Transparent Bridging

Transparent bridges are devices which connects more than one network segments with other bridges to make all routing decisions.Transparent bridges are sometimes called learning bridges. When they are turned on and receive data packets from a network segment they:
- Learn the relation between MAC address and segment/port, and
- Forward the packet to all other segments/ports.

There are two types of Transparent Bridge Modes:
- Store-and-Forward: Stores the entire frame and verifies the CRC before forwarding the frame. If a CRC error is detected, the frame is discarded.
- Cut-Through: Forwards the frame just after it reads the destination MAC address without performing a CRC check.

Transparent bridges are so named because their presence and operation are transparent to network hosts. When transparent bridges are powered on, they learn the workstation locations by analyzing the source address of incoming frames from all attached networks.

How Transparent Bridging Operates ?
The bridge uses its table as the basis for traffic forwarding. When a frame is received on one of the bridge’s interfaces, the bridge looks up the frame’s destination address in its internal table. If the table contains an association between the destination address and any of the bridge’s ports aside from the one
on which the frame was received, the frame is forwarded out the indicated port. If no association is found, the frame is flooded to all ports except the inbound port. Broadcasts and multi casts also are flooded in this way.
Transparent bridges successfully isolate intra-segment traffic, thereby reducing the traffic seen on each individual segment. This is called filtering and occurs when the source and destination MAC addresses reside on the same bridge interface.

Benefits of Transparent Bridging :
Transparent bridging can deliver many benefits including more efficient usage of finite network resources, improved responsiveness, reduced wait delays, fewer network errors resulting from collisions, plug ‘n’ play installation capabilities, reduced administrative managed requirements and overheads, superior network bandwidth allocation, reduced instances of the deleterious effects of broadcast storms, loop and redundancy issues.

Network Bridging

Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on flooding and examination of source addresses in received packet headers to locate unknown devices. Once a device has been located, its location is recorded in a table where the MAC address is stored so as to preclude the need for further broadcasting. The utility of bridging is limited by its dependence on flooding, and is thus only used in local area networks.
A network bridge is a device which connects two parts of a network together at the data link layer (layer 2 of the OSI model).

Situations Where Bridging Is Appropriate :
- Connecting Networks.
- Filtering/Traffic Shaping Firewall.
- Network Tap.
- Layer 2 VPN : Two Ethernet networks can be joined across an IP link by bridging the networks to an EtherIP tunnel or a tap(4) based solution such as OpenVPN.
- Layer 2 Redundancy : A network can be connected together with multiple links and use the Spanning Tree Protocol to block redundant paths.

Advantages :
- Self-configuring.
- Isolate collision domain.
- Reduce the size of collision domain by micro segmentation in non-switched networks.
- Transparent to protocols above the MAC layer.
- LANs interconnected are separate, and physical constraints such as number of stations, repeaters and segment length don't apply.
- Helps minimize bandwidth usage.

Disadvantages :
- It does not limit the scope of broadcasts.
- It does not scale to extremely large networks.
- Buffering and processing introduces delays.
- Bridges are more expensive than repeaters or hubs.

Bridges - Basic Hardware Component

A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges inspect incoming traffic and decide whether to forward or discard it. Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.

Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Today, bridges are slowly but surely falling out of favor. Ethernet switches offer similar functionality; they can provide logical divisions, or segments, in the network. In fact, switches are sometimes referred to as multi-port bridges because of the way they operate.

Network Interface Cards (NIC)

A Network Interface Card (NIC) provides the hardware interface between a computer and a network. A NIC technically is network adapter hardware in the form factor of an add-in card. Networked computers communicate with each other using a given protocol or agreed-upon language for transmitting data packets between the different machines, known as nodes. The network interface card acts as the liaison for the machine to both send and receive data on the LAN.
Some NIC cards work with wired connections while others are wireless. Most NICs support either wired Ethernet or WiFi wireless standards. In new computers, many NICs are now pre-installed by the manufacturer. NICs can be differentiated by their type of connectivity to the computer itself.

- 10/100 Ethernet : These cards are networking cards that are used most frequently in the home or small office setting. They are capable of speeds up to 10 or 100 megabits per second.
- Gigabit Ethernet :These NICs provide network transfer speeds of up to one Gigabit per second.
- Fiber Optics : These NICs use fiber optic cabling to reach speeds of 10 gigabits per second currently, with a specification under review to push this limit to 100 gigabits per second.
- Wireless NICs : These NICs provide the same networking capabilities as their wired counterparts, however, they have their own transfer capabilities. Speeds of 54 Mb/s are the most commonly available to wireless NICs without teaming several NICs together to combine bandwidths.
- Wireless Dongles : There is a wireless networking device used by individual machines that have access to a main computer that is connected to a wireless router. This wireless router allows the user to install wireless dongles instead of entire routers with each additional machine on the network.

Bus Network Topology

A bus network is an arrangement in a local area network (LAN) in which each node (workstation or other device) is connected to a main cable or link called the bus. Bus networks are the simplest way to connect multiple clients, but may have problems when two clients want to transmit at the same time on the same bus. A true bus network is passive – the computers on the bus simply listen for a signal; they are not responsible for moving the signal along.
The bus topology makes the addition of new devices straightforward. The term used to describe clients is station or workstation in this type of network. Bus network topology uses a broadcast channel which means that all attached stations can hear every transmission and all stations have equal priority in using the network to transmit data.



Advantages :
* Easy to implement and extend.
* Well-suited for temporary or small networks not requiring high speeds (quick setup).
* Cheaper than other topologies.
* Cost effective; only a single cable is used.
* Easy identification of cable faults.
* Reduced weight due to fewer wires.

Disadvantages :
* Limited cable length and number of stations.
* If there is a problem with the cable, the entire network goes down.
* Maintenance costs may be higher in the long run.
* Performance degrades as additional computers are added or on heavy traffic.
* Proper termination is required.
* Significant Capacitive Load.
* It works best with limited number of nodes.
* It is slower than the other topologies.

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (effectively either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network we use the Token Ring technology. A Token is passed from one computer to another which enables each computer to have equal access to the network.
Because a ring topology provides only one pathway between any two nodes, ring networks may be disrupted by the failure of a single link. A node failure or cable break might isolate every node attached to the ring. Each packet is sent around the ring until it reaches its final destination. Today, the ring topology is seldom used.



Advantages of Ring Network :
* Very orderly network where every device has access to the token and the opportunity to transmit.
* Performs better than a star topology under heavy network load.
* Can create much larger network using Token Ring.
* Does not require network server to manage the connectivity between the computers.

Disadvantages of Ring Network :
* One malfunctioning workstation can create problems for the entire network.
* Moves, adds and changes of devices can affect the network.
* Much slower than an Ethernet network under normal load.

Star Network Topology

Star Topology is the most common type of network topology that is used in homes and offices. In the Star Topology there is a central connection point called the hub which is a computer hub or sometimes just a switch.
In local area networks where the star topology is used, each machine is connected to a central hub. In contrast to the bus topology, the star topology allows each machine on the network to have a point to point connection to the central hub. All of the traffic which transverses the network passes through the central hub.



Advantages of Star Topology :
- A Star Network Topology is very easy to manage because of its simplicity in functionality.
- The problems can be easily located logically in a Star Topology and therefore is easy to troubleshoot also.
- The Star Topology is very simple in format so it is very easy to expand on the Star Topology.

Disadvantages of Star Topology :
- The Star Topology is fully dependent on the hub and the entire working of the network depends on the hub or the switch.
- If there are many nodes and the cable is long then the network may slow down.

Extended Star Network :
A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node and the peripheral or 'spoke' nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes.

Distributed Star Topology :
A type of network topology that is composed of individual networks that are based upon the physical star topology connected together in a linear fashion – i.e., 'daisy-chained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or 'spokes').