Thursday, August 14, 2014

Spanning Tree Protocol

Spanning Tree Protocol

Redundant Topology
A Local Area Network may consist of more than one segment. Each segment of the LAN connected through a separate physical device mostly switch. Switches use their uplink ports to connect different segments. The LAN administrator can connect the switches with each other through more than one uplink port using redundant topology. Redundant topology eliminates the single point of failure and that will improve the performance of network. Overall redundant topology is a good solution for making a LAN efficient but there are some drawbacks of redundant topology. It causes broadcast storms, multiple frame copies and MAC address table instability problems. For example there are two switches connect with each other using redundant topology. A host on one segment sends a broadcast frame. Broadcast frames are flooded to all ports other than the originating port. Remembering redundant topology, there are two uplink ports are using on both the switches, so the switches continue to propagate the broadcast traffic over and over through the uplink ports. Complex topology can cause multiple loops to occur and layer 2 has no mechanism to stop the loops. The solution is Spanning Tree Protocol.
Spanning Tree Protocol Basics
The IEEE defines the Spanning Tree Protocol that provides a loop free redundant network topology by placing certain ports in the blocking state. STP works in a broadcast domain therefore each VLAN has its own spanning tree. Spantree 1 is by default enabled in the Cisco switches for the default VLAN 1. A switch as compare to bridge may have multiple spanning tree protocols as the number of VLAN while Inter VLAN routing supports ip spanning.
How Spanning Tree Protocol Works
The spanning-tree operations are as follows:
  • STP elects a Root Bridge and both the ports of the Root Bridge are designated ports and are placed in the forwarding state.
  • The non Root Bridge considers one of its ports as a root port with the least administrative cost and the other port considers as a non designated port. Root port placed in the forwarding state in the blocking state while the non designated port is in the blocking state. Spanning Tree Protocol Algorithm
    The STP algorithm selects the Root Bridge first:
  • Root Bridge is the switch with the lowest Bridge ID and Bridge ID consists of bridge priority and MAC address. The lowest bridge priority chosen first, the default bridge priority value is 32768; if the bridge priority is same then the lowest MAC address will be chosen.
  • Messages are sent to each switch through BPDU frame. The Bridge Protocol Data Unit (BPDU) frame is also called Hello. By default, Hello messages are sent after every 2 seconds.
  • If a switch receives BPDU that is lowest then its self, the switch forwards that BPDU, claiming it to be the root port.
  • Cost is calculated by adding the cost in the received BPDU to the cost of the interface the BPDU was received. How STP Handles the Network Topology Changes?
  • Hello time: The time root waits before sending periodic Hello BPDU that are forwarded by the other switches. By default, it is 2 seconds.
  • Max Age: The time any switch should wait before trying to change the STP topology after unhearing Hello BPDU.
  • Forward Delay: The delay time an interface takes to converge from blocking state to forwarding state. STP Operation Summary
  • The root sends hello BPDU frame out of all interfaces.
  • Neighbour switches forward hello frames out of their non root designated ports, identifying root, with their cost added.
  • If a switch does not receive BPDU frame, continues as normal until Max Age. STP Convergence
    There are four port states concern with STP topology convergence:
  • Blocking
  • Listening
  • Learning
  • Forwarding
Switch waits Max Age time, place in the listening state for Forward Delay time, place in the learning state for Forward Delay time and then place in the forwarding state. Switch must also timeout entries in MAC address table.
  • Max Age: 20 seconds (blocking to listening)
  • Forward Delay: 15 seconds (listening to learning)
  • Forward Delay: 15 seconds (learning to forwarding)   
     Optional Convergence Features of STP 
EtherChannel: provides a way to prevent STP convergence from being needed when only a single port/cable failure occurs. It combines from 2-8 parallel Ethernet trunks between same pair of switch, which STP treats as a single link. It also provides more bandwidth. Both links to the same switch must fail for a switch to need STP convergence.
  • PortFast: Allows a switch to place a port in the forwarding state immediately when the port becomes physically active (only safely done when device is not a bridge/switch)
  • Cisco BPDU Guard Feature: If enabled, tells the switch to disable PortFast ports if BPDU is received on those ports. Rapid Spanning Tree Protocol
The Intel pro set IEEE Rapid Spanning Tree Protocol (RSTP) can be used alongside 802.1d STP for switches that support RSTP. The assignment of forwarding and blocking ports are same in both STP and RSTP, the main reason to use RSTP is to overcome the convergence time and therefore it supposes the spanning tree best practice.

RSTP Convergence
The RSTP convergence time is typically less than 10 seconds as compare to the traditional convergence time of 50 seconds. In case of link between switch and a hub that is called Link-Type shared, RSTP does not improve convergence.

Optional Convergence Features of RSTP
  • Edge-Type Point-to-Point: It is link between the switches and just like PortFast in STP, RSTP immediately places Edge-Type into forwarding state.
  • Link-Type Point-to-Point: It is link between switch/end user. RSTP recognizes lost hello frames must three times faster than the STP default of 6 seconds. It also removes the requirement for listening state and through proposal and agreement messages reduces the time for learning state.

Wednesday, January 15, 2014

Cisco Switch Commands

Cisco Switches

Cisco IOS software is installed in the manageable Cisco switches for better management of the LAN. The Cisco's IOS software delivers network services and enabled networked applications. The Cisco IOS has a command line interface helps you to execute the Cisco IOS commands.

Cisco Switch Commands

The Cisco switch IOS have different EXEC modes with distinctive prompts. You can use these modes for executing different Cisco switch commands. Each mode has a set of specific commands.
The fundamentals of Cisco IOS User Interface are as follows :
  • Uses a command line interface
  • Operations vary on different series of switches
  • Type or paste entries in the console command modes
  • Enter key instructs device to parse and execute the commands
  • Two primary EXEC modes are user mode and privileged mode
  • Command modes have distinctive prompts

Cisco IOS Software Exec

There are two main EXEC modes for entering the Cisco switch commands:

User Mode

·  Limited examination of switch
·  Command prompt on the switch is switch

Privileged Mode

·  Detailed examination of switch
·  Enables configuration and debugging
·  Prerequisites for other configuration modes
·  Command prompt on the router is switches#

Cisco Telnet Commands

There are two primary methods for accessing a Cisco manageable switch to use command line interface.
·  Out of band Console connection
·  Via Ethernet through Telnet
Telnet is a utility used for remotely login to a device. To telnet a Cisco IOS switch from your computer, you have to type the following command on the CMD terminal of your computer:
Telnet ip address of the switch Just like:

Cisco Catalyst 1900 Switch Commands

Followings are some basic commands of Cisco Catalyst 1900 switch commands:
·  Show running-config: This command displays the memory status of the Cisco Catalyst 1900 switch
·  Show interfaces: This command displays the detailed information about all the interfaces of Cisco Catalyst 1900 switch.
·  Show interfaces Ethernet 0/1: This command displays the detailed information about a specific 10baseT Ethernet interface of the Cisco Catalyst 1900 switch
·  Show interfaces Fast Ethernet 0/26: This command displays the detailed information about a specific 100baseT Fast Ethernet interface of the Cisco Catalyst 1900 switch
·  Show ip: This command displays the ip configuration of the Cisco Catalyst 1900 switch
·  Show Mac-address-table: This command displays the Mac addresses of the devices that are currently connected to the Cisco Catalyst 1900 switch.
·  Show Mac-address-table security: This command displays the address table size and the addressing security of each interface of the Cisco Catalyst 1900 switch.
·  Show VLAN: This command displays the status of current VLANs enabled on the Cisco Catalyst 1900 switch.
·  Show VLAN-membership: This command displays the VLAN membership of all the ports on the Cisco Catalyst 1900 switch.
·  Show Spantree 1: This command displays the complete information about the spanning tree protocol 1 that is by default enabled on the Cisco Catalyst 1900 switch.
·  Copy nvram tftp: //host/dst_file: This command is used to send the configuration to a TFTP server.
·  Copy tftp: //host/src_file nvram: This command is used to download the configuration from a TFTP server.
·  Delete nvram: This command is used to reset the system configuration to factory defaults.

Show Cisco Switch Commands

Here are some show commands of Cisco switches:
·  Show version: This command displays the hardware and software status of the Cisco switch
·  Show flash: This command displays the files and directories in the flash of the Cisco switch
·  Show interfaces: This command displays the detailed information about all the interfaces of the Cisco switch
·  Show interfaces fast Ethernet 0/x: This command displays the detailed information about the specific interface of the Cisco switch
·  Show interfaces VLAN 1: This command displays the ip address configuration of VLAN 1
·  Show running-config:This command displays the status of RAM
·  Show startup-config:This command displays the status of NVRAM
·  Show-mac-address-table: This command displays the MAC address of the devices that are directly connected with any port of the switch.
·  Show port-security: [interface] [address]: This command displays the port security options on the interface
·  Show history: This command displays the last ten commands that are executed in the switch configuration
·  Show line: This command is used to view the brief information about all the lines of the Cisco switch
·  Show line console 0: This command is used to view the detailed information about the specific line of the Cisco switch
·  Erase startup-config: This command is used to erase the nvram of the Cisco switch

Cisco Switch Configuration Commands

·  Configure terminal: This command is used to enter in the global configuration mode of the Cisco switch
·  Hostname: This command is used to assign the hostname of the Cisco switch
·  Enable password: This command is used to set the enable password of the Cisco switch
·  Enable secret: This command is used to set the encrypted password of the Cisco switch that is used for entering in the privileged mode
·  Interface VLAN 1: This is a global configuration command used to configure the VLAN interface of the Cisco switch
·  Interface fast Ethernet 0/x: This command is used to configure the specific interface of the Cisco switch
·  IP address: This command is used to configure the ip address of any interface of the Cisco switch
·  IP default-gateway: This is an interface configuration command to set the default gateway
·  Speed: This command is used to set the speed for the interface of the Cisco switch
·  Duplex: This command is used to set the duplex setting for the interface of the Cisco switch
·  Line console 0: This command is used to enter in the specific line configuration mode of the Cisco switch
·  Password: This command is used to set the password of any line of the Cisco switch

Cisco IOS

As you know that Cisco is the worldwide leader in providing the hardware solutions as well as the software solutions of LAN and WAN. The hardware solutions mean that the hardware devices such as switches and routers etc but what is the meaning of software solution? The software solution actually means that Cisco manufactures manageable devices with a CLI based Cisco IOS Software installed in these devices. With the help of this software you can better manage your network and internetwork environment.

Once you have performed and inspection on the physical components of the Cisco switches and the routers, locate and record the IOS version being used by the router or switch with the show version command. In the display of show version command, the second line lists the following IOS running on a router or switch like:

4500 Software (C 4500-JS-M), version 11.2 (11)
The IOS was developed for a 4500 model router.
The major release 11.2 with the maintenance release (11)
The IOS runs from RAM (-M)

This is reconfirmed in the middle of the show version display with the following line:

System image file is "flash: c4500-js-mz_112-11.bin", booted via flash

This line list the file name as it appears in the flash memory of router.

Knowing how to determine what release and what type of IOS is running on a switch or router is important and critical for proper router administration and configuration. Different IOS images possess different capabilities and features for example, if the IOS is pre-11.2 release, you can not configure integrated routing and bridging or NAT on that router or there is no support of named access lists on that router. Selecting the correct set of IOS feature and the exact version is essential to maintain optimal router and switch performance.
Cisco IOS Download

To download Cisco IOS for a given router or switch, three key elements to be aware of are as follows:
The platform of router and switch
Software Feature Set

If you have the proper Cisco maintenance agreement then you have the privileges to download multiple IOS images directly from the official website of Cisco. Cisco has an"IOS planner" that guides you through the selection process of Cisco IOS under Software Centre on the Cisco website.

If you use the Cisco IOS planner, the first parameter to be selected is the platform of router or switch. Once a platform has been selected, then a major release must be selected. The recent router IOS releases are:
Cisco IOS release 10.3
Cisco OS release 11.0
Cisco IOS release 11.1
Cisco IOS release 11.2
Cisco IOS release 11.3
Cisco IOS release 12.0
Cisco IOS release 12.1
Cisco IOS release 12.2
Cisco IOS release 12.3

If you want the latest IOS releases then select Cisco IOS 12.4 download from the Cisco website.
Cisco IOS Commands

Here are the some basic Cisco IOS commands including in the Cisco IOS command line reference book and are used for configuring and verifying the configuration of the Cisco routers and switches:
ip address [address][subnet mask]: This command is used to configure ip address on an interface of the Cisco routers and switches.
bandwidth: This command is used for setting the bandwidth of the specific interface of the Cisco routers and switches.
shutdown: This command is used to shutdown a specific interface of the Cisco routers and switches.
interface fast Ethernet 0/x: This command is used for entering in the interface configuration mode of the Cisco routers and switches.
hostname [name]: This command is used to assign the hostname to Cisco routers and switches.
line vty 0 5: This command is used for entering in the line VTY configuration mode of the Cisco routers and switches.
line con 0: This command is used for entering in the line console configuration mode of the Cisco routers and switches.
line aux 0: This command is used for entering in the line auxiliary configuration mode of the Cisco routers and switches.
login: This command tells the Cisco routers and switches to ask for password.
password [password]: This command is used to set the line password in the Cisco routers and switches.
enable password [password]: This command is used to set the password for entering the privileged mode of the Cisco routers and switches.
enable secret [password]: This command is used to set the encrypted password for entering the privileged mode of the Cisco routers and switches.
configure terminal: This command is used to enter the global configuration mode of the Cisco routers and switches.
show interfaces serial 0: This command displays the detailed information about a specific interface.
show interfaces: This command displays detailed information about all the interfaces of Cisco routers and switches.
show line: This command displays the status of all the lines in the Cisco routers and switches.
show running-config: This command displays the current configurations of the Cisco routers and switches.
show startup-config: This command displays the saved configurations of the Cisco routers and switches.
show version: This command displays the hardware and software status of the Cisco routers and switches.
show flash: This command displays the files and directories reside in the flash of the Cisco routers and switches.
show history: This command displays the last ten commands that you were performed in the Cisco routers and switches.
erase startup-config: This command erases the nvram of the Cisco routers and switches.

Wednesday, January 23, 2013

Ques 32:- What is the difference between Industry standard Routing Protocol and Cisco Standard Routing Protocol?

Except Cisco All of the Company Router Are Only Support Industry Standard Routing protocol. This Company Router Only Support RIP & OSPF Routing protocol in The Network.

But Cisco Have developed Own routing protocol that is Called Cisco Standard Routing protocol. IGRP & EIGRP Is the Cisco standard Routing protocol in the network. Cisco Are Talking About – My Routing protocol Is More intelligent routing protocol than RIP & OSPF. And he is also talking about If U Will Use my router, My Router Supports All of the routing protocol in the network. Such As—RIP, IGRP, EIGRP, OSPF

Wednesday, December 8, 2010

Networking Answers:

Networking Answers:

How do I obtain the IP address of my computer?
(A): For Windows 95/98/ME, select 'run' from the start menu
and type WINIPCFG.
(B): For Windows NT/2000/XP, select RUN from the start menu and type CMD. This will bring up command prompt. Type: "ipconfig /all"


How do I release/renew my IP address?

From a command prompt type:" ipconfig /release": or "ipconfig /renew"


If I have a 4 Port Router but need to connect 5 computers to the Internet. What do I need to do?

You will need to add a switch to your network. After you setup the router accordingly, connect one port from the router to a switch using an Ethernet cable and then connect the rest of your stations to the switch. So if you have 5 stations, 3 of them will be connected to the router and the rest will be connected on the switch.


What is the difference between a Hub, Switch, and Router?

Hubs operate at ISO layer 1 - physical layer, Switches operate at ISO layer 2 - data link layer, and Routers operate at ISO layer 3 - network layer.
HUB: When Ethernet was originally designed it used a single fat coax called a backbone. Individual hosts were physically connected to the backbone. This created a party line. Each host had to listen for the backbone to be idle before it started talking. It was possible for more then one host to start talking at the same time. In that case, the messages collided making them unintelligible. When this condition was detected each transmitter stopped talking and waited a variable time interval before attempting to talk again.
The Ethernet network was named a "collision domain" since all devices waited until the line was clear or they would interfere with one another.
When Ethernet was modified to run over Unshielded Twisted
Pair (UTP) Category rated wiring, the original coax backbone
was shrunk within the hub, called a "collapsed backbone".
Functionally, a hub operates exactly as the old coax backbone. The ports on the hub provide a point-to-point connection to the Ethernet interface in each computer. With a hub, each node must wait for the network to be idle and detect collisions between multiple nodes.

SWITCH: As Ethernet networks grew in speed and size, the party line nature was recognized as a performance limitation.
Switches eliminate the collision domain and work much like a telephone switching system. When an Ethernet packet arrives at the switch, the destination MAC address is examined and the packet is switched to the proper port.
Each Ethernet interface has a 48-bit Media Access Controller (MAC) address assigned by the hardware vendor. The switch remembers which MAC addresses are connected to each port.
If the switch does not know which port to use it floods the packet to all ports. When it gets a response it updates its internal MAC address table. This means Port A can talk to C at the same time F is talking to B. This greatly increases overall performance even though it does not change the speed of individual connections. By eliminating the collision domain, connections are able to use full duplex. Hosts are able to transmit and receive at the same time, improving performance even more.

ROUTER: A router is used to interconnect multiple networks.
The Internet is literally "INTER-NETwork" -- a network of networks. Internet routers use IP addresses to determine how best to interconnect the sender to the destination. Because routers work at the IP layer, different physical networks can be interconnected; Ethernet, Token Ring, Sonet, even RS232 serial used for dialup can carry IP packets. Routers intended for home use include Network Address Translation (NAT). This allows a single address assigned by the ISP to be shared by multiple hosts connected to the local network.


What is UPnP?

Universal Plug and Play (UPnP) is an architecture for pervasive peer-to-peer network connectivity of PCs and intelligent devices or appliances, particularly within the home. UPnP builds on Internet standards and technologies, such as TCP/IP, HTTP, and XML, to enable these devices to automatically connect with one another and work together to make networking possible for more people.


What is NAT? Why is it used?

Network Address Translation (NAT) is an Internet Engineering
Task Force (IETF) standard used to allow multiple PCs or devices on a private network (networks using private address ranges such as 10.0.x.x, 192.168.x.x, 172.x.x.x) to share a single, globally routable IPv4 address. NAT is often deployed because IPv4, the current generation of the Internet addresses, are getting scarce.

NAT is used in gateway devices that form the boundary between the public Internet and the private LAN. As IP packets from the private LAN traverse the gateway, NAT translates a private IP address and port number to a public IP address and port number, tracking those translations to keep individual sessions intact.

Internet Connection Sharing in Microsoft Windows XP and
Windows Me operating systems, along with many Internet gateway devices, use NAT, particularly to connect to broadband networks via DSL or cable modems. The use of NAT is increasing dramatically as more homes and small businesses network their PCs and share a connection to the Internet.


What is the difference between TCP and UDP?

TCP is a protocol based on a connection between two computers. It is used for normal Internet traffic and applications such as web servers, FTP, etc. UDP is a protocol based on connectionless communication. UDP is ideal for applications like video streaming and online gaming, where lost packets don't need to be retransmitted and speed takes precedence.


What are the requirements for Full Duplex?

For a network to support Full Duplex, both devices must support and be configured for Full Duplex. Full Duplex is intended to increase the speed of a direct link between two devices; i.e., between switches or between a workstation and a switch. Switches support Full Duplex; hubs do not. Configuring an adapter for Full Duplex operation while connected to a hub could cause issues such as slowness or device drop-offs.


What is a converter?

A converter is a device that repeats and/or converts the signal from different media within the same transmission speed, e.g., 100Base-TX to 100Base-FX or 10Base-2 to 10Base-T.


Can a 100Base-TX/100Base-FX Converter be used with a Fast Ethernet Hub or Fast Ethernet Switch?
It can be used with either. However, the distances vary for both. You can have up to 2,000 meters of Multi-mode fiber optic cable with Fast Ethernet under Full Duplex mode, but only up to 200 meters with a Fast Ethernet Hub under half-duplex mode.


What is Auto MDI/MDIX?

Auto-MDIX (or Auto-crossover) is another negotiation that can occur between two Ethernet entities. This allows these entities to decide which wire pair to use for transmitting frames and which wire pair to use for receiving frames.
This feature is attractive when connecting two switches as this would normally require the use of a special cross-over cable. With Auto-MDIX, the two switches negotiate which wire pairs to use when communicating and this allows the use of standard (straight-through) cables when connecting two switches or two end devices.


What is the difference between Managed and Unmanaged Switches?

A managed switch is generally more expensive than an unmanaged switch, however, with this additional cost, extra features are provided. A managed switch is basically a switch that supports SNMP (Simple Network Management Protocol).
Of course, most managed switches provide features beyond SNMP. Basically, a managed switch allows you to take control of your network. An unmanaged switch will simply allow Ethernet devices to communicate. You connect your Ethernet devices to the unmanaged switch and they usually communicate automatically. There will be status LEDs to give you some feedback regarding link and activity; but this is generally all you get. With a managed switch you will have the same status LEDs, but the managed switch will let you adjust your communication parameters to any setting you desire and let you monitor the network behavior in a number of different ways.
For example, in systems that communicate in high noise environments, it is sometimes advantageous to force the data rate to 10 Mbps because noise coupled into the cables may confuse the auto-negotiation process. Most managed switches will allow you to set the data rate of each port. These environments can also benefit from disabling Auto-MDIX support since this negotiation can become confused by noise. Again, a managed switch is normally required to enable or disable these features on a port-by-port basis.
With a managed switch you can also monitor the network. Through SNMP, you can view a multitude of network statistics.
This includes the number of bytes transmitted and received, the number of frames transmitted and received, the number of errors, or the port status. All of this can be viewed on an individual port basis. Some managed switches even make this data available via a web server so that you can use a standard browser to view the network status. Managed switches offer advanced features that enhance your control of the network.

What is IGMP?

Internet Group Management Protocol (IGMP) is a protocol that governs the management of multicast groups in a TCP/IP network. This feature expedites streaming audio and video into a multiple user environment such as a classroom or lecture hall.
With IGMP, each multi-media request is transmitted only to appropriate users. Unlike Broadcast, Multicast makes efficient use of the available bandwidth reducing network impact.
All hosts conforming to level 2 of the IP multicasting specification require IGMP.


What is SNMP?
Simple Network Management Protocol is a standard for gathering statistical data about network traffic and the behavior of network components. SNMP uses Management Information Bases (MIBs), which define what information is available from any manageable network device.


What is VLAN?

A VLAN is a group of PCs, servers and other network resources that behave as if they were connected to a single, network segment - even though they may not be. The resources and servers of other users in the collocation facility will be invisible to each of the other VLAN members. Equally important, VLANs help meet performance needs by segmenting the network more effectively. Unlike standard switching, they restrict the dissemination of broadcast as well as node-to-node traffic, so the burden of extraneous traffic is reduced throughout the network. Security can also be improved. Since all packets traveling between VLANs may also pass through a router, standard router-based security measures can be implemented to restrict access as needed.
16. What is a GBIC? A GBIC (GigaBit Interface Converter) is a transceiver that converts serial electronic signals to optical signals and vice versa. In networking, a GBIC is used to interface a fiber optic system with an Ethernet system, such as Fiber Channel and Gigabit Ethernet. A GBIC allows designers to create one type of device that can be adapted for either optical or copper applications. Also GBICs are hot-swappable, which adds to the ease of upgrading high performance electro-optical communication networks.


What is a GBIC?

A Fast Ethernet Switch is the best solution for Ethernet and Fast Ethernet connection due to it’s built-in Auto-Negotiation (10/100) feature.


Why Choose Gigabit Ethernet over Fast Ethernet?
Gigabit Ethernet (1000Mbps) is 10 times faster than Fast Ethernet networks (100Mbps) and provides faster throughput for video, multimedia, graphics, Internet surfing, and other speed-intensive applications. It also has stronger error detection and correction capability.


How can I connect an existing Fast Ethernet network with a Gigabit Ethernet network?

A Gigabit Ethernet Switch is the best solution for Gigabit Ethernet and Fast Ethernet connections due to its built-in Auto-Negotiation (10/100/1000) feature.


How many pairs are needed for Gigabit Ethernet?

Gigabit Ethernet uses all 4 pairs (8 conductors). The transmission scheme is radically different because each conductor is used for send and receive.


What is the distance limitation of Gigabit Ethernet compared to Fast Ethernet?
Cable Type
Cable Length
Category 5/6 UTP
Category 5/5e/6 UTP
Category 5e/6 UTP
Multi-mode Fiber (MMF) with 62.5 micron core; 850 nm laser
MMF with 50 micron core; 1300 nm laser
MMF with 62.5 micron core;1300 nm laser
Single Mode Fiber with 9 micron core; 1300 nm laser


What is a common cause of two computers not seeing each other in a network?

To connect two computers together directly without a hub, the UTP cable has to be a crossover. A common mistake is to use a pin-to-pin cable. Make sure a crossover cable is used.

Wireless Networking Answers:


What is the difference between 802.11a, 802.11b, and 802.11g?
Wireless Standard
Wireless Standard
Wireless Standard
5 GHz
2.4 GHz
2.4 GHz
Underused 5 GHz band can coexist
with 2.4 GHz networks without interference
Heavily used 2.4 GHz band. Interference from other
2.4 GHz devices such as cordless phones, microwave ovens, etc.
may occur
Heavily used 2.4 GHz band. Interference from other
2.4 GHz devices such as cordless phones, microwave ovens, etc.
may occur

54 Mbps
11 Mbps
54 Mbps
5X greater than 802.11b
Cable modem service typically averages no
more than 4 to 5 Mbps
5X greater than 802.11b
Average Actual
27 Mbps
4-5 Mbps
20-25 Mbps
# Channels /
12 / 8
11 / 3
11 / 3
(Range will depend on antenna gain, transmit power, the receive sensitivity of the radio card and any obstacles between path ends.)
Shorter range than 802.11b and 802.11g. Due to higher operating frequency, typically offers less range and is less capable of working through wall and floors.
Better range than 802.11a. 2.4 GHz signal travel farther, and can work through walls and floors more effectively than 5 GHz signals
Better range than 802.11a. 2.4 GHz signal
travel farther, and can work through walls
and floors more effectively than 5 GHz signals
Incompatible with
802.11b or 802.11g
Widely adopted. Will work
in 802.11g networks
Backwards compatible with 802.11b networks (at 11 Mbps);
Incompatible with 802.11a
User base still relatively small. Limited
selection on 802.11a equipment.
Currently has the largest user base. 802.11b is currently used in most hot spots including airports, hotels, campuses, and public areas. Wide selection of 802.11b equipment.
Latest ratified standard. With speeds up to 5 times faster than 802.11b, Expect this standard to overtake 802.11b as the standard of choice.
Most expensive
Since this standard's ratification, prices have dropped significantly. Pricing is competitive with 802.11b. Cheaper than 802.11a
Excellent speed, unaffected by 2.4 GHz devices, can co-exist with 802.11b and 802.11g networks without interference
Largest user base, cheapest, used in most public hot spots, largest user base, wide selection of equipment
The speed of 802.11a with the range of 802.11b, compatible with 802.11b networks and hotspots, affordable


Does the number of antennae matter?

Not much. The majority of wireless routers have two antennae, most Access Points have one. However this is mostly a design choice by the manufacturer.


What is the difference between an Access Point and a Wireless Router?

An Access Point is a radio transmitter/receiver that is most widely used to bridge wireless and wired Ethernet networks.

A Router has additional functions: It allows multiple clients to connect to the Internet by serving internal IP addresses, has NAT capabilities, and often contains a built-in switch as well. It has the functionality of a Router and an Access Point in a single unit.


What factors impact wireless signal performance?
A wireless network's performance is affected by a variety of factors, such as the distance between nodes, walls/obstacles that obstruct direct line-of-sight, and other wireless traffic in the general area (such as the presence of 802.11b devices in the 802.11g network, or the presence proprietary non-standard WiFi technologies). Cordless phones, Bluetooth devices, microwaves, and anything that may cause interference in the 2.4GHz frequency range can affect the WLAN performance as well.


How do I secure my wireless network?
You can greatly reduce the security risks associated with running a wireless network by following the general rules below:
1.     Change the SSID. Change it to something unique to this AP/router. Also turn off the router's broadcasting. SSID broadcasting advertises your WLAN to everyone within range.
2.     Enable WEP - it encrypts data packets on the WLAN.
Although there are some flaws in WEP that enable a dedicated attacker to eventually break in, it will fence your network from the casual hacker that doesn't have a day or two to hang around capturing traffic.
3.     MAC Address filtering - some Access Points have the ability to filter only trusted MAC addresses. Every network device has a supposedly unique MAC address and the idea is to authorize only selected network devices to connect to the WLAN. The disadvantages of this feature are that you have to manually add authorized MAC addresses for all clients and that an intruder can still sniff those authorized MAC addresses (sent in clear text over the network) and possibly fake their own MAC address. Use this feature only if necessary, considering the drawbacks above.
4.     Only provide coverage for the areas that need access - lowering the transmit level on commercial class equipment, using directional antennas where needed reduces the coverage area and range where an attacker can penetrate your network.


What is 64/128bit WEP security?

Wired Equivalent Privacy (WEP) is a wireless network security protocol that encrypts transmitted data. Without any security, your data can be intercepted without difficulty. WEP encryption has three settings: Off (no security), 64-bit (weak security), 128-bit (a bit better security).
* Note: 40-bit and 64-bit WEP encryptions are the same; 40-bit devices can communicate with 64-bit devices.

_ 40-or 64-bit ASCII WEP code has 5 characters
_ 40- or 64-bit HEX WEP code has 10 characters
_ 128-bit ASCII WEP code has 13 characters
_ 128-bit HEX WEP code has 26 characters


What is SSID?
SSID, or Service Set Identifier, is the workgroup name of your Wireless Network. All devices (Access Points, Wireless Routers, and Wireless Network Adapters) must have the same
SSID to communicate on the Wireless Network.
Changing your SSID is recommended. Since the SSID is publicly transmitted, do not use personal information. The SSID has nothing to do with security; it simply is a name for your wireless network.


My wireless connection drops. What should I do?

Try to keep the antenna at least 6 inches away from the wall or other objects. If you are using 2.4GHz cordless phones, X-10 equipment, home security systems, ceiling fans, or certain lights, your wireless connection may degrade dramatically or drop altogether.
To avoid interference, also try changing the channel on your router, access point or other network device. Keep your product at least 3-6 feet away from electrical devices that generate RF noise, such as microwaves, monitors, electric motors, etc.


What is Ad-Hoc mode?

It is a set of wireless stations that communicate directly with one another without using an access point or any connection to a wired network.


What is Infrastructure?
In an infrastructure mode network the wireless network interface card needs an access point: all data is transferred using the access point as the central hub. All wireless nodes in an infrastructure mode network connect to an access point. All nodes connecting to the access point must have the same SSID as the access point, and if the access point is enabled with WEP, they must have the same WEP key or other authentication parameters.

Power over Ethernet (PoE)


What is the difference between midspan and endspan PoE?
A midspan PoE device is Power Sourcing Equipment (PSE) that inserts power onto the Ethernet cable. It is situated between the LAN switch and the Power Device (PD). Typically, midspan devices are added to existing networks to allow the use of PoE-enabled PDs.

An endspan device is typically a switch that incorporates PoE capabilities. To avoid adding midspan devices as well as a switch, endspan devices are often implemented when a new network is created.


What is a PD?
PD stands for Powered Device. It is an Ethernet device that receives power over Ethernet. It could be a PoE-enabled IP phone, a wireless access point, a serial device server, or any other IP device that requires power.


What is a PSE?
PSE stands for Power Sourcing Equipment. It is the network PoE element that inserts power onto an Ethernet cable. It may be an endspan device, such as a PoE-enabled switch, or a midspan device located between the switch and the PD.


What is the difference between a PoE Hub and a PoE Switch?
A Midspan PoE Hub does not have Ethernet switching capability. It is designed to be paired with an existing Ethernet switch, adding voltage for IEEE 802.3af compliant devices as needed. Midspan Hubs feature from 4 to 24 ports.

PoE Switches, on the other hand, come in port increments from 12 to 48 ports and offer both 10/100/1000 Ethernet managed switching capabilities and PoE injection.


How can a regular remote device work with PoE Equipment?
You will need a PoE Splitter Adapter. A PoE Splitter provides Ethernet data and DC power to a network device that is not compliant with the standard (non-PoE). This adapter effectively provides Ethernet data and DC power to a non-PoE device with a single cable and allows it to operate within a PoE network.


What is the power output from a PoE device?

Standard 802.3af properties
§  Voltage between 44V and 57V (48V is most common)
§  Maximal current :550mA
§  Maximal trigger current: 500mA
§  Typical current: 10mA - 350mA
§  Overload detection: 350mA - 500mA
§  Maximal demand of 5mA in idle condition
According to the 802.3af standard, the maximal power that can be transmitted over the Ethernet is 15.4W. This value is sufficient for a majority of IP-phones that use between 3W and 5.5W. Web cameras and wireless access points of networks consume more, between 6W and 10W. The same holds true for the majority of embedded PCs and Ethernet devices with their power dissipation around 10W.


What are some of the benefits of a PoE Network?
11.  _ Saves money
12.  _ Fast and easy to install
13.  _ Reduces overall power consumption
14.  _ Minimizes installation costs
15.  _ Reduces cable runs
16.  _ IEEE 802.3af is a unified, worldwide standard

Structured Cabling Answers:


What are the major UTP cable Categories?

Category 3 - (16 MHz) is mainly used for 10Base-T applications.
Category 5e - (100Mhz) is used for 100Base-T, 100Base-TX, and 1000Base applications. As compared to Cat 5 cable, it has improved specifications for NEXT, PSELFEXT, and Attenuation.
Category 6 - (250 MHz) As compared to Cat 5e cable, it has improved specifications for NEXT, PSELFEXT, and Attenuation.
Category 7 - Category 7 is a proposed standard that would support transmission at frequencies up to 600 MHz over 100 ohm twisted pair.


What is the 568A or 568B wiring configuration?


When should I use 568A or 568B?

It doesn't matter. Both are approved by the TIA/EIA 568. Both have the same performance. What you need to avoid is terminating one end of the run in 568A and the other end in 568B. That would cross pairs 2 and 3. Make sure your wiring is consistent.


What is a crossover cable?
A crossover cable is a 2-pair cable that crosses over pins 1,2/3,6. This cable is normally used to connect 2 computers directly or cascade two hubs without the use of an uplink port.


What do STP and UTP mean?

STP (Shielded Twisted Pair) is a type of copper wiring where a pair of wires is twisted around each other and covered in an insulating tube. The covering is designed to protect the wire from electromagnetic interference and serves as a ground. This extra protection, however, limits the wire's flexibility. The extra protection also means that STP cable is more expensive than other cable types. STP cable is commonly used in Ethernet networks.
UTP ( Unshielded Twisted Pair) cabling is the most common cable used in computer networking. It is a variant of twisted pair cabling. UTP cables are often called "Ethernet cables" after Ethernet, the most common data networking standard that utilizes UTP cables.
In contrast to STP cabling, UTP cable is not surrounded by any shielding. Due to the high flexibility of the UTP cable, it is the primary wire type for telephone usage and is very common for computer networking, especially in patch cables or temporary network connections.


What does category 6 do for my current network versus category 5e?
Because of its improved transmission performance and superior immunity from external noise, systems operating over category 6 cabling will have fewer errors versus category 5e for current applications. This means fewer re-transmissions of lost or corrupted data packets under certain conditions, which translates into higher reliability for category 6 networks.


What effect does workmanship and equipment have upon cabling performance?
A primary reason channel and link tests have evolved is due to the quality of the workmanship and materials. Channel performance is greatly affected by cable characteristics, connecting hardware, patch cords, and cross-connect wiring, as well as the total number of connections and the care with which they are installed and maintained. You can go a long way toward preserving performance by simply choosing good quality components and installing them with care and proper techniques.


Why should I test the cable immediately after pull-in?

This simplifies subsequent troubleshooting. By testing the system at this point, should a problem arise after the equipment is installed, the cabling system can be ruled out as a probable cause.


What are the maximum lengths for Ethernet cable?
Gigabit Ethernet (over copper) 1000Base-T:
1000 meters
Fast Ethernet, 100Base-T, 100Base-TX:
100 meters
Twisted Pair Ethernet, 10Base-T:
100 meters
Thin Ethernet, 10Base-2 :
185 meters
Thick Ethernet, 10Base-5:
500 meters


Can I use telephone patch cords to connect a LAN?
Using telephone cords to connect a LAN is not recommended. Telephone cords are designed to work with low speed applications such as voice transmission.


Do I need a special tool when working with 110-Type patch panels and jacks?

Yes, you need to use a 110-Type impact tool to properly terminate your connections.


What is Crosstalk?

Crosstalk is the unwanted introduction of signals from one channel or pair to another.


What is difference between a "Channel" and a "Link"?
These terms describe two Category certification tests. These tests differ in how much of a horizontal cabling run is included in the testing. The basic difference is that a link includes only the permanent part of the cable run while a channel includes and/or equipment cords as well.

Fiber Optic answers:


What is Multi-mode and Single Mode fiber?
Multi-mode fiber cable has a large-diameter core and has multiple pathways of light. Several wavelengths of light are used in the fiber core. Its primary use is for voice and data applications. Common core sizes include 50µm and 62.5µm with 1300 nm - 850nm Wavelength range for short distance transmission.Single-mode fiber has a small core and only one pathway of light. Single-mode fiber realigns the light toward the center of the core instead of bouncing it off the edge of the core as with Multi-mode. Core size is 8.3µm with 1550 nm - 1300n Wavelength range for long distance transmission.


How far can I connect by using Multi-mode or Single Mode fiber optic cable?
Multi-mode fiber optic cable connects up to 2,000 meters when the network is operated in Full Duplex mode. It can connect up to only 200 meters in Half Duplex mode. Single mode fiber optic cable can transmit from 15,000 meters to 60,000 meters, depending on hardware and configuration.


What is 50-micron and 62.5-micron fiber optic cable?
Physically, the two fiber types differ in the diameter of their core, which is the light-carrying region of the fiber. The 62.5µ fiber's core has a diameter of 62.5-micron and 50µ cable has a diameter the 50-micron.
The biggest difference between 50-micron and 62.5-micron cable is in bandwidth: 50-micron cable features three times the bandwidth of standard 62.5-micron cable. Other differences are distance and speed. As the data rate goes up (MHz), the distance that rate can be transmitted (km), goes down. Thus, a higher fiber bandwidth enables you to transmit at higher data rates for longer distances:


Do media converters add a point of failure to the network?
Why would I want to use them? Media converters have extremely high reliability statistics. In fact, although some companies have viewed them as a temporary migration solution, they have been so pleased with their performance that they have made them permanent. Media converters are ideal for companies that want to upgrade parts of their network and need increased bandwidth or higher transmission speed rates now, while at the same time leveraging existing electronics.


Since fiber is made of glass, will it survive harsh conditions?
Optical fiber is not your typical kind of glass. Made of ultra-pure silica, it is an extremely strong material that has the ability to handle exposure to extreme temperature and pressure. In fact, tensile strength (resistance to pulling) of optical fiber exceeds 600,000 pounds per square inch -- making it stronger than copper.


What do the abbreviations "ST, SC (connector)" mean?

ST (Straight Tip) - Optical fiber connector identified by its bayonet housing. The housing may be metallic or plastic.
SC (Subscriber Connector) - Optical fiber connector identified by the square cross-section of its plastic housing.


What is an LC connector?

LC connector is one of the upcoming standards in the field of Small Form Factor (SFF) connectors. It features a ceramic ferrule and looks like a mini SC connector. The LC interface is widely supported by the members of the LC Alliance, offering transceivers, connectors, cable assemblies, and companion hardware such as patch panels and wall outlets. Over 2,000,000 LC connectors are in field use, making it the most widely used SFF connector in the world.


What are the Fiber Standards and Working Distances?
Cable Type
Data Rate (Mbps)
Multi-mode 62.5/125 or 50/125
Single Mode
Single Mode
Multi-mode 62.5/125
Multi-mode 50/125
Single Mode

Audio and Video


What is the difference between Composite, S-Video, and Component Video?
Composite - The video signal is carried through a single "pin". It is the format of an analog television (picture only) signal.
S-Video - It has better connection than a composite video but the actual bandwidth is the same as composite video. The real benefit of an S-video connection is that it can reduce dot crawl, hanging dots, and crawling edges that appear on the vertical and horizontal edges (respectively) of some colored objects in the picture. It is an analog video signal that carries the video data as two separate signals (brightness and color), unlike composite video which carries the entire set of signals in one package. S-Video works in 480i or 720p resolution.
Component Video - Component video is a type of analog video information that is transmitted or stored as two or more separate signals. It uses a three jack cluster of wires with the ends color coded "green, blue, and red". The component video was invented to simplify video electronics and reduce the overall bandwidth requirements for transmitting video. It provides one luminance signal with full horizontal resolution and two color signals with reduced horizontal resolution.
Component video takes advantage of the superior picture found in such signal sources as HDTV and progressive DVD. Component works in 480i, 480p, 720p, 1080I, and 1080p resolution.


What is the resolution for 480i, 720p, 1080i?
Digital TV - SDTV:
§  480i - 704x480 interlaced
§  480p - 704x480 progressive
Digital - HDTV:
§  720p - 1280x720 progressive
§  1080i - 1920x1080 interlaced
§  1080p - 1920x1080 progressive


What is the difference between Interlace and Progressive scanning?
Interlaced scanning - This is a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines. This presents an entire frame/picture in 1/30th of a second with a refresh rate of 30Hz and produces 30 frames per second.
Progressive scanning - This is a scanning method which all the horizontal lines are scanned on to the screen at one time. The Digital TV and HDTV Standards accept both Interlaced Scan and Progressive Scan broadcast and display methods. Progressive Scan has long been used in Computer Monitors. It has a refresh rate of 60Hz and produces 60 frames per second.


What is Digital Audio?
"Digital" means information is stored in a binary format (made up of ones and zeroes). Digital audio refers to audio signals stored/transferred in a digital format.


What is the real difference between Coaxial Digital and Digital Fiber Optical Connections?
Coaxial and Optical are basically the same over short runs.
Over long runs, optical is better at preserving the signal since it has a lower amount of signal degradation. An optical cable needs to have the audio signal converted to light pulses while the coaxial cable will pass along the digital signal without any conversion.