models for sources, location/distribution of endpoints across the topology, a start time range within which different agents start randomly, multicast-tree membership dynamics etc. Again take a look at example script agent-gen-script.tcl for details. For more help you can use "agents -h" or "agent-usage" or "detailed-agent-usage" at ns prompt after having sourced agent-gen.tcl.

Route Generator: The routing generator defines the routing protocols to be used in the simulation. The options include unicast routing, multicast routing and an option to turn on/off the expand address flag (when turned on the address space is increased from default size of 16 to 32 bits setting 1 bit for mcast, 21 bits for nodeid and 8 bits for portid). For more help type "routing -h" after sourcing route-gen.tcl or use command "route-usage" to give detailed info for routing options.