OSPF Tutorial

OSPF Tutorial

 

In this article we will learn about the OSPF Routing Protocol

Open-Shortest-Path-First (OSPF) is the most widely used interior gateway protocol routing protocol on the world because it is a public (non-proprietary) routing protocol while its biggest rival, EIGRP, is a Cisco proprietary protocol so other vendors can’t use it. OSPF is a complex link-state routing protocol. Link-state routing protocols generate routing updates only when a change occurs in the network topology. When a link changes state, the device that detected the change creates a link-state advertisement (LSA) concerning that link and sends to all neighboring devices using a special multicast address. Each routing device takes a copy of the LSA, updates its link-state database (LSDB), and forwards the LSA to all neighboring devices.

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EIGRP Tutorial

EIGRP Tutorial

In this article we will mention about the EIGRP protocol.

In the past, Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco-proprietary routing protocol but from March-2013 Cisco opens up EIGRP as an open standard in order to help companies operate in a multi-vendor environment. EIGRP is a classless routing protocol, meaning that it sends the subnet mask of its interfaces in routing updates, which use a complex metric based on bandwidth and delay.

EIGRP is referred to as a hybrid routing protocol because it has the characteristics of both distance-vector and link-state protocols but now Cisco refers it as an advanced distance vector protocol.

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IPv6 Tutorial

IPv6 Tutorial

Internet has been growing extremely fast so the IPv4 addresses are quickly approaching complete depletion. Although many organizations already use Network Address Translators (NATs) to map multiple private address spaces to a single public IP address but they have to face with other problems from NAT (the use of the same private address, security…). Moreover, many other devices than PC & laptop are requiring an IP address to go to the Internet. To solve these problems in long-term, a new version of the IP protocol – version 6 (IPv6) was created and developed.

IPv6 was created by the Internet Engineering Task Force (IETF), a standards body, as a replacement to IPv4 in 1998. So what happened with IPv5? IP Version 5 was defined for experimental reasons and never was deployed.

While IPv4 uses 32 bits to address the IP (provides approximately 2³² = 4,294,967,296 unique addresses – but in fact about 3.7 billion addresses are assignable because the IPv4 addressing system separates the addresses into classes and reserves addresses for multicasting, testing, and other specific uses), IPv6 uses up to 128 bits which provides 2¹²⁸ addresses or approximately 3.4 * 10³⁸ addresses. Well, maybe we should say it is extremely extremely extremely huge :)

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Access List Tutorial

Access List Tutorial

In this tutorial we will learn about access list.

Access control lists (ACLs) provide a means to filter packets by allowing a user to permit or deny IP packets from crossing specified interfaces. Just imagine you come to a fair and see the guardian checking tickets. He only allows people with suitable tickets to enter. Well, an access list’s function is same as that guardian.

Access lists filter network traffic by controlling whether packets are forwarded or blocked at the router’s interfaces based on the criteria you specified within the access list.

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Rapid Spanning Tree Protocol RSTP Tutorial

Rapid Spanning Tree Protocol RSTP Tutorial

Note: Before reading this article you should understand how STP works. So if you are not sure about STP, please read my article about Spanning Tree Protocol tutorial first.

Rapid Spanning Tree Protocol (RSTP)

One big disadvantage of STP is the low convergence which is very important in switched network. To overcome this problem, in 2001, the IEEE with document 802.1w introduced an evolution of the Spanning Tree Protocol: Rapid Spanning Tree Protocol (RSTP), which significantly reduces the convergence time after a topology change occurs in the network. While STP can take 30 to 50 seconds to transit from a blocking state to a forwarding state, RSTP is typically able to respond less than 10 seconds of a physical link failure.

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Spanning Tree Protocol STP Tutorial

Spanning Tree Protocol STP Tutorial – Premium Tutorial

To provide for fault tolerance, many networks implement redundant paths between devices using multiple switches. However, providing redundant paths between segments causes packets to be passed between the redundant paths endlessly. This condition is known as a bridging loop.

(Note: the terms bridge, switch are used interchangeably when discussing STP)

To prevent bridging loops, the IEEE 802.1d committee defined a standard called the spanning tree algorithm (STA), or spanning tree protocol (STP). Spanning-Tree Protocol is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between two stations.

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Cisco Command Line Interface CLI

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Cisco Command Line Interface CLI

In the previous tutorial we learned about the boot sequence of a Cisco router/switch. After that, the router will allow us to type commands but in different modes we can only used specific commands. So in this tutorial we will learn about the Command Line Interface (CLI) and different modes in a Cisco router/switch.

Below lists popular modes in Cisco switch/router:

Router>		User mode
Router#		Privileged mode
Router(config)#		Configuration mode
Router(config-if)#		Interface level (within configuration mode)
Router(config-router)#		Routing engine level (within configuration mode)
Router(config-line)#		Line level (vty, tty, async) within configuration mode

Now let’s discuss each mode in more detail

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Cisco Router Boot Sequence Tutorial

Cisco Router Boot Sequence Tutorial

 

In this article we will learn about the main components of a Cisco router and how the boot process takes place.

Types of memory

Generally Cisco routers (and switches) contain four types of memory:

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OSI Model Tutorial

OSI Model Tutorial

 

Welcome to the most basic tutorial for networker! Understanding about OSI model is one of the most important tools to help you grasp how networking devices like router, switch, PC… work.

Let’s take an example in our real life to demonstrate the OSI model. Maybe you have ever sent a mail to your friend, right? To do it, you have to follow these steps:

1. Write your letter
2. Insert it into an envelope
3. Write information about sender and receiver on that envelope
4. Stamp it
5. Go to the post office and drop it into a mail inbox

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EtherChannel Tutorial

EtherChannel Tutorial

EtherChannel is the technology which is used to combine several physical links between switches or routers into one logical connection and treat them as a single link. Let’s take an example to see the benefits of this technology:

Suppose your company has two switches connecting with each other via a FastEthernet link (100Mbps):

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Syslog Tutorial

Syslog Tutorial

As an administrator of a network, you have just completed all the configuration and they are working nicely. Now maybe the next thing you want to do is to set up something that can alert you when something goes wrong or down in your network. Syslog is an excellent tool for system monitoring and is almost always included in your distribution.

Places to store and display syslog messages

There are some places we can send syslog messages to:

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Simple Network Management Protocol SNMP Tutorial

Simple Network Management Protocol SNMP Tutorial

Building a working network is important but monitoring its health is as important as building it. Luckily we have tools to make administrator’s life easier and SNMP is one among of them. SNMP presents in most of the network regardless of the size of that network. And understanding how SNMP works is really important and that what we will learn in this tutorial.

Understand SNMP

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Gateway Load Balancing Protocol GLBP Tutorial

Gateway Load Balancing Protocol GLBP Tutorial

The main disadvantage of HSRP and VRRP is that only one gateway is elected to be the active gateway and used to forward traffic whilst the rest are unused until the active one fails. Gateway Load Balancing Protocol (GLBP) is a Cisco proprietary protocol and performs the similar function to HSRP and VRRP but it supports load balancing among members in a GLBP group. In this tutorial, we will learn how GLBP works.

Note: Although we can partially configure load balancing via HSRP or VRRP using multiple groups but we have to assign different default gateways on the hosts. If one group fails, we must reconfigure the default gateways on the hosts, which results in extra administrative burden.

GLBP Election

When the routers are configured to a GLBP group, they first elect one gateway to be the Active Virtual Gateway (AVG) for that group. The election is based on the priority of each gateway (highest priority wins). If all of them have the same priority then the gateway with the highest real IP address becomes the AVG. The AVG, in turn, assigns a virtual MAC address to each member of the GLBP group. Each gateway which is assigned a virtual MAC address is called Active Virtual Forwarder (AVF). A GLBP group only has a maximum of four AVFs. If there are more than 4 gateways in a GLBP group then the rest will become Standby Virtual Forwarder (SVF) which will take the place of a AVF in case of failure. The virtual MAC address in GLBP is 0007.b400.xxyy where xx is the GLBP group number and yy is the different number of each gateway (01, 02, 03…).

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Hot Standby Router Protocol HSRP Tutorial

Hot Standby Router Protocol HSRP Tutorial

In this tutorial we will learn what is HSRP and the need of HSRP in a network.

Most of the company in the world has a connection to the Internet. The picture below shows a most simple topology of such a company:



To make above topology work we need to:

+ Configure IP addresses on two interfaces of the Router. Suppose the IP address of Fa0/0 interface (the interface connecting to the switch) is 192.168.1.1.
+ Assign the IP addresses, default gateways and DNS servers on all PCs. In this case we have to set the default gateways to Fa0/0 interface (with the IP address 192.168.1.1) of the router. This can be done manually or automatically via DHCP.

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