Wednesday, November 28, 2012

Common Network Cable Types to Know

Cables are commonly used to carry communication signals within LAN. There are three common types of cable media that can be used to connect devices to a network and they are coaxial cable, twisted-pair cable, and fiber-optic cable.

Coaxial Cable
Coaxial cable looks similar to the cable used to carry TV signal. A solid-core copper wire runs down the middle of the cable. Around that solid-core copper wire is a layer of insulation, and covering that insulation is braided wire and metal foil, which shields against electromagnetic interference. A final layer of insulation covers the braided wire.

There are two types of coaxial cabling: thinnet and thicknet. Thinnet is a flexible coaxial cable about ¼ inches thick. Thinnet is used for short-distance. Thinnet connects directly to a workstation’s network adapter card using a British Naval Connector (BNC). The maximum length of thinnet is 185 meters. Thicknet coaxial is thicker cable than thinnet. Thicknet cable is about ½ inch thick and can support data transfer over longer distances than thinnet. Thicknet has a maximum cable length of 500 meters and usually is used as a backbone to connect several smaller thinnet-based networks.

The bandwidth for coaxial cable is 10 mbps (megabits per second).

Twisted Pair Cable
Twisted-pair cable is the most common type of cabling you can see in today’s LAN networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs. When a wire is carrying a current, the current creates a magnetic field around the wire. This field can interfere with signals on nearby wires. To eliminate this, pairs of wires carry signals in opposite directions, so that the two magnetic fields also occur in opposite directions and cancel each other out. This process is known as cancellation. Two Types of Twisted Pairs are Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP).

Unshielded twisted-pair (UTP) cable is the most common networking media. Unshielded twisted-pair (UTP) consists of four pairs of thin, copper wires covered in color-coded plastic insulation that are twisted together. The wire pairs are then covered with a plastic outer jacket. The connector used on a UTP cable is called a Registered Jack 45 (RJ-45) connector. UTP cables are of small diameter and it doesn’t need grounding.  Since there is no shielding for UTP cabling, it relies only on the cancellation to avoid noise. 

UTP cabling has different categories. Each category of UTP cabling was designed for a specific type of communication or transfer rate. The most popular categories in use today is 5, 5e and 6, which can reach transfer rates of over 1000 Mbps (1 Gbps).

The following table shows different UTP categories and corresponding transfer rate.
UTP Category
Transfer Rate
Category 1
Voice Only

Category 2
4 Mbps
Category 3
10 Mbps
Category 4
16 Mbps
Category 5
100 Mbps
Category 5e
1 Gbps
Category 6
1/10 Gbps

Optical Fiber Cabling
Optical Fiber cables use optical fibers that carry digital data signals in the form of modulated pulses of light. An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. There are two fibers per cable—one to transmit and one to receive. The core also can be an optical-quality clear plastic, and the cladding can be made up of gel that reflects signals back into the fiber to reduce signal loss.

There are two types of fiber optic cable: Single Mode Fibre (SMF) and Multi-Mode Fibre (MMF).
1. Single Mode Fibre (SMF) uses a single ray of light to carry transmission over long distances.
2. Multi Mode Fibre (MMF) uses multiple rays of light simultaneously with each ray of light running at a different reflection angle to carry the transmission over short distances

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Tuesday, November 20, 2012

Spanning Tree Protocol Standards /Types

Types of STP
Like many networking standards, there are many types or variants of STP. These include:
 PVST+, RSTP , Rapid-PVST+

These are public or industrial specification created by the IEEE. Some of these STP types are Cisco proprietary and others are IEEE standards.

You will learn more details on some of these STP variants, but to get started you need to have a general knowledge of what the key STP variants are. Below, is a brief description of the key Cisco and IEEE STP variants?

Cisco Proprietary
Per-VLAN Spanning Tree Protocol (PVST) - Maintains a spanning-tree instance for each VLAN configured in the network. It uses the Cisco proprietary ISL trunking protocol that allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs. Because PVST treats each VLAN as a separate network, it can load balance traffic at Layer 2 by forwarding some VLANs on one trunk and other VLANs on another trunk without causing a loop. For PVST, Cisco developed a number of proprietary extensions to the original IEEE 802.1D STP, such as BackboneFast, UplinkFast, and PortFast.

To learn more about these extensions, visit:

 Per-VLAN Spanning Tree Protocol Plus (PVST+) - Cisco developed PVST+ to provide support for IEEE 802.1Q trunking. PVST+ provides the same functionality as PVST, including the Cisco proprietary STP extensions. PVST+ is not supported on non-Cisco devices. PVST+ includes the PortFast enhancement called BPDU guard, and root guard.

To learn more about BPDU guard, visit:

To learn more about root guard, visit:

Rapid Per-VLAN Spanning Tree Protocol (rapid PVST+) - Based on the IEEE 802.1w standard and has a faster convergence than STP (standard 802.1D). Rapid PVST+ includes Cisco-proprietary extensions such as BackboneFast, UplinkFast, and PortFast.

IEEE Standards
Rapid Spanning Tree Protocol (RSTP) - First introduced in 1982 as an evolution of STP (802.1D standard). It provides faster spanning-tree convergence after a topology change. RSTP implements the Cisco-proprietary STP extensions, BackboneFast, UplinkFast, and PortFast, into the public standard. As of 2004, the IEEE has incorporated RSTP into 802.1D, identifying the specification as IEEE 802.1D-2004. So when you hear STP, think RSTP.

Multiple STP (MSTP) - Enables multiple VLANs to be mapped to the same spanning-tree instance, reducing the number of instances needed to support a large number of VLANs. MSTP was inspired by the Cisco-proprietary Multiple Instances STP (MISTP) and is an evolution of STP and RSTP. It was introduced in IEEE 802.1s as amendment to 802.1Q, 1998 edition. Standard IEEE 802.1Q-2003 now includes MSTP. MSTP provides for multiple forwarding paths for data traffic and enables load balancing.

To learn more about MSTP, visit:

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Wednesday, November 7, 2012

GUIDE to Redistribute Routing Protocols

Redistribution is when a routing protocol is used to advertise routes that are learned by some other means, such as static routes, directly connected routes, or by another routing protocol.

While it is desirable to run a single routing protocol throughout your entire IP internetwork, multi-protocol routing is common for a number of reasons, including company mergers, multiple departments managed by multiple network administrators, and multi-vendor environments.

Often, running different routing protocols is part of a network design.

A multiple protocol environment makes redistribution a necessity.

Differences in routing protocol characteristics (such as metrics, administrative distance classful, and classless capabilities) can affect redistribution.

For redistribution to be successful, these differences must be considered.
Note: When redistributing between a classful routing protocol (such as Routing Information Protocol Version 1 [RIP V1], Interior Gateway Routing Protocol [IGRP] ) and a classless routing protocol (such as Open Shortest Path First [OSPF]), RIP V2, Enhanced Interior Gateway Routing Protocol [EIGRP] ) will not advertise routes out an interface if those routes are on the same major network, but have a different mask than that particular interface.

For an example of how to redistribute RIP and OSPF refer to:

Note: When redistributing routes into OSPF, a common mistake is to omit the subnets keyword from the redistribution statement.

This prevents redistribution from taking place.

When there is mutual redistribution between routing protocols, there is the possibility of creating routing loops.

A routing loop is when one routing protocol announces a route learned by another routing protocol through redistribution.

To avoid this, never announce the information originally received from routing process x back into routing process x.

This can be done with the use of distribution lists or route maps.

For more information refer to the:

This section of the document explains how to use distribution lists or route maps to avoid redistribution problems.

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Monday, November 5, 2012

How to connect 2 WAN, 1 LAN through a Cisco router?

“Hi, I need a router, can connect 2 incoming Ethernet line (WAN), 1 output line (LAN), need 10/100/1000 ports. Would you recommend a router for me?” One customer from Chad asked.
Let’s share the solution for everyone.
1)    10/100/1000 ports Router:
1800 series router only have 10/100 Ethernet ports, can’t be chosen.
2800 series router, from CISCO2821 will have 2GE ports.
Description: 2821 w/ AC PWR, 2GE, 4HWICs, 3PVDM, 1NME-X, 2AIM, IPBASE, 128F/512D
So recommend CISCO2821 Router as the reasonable choice.
2)    Connect 2 incoming Ethernet line (WAN), 1 output line (LAN).
Need 3 GE ports, CISCO2821 include 2 GE port, then need add 1 GE ports at least.
a. HWIC-1GE-SFP+ GLC-T (MJ-45 normal cable connection)

b. HWIC-1GE-SFP + GLC-SX-MM/ GLC-LH-SM (optical fiber connection).

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