CCNA Training Blog

What is routing loops

Routing loop is a network problem in which the packet continues to be routed in a circle without reaching to its destination network. A routing loop is a condition in which a packet is continuously transmitted within a series of routers without reaching to its destination. A routing loop can occur when two or more routers have incorrect routing information to destination network. Each time a packet forwarded back around the loop, it multiplies number of packet crossing that link. When any error occurs in the operation of routing algorithm and the path to the destination [...] Continue Reading…

Every network devices contain two types of software for their operation. First one is operating system and second is configuration file. Similar to the computer the operating system facilitates the basic operation of the networking devices. Configuration files contain the Cisco IOS command used to customize the different function of a Cisco device. All commands are executed by the IOS software when the device is booted or when commands are entered in the configuration mode.

The administrator creates the different configuration that defines the desire particular function of the device. A Cisco device contain two configuration files:

1. Startup Configuration File

This [...] Continue Reading…

This is the most common devices for interconnecting the local area network. The Switch provides the bridging functionality with greater efficiency and act as a multipoint bridge to connect devices in a local area network. Switch looks each data unit it received and determines from a physical address that is the MAC address, for which device the packet is intended and Switch out the packet towards that device. The Switch normally has a buffer for each link to which it is connected. When Switch receives a frame, it stores the packet in the buffer of the receiving link and [...] Continue Reading…

VLSM (Variable Length Subnet Mask) is simply a subnetting a subnet. After the network address is subnetted, those subnet can be further subnetted.VLSM is a sub-subnetting.

In routing protocols RIP v1 or IGRP not use VLSM means there is no field defines for subnet information in these protocols. This is called classfull routing. RIP and IGRP both are considered as classful routing protocol.

Classless routing protocol support the VLSM means these protocols define the field for the subnet information. Therefore we can use the VLSM with the classless routing protocols like RIPv2,EIGRP or OSPF.With the VLSM we can have different subnet [...] Continue Reading…

Routing protocol uses the metric to determine which route is best route for the destination. Some time router has more than one path for the destination network. To select the best path, the routing protocol must be able to evaluate and differentiate among available path. A metric is used to for this purpose. The metric determine which path is most preferable when there are multiple paths available for the same network. Different routing protocol uses different metrics such as RIP uses hop count, EIGRP uses bandwidth etc.

Metric parameter

Because each routing protocol uses the different metrics, two different routing protocols [...] Continue Reading…

Gateway potentially operates in all seven layers of the OSI model. A Gateway is a protocol converter and its main work to convert protocols among communication networks. A router transfer, accept and relays packets only across network using similar protocol on the other hand Gateway can accept a packet formatted for one protocol and convert it to the packet formatted for another protocol before forwarding it .

In the enterprise a Gateway is a host that routes the traffic from a workstation to the outside of the network. We have the network connection at our home and the ISP work [...] Continue Reading…

CIDR (Classless Interdomain Routing) that allows internet service provider to reduce the wasting of ip address by assigning a subnet to a company instead of the entire network. It also reduce the size of internet routing tables in the router.CIDR allows routing protocols to summarize multiple networks in a single route.With CIDR ip address and their subnet mask are written as four octet ,separated by period and follwed by a forward slash that represent the number of subnet mask.Example -172.16.1.0/24 is a Class B subnetted address and 24 shows the number of network bit in this address and the [...] Continue Reading…

OSPF is an open protocol.

It is based upon SPF algorithm written by Dijkstra.

OSPF is a link state routing protocol because it sends the information of link and their states to the directly connected neighbors.

OSPF support bandwidth VLSM,multicasting and CIDR.

OSPF is a classless routing protocol.

Administrative distance of OSPF is 110 and the metric is cost.

By default OSPF will load balance on equal path and maximum can be 16 paths.

Multicast address of OSPF is 224.0.0.5 and 224.0.0.6.

224.0.0.5 is the address of all OSPF router 224.0.0.6 is only for the DR’s(DR and BDR).

OSPF router creates three tables-

Neighbor table

Topology table

Routing table

Neighbor table contain [...] Continue Reading…

There are several advantages of link state routing protocols.

Its build a topological map

Link-state routing  protocols creates a topological map of the network topology.Distacne vector protocol do not have the topological map.Router that uses the distance vector protocol only contain the list of the network, which include the cost that indicate the distance and next-hop router that indicate the direction to those network.Link state protocol exchange link states,the SPF algorithm build a SPF tree of the entire network and using this tree each router determine the shortest path to the destination network.

Link state protocols provides fast convergence

Link state protocols provide [...] Continue Reading…

When there is no route defines the routing table for the destination network then only default static router are used. First connect two routers with a serial cable. Here one side of cable on router1 is acts as a DCE and the other side of cable on router 2 acts as a DTE.For making DCE we have to give clock rate and bandwidth.

Configuring the default route in two router and two PC are shown in the example:

Add two routers and two PC with the following configuration:

Router 1-
IP address on the serial port S0 is -20.0.0.1
Subnet mask-255.0.0.0
IP address on the [...] Continue Reading…