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OSPF stands for Open Shortest Path First. Definition: OSPF is a routing protocol used to determine the best route for delivering the packets within an IP networks. It was published by the IETF to serve as an Interior Gateway Protocol replacing RIP. The OSPF specification is published as Request For Comments (RFC) 1247. Note that OSPF is a link-state routing protocol, whereas RIP and IGRP are distance-vector routing protocols. Routers running the distance-vector algorithm send all or a portion of their routing tables in routing-update messages to their neighbors. OSPF sends link-state advertisements (LSAs) to all other routers within the same area. Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. OSPF routers  use the SPF (Shortest Path First) algorithm to calculate the shortest path to each node. SPF algorithm is also known as Dijkstra algorithm. Advantages of OSPF OSPF is an open standard, not related to any partic

Cisco has defined a hierarchical model known as the hierarchical internetworking model. This model simplifies the task of building a reliable, scalable, and less expensive hierarchical internetwork because rather than focusing on packet construction, it focuses on the three functional areas, or layers, of your network: Core layer : This layer is considered the backbone of the network and includes the high-end switches and high-speed cables such as fiber cables. This layer of the network does not route traffic at the LAN. In addition, no packet manipulation is done by devices in this layer. Rather, this layer is concerned with speed and ensures reliable delivery of packets. Distribution layer : This layer includes LAN-based routers and layer 3 switches. This layer ensures that packets are properly routed between subnets and VLANs in your enterprise. This layer is also called the Workgroup layer. Access layer : This layer includes hubs and switches. This layer is also calle

RIP stands for Routing Information Protocol. RIP is a dynamic, distance vector routing protocol and was developed for smaller IP based networks. As mentioned earlier, RIP calculates the best route based on hop count. There are currently two versions of RIP protocol. RIPv1, and RIPv2 RIPv1: RIP version 1 is among the oldest protocols. Limitations of RIPv1: 1. Hop Count Limit: Destination that is more than 15 hops away is considered unreachable by RIPv1. 2. Classful Routing Only: RIP is a classful routing protocol. RIPv1 doesn't support classless routing. RIP v1 advertises all networks it knows as classful networks, so it is not possible to subnet a network using RIP v1. 3. Metric limitation: The best route in RIP is determined by counting the number of hops required to reach the destination. A lower hop count route is always preferred over a higher hop count route. One disadvantage of using hop count as metric is that if there is a route with one additional h

When IP packets travel over the Internet, routing information is exchanged between the devices that control the flow of information over the Internet. These devices are known as routers, and they use the IP address as the basis for controlling the traffic. These devices need to talk the same language to function properly, though they belong to different administrative domains. For example, one router may be in Newyork(US), and the receiving router may be in London (UK). It is necessary that a routing protocol is followed for smooth flow of traffic. Given below are the widely used routing protocols for routing Internet traffic: RIP v1 RIP v2 OSPF IGRP EIGRP BGP Notations used: Routing Information Protocol (RIP), Open Shortest Path First (OSPF), Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (EIGRP), and Border Gateway Protocol (BGP). One often get confused between a routing protocol and a routed protocol. A

What we discussed in the previous section is Classful subnet masking. A Subnetmask normally contains the host portion of the bits also. This is called Classless Inter Domain Routing (CIDR). This will enable more networks for a given class of network address. For example, allowing 3 host bits towards subnet portion in our previous IP address, will allow us to offer 2X2X2 or 8 additional subnetworks. Traditionally, all zeros, and all ones subnets are not used, and hence we are left with 6 subnets. 192.189.210.078: 1100 0000.1011 1101.1101 0010.0100 1110 Class C IP Address 255.255.255.224: 1111 1111.1111 1111.1111 1111.1110 0000 Class C subnet mask with 3 additional bits of host portion used for Subnetting. Broadcast address: 1100 0000.1011 1101.1101 0010.0101 1111 :192.189.210.95 The above is the broadcast address for a given subnet (192.189.210.078). Under Classful routing, the broadcast address would have been 192.189.210.255.

Subnetting an IP Network is done primarily for better utilization of available IP address space, and routing purpose. Other reasons include better organization, use of different physical media (such as Ethernet, WAN, etc.),  and securing network resources. A subnet mask enables you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. A logical AND operation between the IP address and the subnet mask provides the Network Address. For example, using our test IP address and the default Class C subnet mask, we get: 192.189.210.078: 1100 0000.1011 1101.1101 0010.0100 1110 Class C IP Address 255.255.255.000: 1111 1111.1111 1111.1111 1111.0000 0000 Default Class C subnet mask  192.189.210.0         1100 0000 1011 1101 1101 0010 0000 0000 As can be seen above, by using and AND operator, we can compute the network portion of an IP address.  The network portion for the

An IP address is a unique logical identifier for a node or host connection on an IP network. An IP address is a 32 bit binary number, and represented as 4 decimal values of 8 bits each. The decimal values range from 0 to 255. This is known as "dotted decimal" notation. Example: 192.189.210.078 It is sometimes useful to view the values in their binary form. 192     .189     .210     .078 11000000.10111101.11010010.1001110 Every IP address consists of network identifier and node identifier. The IP network is divided based on Class of network. The class of network is determined by the leading bits of the IP address as shown below. Address Classes There are 5 different address classes. You can determine which class any IP address is in by examining the first 4 bits of the IP address. Class A addresses begin with 0xxx , or 1 to 126 decimal. Class B addresses begin with 10xx , or 128 to 191 decim