Sunday, March 15, 2020

Switch Overview & Configrations

Switch Overview & Configrations

A network switch is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. 

Saturday, March 14, 2020

Spanning Tree Protocol(STP)


Don’t confuse Spanning Tree Protocol (STP) with Shielded Twisted Pair (STP).

Spanning Tree Protocol - 1

Ethernet bridges and switches can implement the IEEE 802.1D Spanning-Tree Protocol and use the spanning-tree algorithm to construct a loop free shortest path network.

Shortest path is based on cumulative link costs.
Link costs are based on the speed of the link.

Spanning Tree Protocol - 2 

The Spanning-Tree Protocol establishes a

root node, called the root bridge/switch.

The Spanning-Tree Protocol constructs a topology that has one path for reaching every network node. The resulting tree originates from the root bridge/switch.

The Spanning-Tree Protocol requires network devices to exchange messages to detect bridging loops. Links that will cause a loop are put into a blocking state.

The message that a switch sends, allowing the formation of a loop free logical topology, is called a Bridge Protocol Data Unit (BPDU).

Selecting the Root Bridge

The first decision that all switches in the network make, is to identify the root bridge. The position of the root bridge in a network will affect the traffic flow.

When a switch is turned on, the spanning-tree algorithm is used to identify the root bridge. BPDUs are sent out with the Bridge ID (BID).

The BID consists of a bridge priority that defaults to 32768 and the switch base MAC address.

When a switch first starts up, it assumes it is the root switch and sends BPDUs. These BPDUs contain the switch MAC address in both the root and sender BID. As a switch receives a BPDU with a lower root BID it replaces that in the BPDUs that are sent out. All bridges see these and decide that the bridge with the smallest BID value will be the root bridge.

A network administrator may want to influence the decision by setting the switch priority to a smaller value than the default.


BPDUs contain enough information so that all switches can do the following:
Select a single switch that will act as the root of the spanning tree
Calculate the shortest path from itself to the root switch • Designate one of the switches as the closest one to the
root, for each LAN segment. This bridge is called the “designated switch”. The designated switch handles all communication from that LAN towards the root bridge.
Each non-root switch choose one of its ports as its root port, this is the interface that gives the best path to the root switch.
Select ports that are part of the spanning tree, the designated ports. Non-designated ports are blocked.

Spanning Tree Port States

Spanning Tree Operation

When the network has stabilized, it has converged and there is one spanning tree per network. As a result, for every switched network the following elements exist:
One root bridge per network
One root port per non root bridge • One designated port per segment • Unused, non-designated ports
Root ports and designated ports are used for forwarding (F) data traffic. Non-designated ports discard data traffic.
Non-designated ports are called blocking (B) or discarding ports.

Spanning Tree Port States
Spanning Tree Recalculation

A switched internetwork has converged when all the switch and bridge ports are in either the forwarding or blocked state.

Forwarding ports send and receive data traffic and BPDUs.

Blocked ports will only receive BPDUs.

When the network topology changes, switches and bridges recompute the Spanning Tree and cause a disruption of user traffic.

Convergence on a new spanning-tree topology using the IEEE 802.1D standard can take up to 50 seconds.

This convergence is made up of the max-age of 20 seconds, plus the listening forward delay of 15 seconds, and the learning forward delay of 15 seconds.

Tuesday, March 3, 2020



1.     Unplug the power cable of Cisco switch.
2.     Press the "mode" button over Cisco switch.
3.     Re-power the device.
4.     Release the "mode" button after approximately 15-20 seconds. "switch: prompt:" should appear.
5.     Type "dir flash:" command.
6.     Type "rename flash:config.text flash:config.old"  ( config.text is the file in your flash )
7.     Type "boot"
8.     Go to enable mode and type "rename flash:config.old flash:config.text"
9.     Type "rename flash:config.old flash:config.text"
10. Type "copy flash:config.text system:running-config"
11. Give your new passwords,  type "write memory" and reload and that is all !

Saturday, February 8, 2020

DCN - Application Layer Introduction

The application layer is the highest layer in the OSI and TCP / IP layer model. This layer is found in both models in layers due to its importance, for interacting with the user and user applications. This layer is intended for applications participating in the communication system.

The user may or may not interact directly with the applications. The application layer is where real communication begins and is reflected. Because this layer is at the top of the layer stack, it does not serve any other layer. The application layer takes Transport instructions and all the layers below to connect your data or transfer it to the remote host.

When the application layer protocol wants to communicate with its peer application layer protocol on a remote host, it delivers data or information to the transport layer. The transport layer does the rest with all the layers beneath it.

There is ambiguity in understanding the application layer and its protocol. Not all user apps can be placed in the application layer. Except for those applications that interact with the communication system. For example, program design or text editor cannot be considered application layer programs.

On the other hand, when we use a web browser, we actually use Hypertext Transfer Protocol (HTTP) to interact with the network. HTTP is the application layer protocol.

Another example is File Transfer Protocol, which helps the user to transfer text or binary files over the network. User can use this protocol in graphical user interface-based programs like FileZilla or CuteFTP and the same user can use FTP in command line mode.

Therefore, no matter which program you use, it is the protocol that is considered in the application layer used by this program. DNS is a protocol that helps a user’s application protocols, such as HTTP, to function.

Friday, December 6, 2019


The fiber distributed data interface (FDDI), which is a standard for optical data communication used in long distance networks, provides connection to fiber optic lines up to 200 kilometers at a speed of 100 megabits per second (Mbps) .

The fiber distributed data interface is standard for transferring data on a local network. The optical fibers are used as the standard primary physical medium, although it is then determined that they use copper cables, in which case they can be called CDDI, standardized as TP-PMD and also called TP-DDI.

FDDI is used as the main pillar to connect copper LAN as shown in the figure. The FDDI cable consists of two fibrous rings, one of them clockwise and the other counterclockwise. A set of ANSI protocols to send digital data through a fiber optic cable. FDDI networks are token pass networks and support data rates of 100 Mbps (100 million bits) per second. FDDI networks are generally used as the basis for broadband networks.

Although the FDDI logical structure is a ring-based token network, it did not use the IEEE 802.5 token loop protocol as the basis for it; instead, its protocol was derived from the IEEE 802.4 token bus protocol.


WiMAX (global microwave interoperability) is a set of wireless broadband standards based on the IEEE 802.16 set of standards, which provides multiple physical layer (PHY) and media access control (MAC) options.

According to some estimates, the cost of existing subscriber equipment is around $ 300, almost double the price of WiFi devices, cables and DSL customer service. On the platform, it is estimated that it will take a total of $ 3 billion to establish a national WiMAX network in the United States.

Wi-Fi generally provides access to the local network for a few hundred feet at speeds of up to 54 Mbps, and a single WiMAX antenna range is expected to reach 40 miles at speeds of 70 Mbps or more. As such, WiMAX can provide the basic Internet connection necessary to service local Wi-Fi networks.

The WiMAX architecture developed by the WiMAX model support is a unified network architecture to support fixed, nomadic and mobile operations. Communication service network, CSN: This part of the WiMAX network provides IP connectivity and all the main functions of the IP network.

Static WiMAX works in the 2.5 GHz and 3.5 GHz frequency bands, which require a license, in addition to the 5.8 GHz frequency band without a license. WiMAX Portable, also called IEEE 802.16e, allows the client's mobile devices to connect to the Internet.


The Layer Two Tunnel Protocol (L2TP) is a tunnel protocol that is used to support virtual private networks (VPNs) or as part of the provision of services by Internet service providers. It does not provide any encryption or confidentiality in itself.

The Layer Two Tunnel Protocol (L2TP) protocol is designed on all modern operating systems and devices that support VPN. ... alone, L2TP does not provide any encryption or confidentiality for the traffic it is going through, so it is generally applied using an IPsec Authentication Kit (L2TP / IPsec).

L2TP generally uses the authentication protocol, IPSec (Internet Protocol Security). Use strong encryption and documentation. IPSec gives you a final advantage over some of the most commonly used protocols such as PPTP. The protocol uses UDP ports 1701. L2TP is the VPN protocol that does not provide encryption or protection against traffic passing through the connection. For this reason, it is usually combined with IPSec, which is an encryption protocol.

Layer Two Tunneling Protocol (L2TP) is a computer network protocol that the ISP uses to enable virtual private network (VPN) operations. L2TP is similar to the data link layer protocol in the OSI reference model, but in reality it is a session layer protocol.

Star LAN

A star topology is a local area network (LAN) topology in which all nodes are individually connected to a central connection point, such as a hub or switch. The star takes more than one cable as a bus, but the benefit is that if a cable fails, only one node will fall.

A local network can operate as a few or two users (for example, in a small office network) or several hundred users in a larger office. LANs consist of cables, switches, routers and other components that allow users to connect to internal servers, websites and other local networks through broadband networks.

Asterisk is an application of the hub distribution model in computer networks. In the stellar network, each host is connected to a central hub. In its simplest form, a central hub acts as a channel for transmitting messages. The stellar network is one of the most common computer network topologies.

A stellar network is a local area network (LAN) where all nodes (workstations or other devices) are connected directly to a shared central computer. Each workstation is indirectly connected to each other through the mainframe. In some star networks, the central computer can also act as a workstation.