What is Routing? Why it is important?
Routing is the main hub around which the entire IP connectivity of network revolves. We can also say that routing is the main element which establishes basic internetwork communication between network as well as implements an addressing structure which uniquely identifies every device which are connected with the network as well as organises virtual devices into a hierarchical network structure. There are hundreds of network routing protocols which are available in order to support communication between different electronic devices. Basically, routing protocols is the family of network protocols which enables one router to communicate with another router in order to intelligently forward the network traffic between different network. The routing protocols are divided into two categories which are discussed below:
- Interior Routing Protocol
The main purpose of Interior gateway protocol (IGP) is to handle routing within an Autonomous system. Autonomous system routing between router is handled by Interior gateway protocols. These dynamic routing protocols keep track of all the paths which can be used to transfer one data from one system to another system. These protocols fall under two different categories that are mentioned below:
- Distance vector protocol such as (RIP, IGRP, EIGRP)
Distance vector routing means that the router routes will be advertised by providing two characteristics that are distance and vector. Distance will identify how far is the target network based on the metric such as cost, delay, bandwidth and hop count etc. and on the other hand Vector will specify the direction of next hop router or we can say the interface needed for reaching a destination network. Now, we will discuss distance vector routing protocols.
- Routing Information Protocol (RIP)
RIP routing protocols are developed in the 1980s for small and medium-sized networks. This protocol is capable for routing message across networks up to 15 hops. This protocol defines how routers are going to forward their details across the interconnected group of local area network. RIP is a dynamic routing protocol which uses hop counts for routing metric in order to find the best path between destination and source network. This protocol works in the application layer of the OSI model and has port number 520. Moreover, there are 3 different versions of RIP protocol that are available RIP V1, RIP V2 and RIPng.
Some features of RIP Protocol are discussed below:
- During updates, full routing tables are sent.
- Routers exchange network updates periodically.
- RIP always broadcast the routing information.
- EIGRP and IGRP
IGRP stands for Internet Gateway Routing Protocol and is developed by Cisco. IGRP supports maximum hop count to 255 and moreover, this protocol sends new changes status every 90 seconds. This protocol is developed as another alternative for RIP protocol. However, EIGRP (Enhanced Interior Gateway protocol) protocol is developed which supports classless IP subnets and enhances the efficiency of EIGRP algorithm as compared to IGRP algorithm. EIGRP protocol does not support routing hierarchies like RIP. This is specially designed Cisco devices and is easier to configure and provide better performance as compared to OSPF routing protocol.
Some features of the IGRP protocol are discussed below:
- Routes updates are sent every 90 seconds.
- Hop count is limited to 1000 by default and is configurable to up to 255.
- It has an Administrative distance of 100.
Some features of EIGRP protocol are discussed below:
- This protocol supports VLSM subnets and supernets.
- This protocol provides fast convergence.
- This protocol consumes less bandwidth and there are no periodic updates, no broadcasts and updates only contain changes.
- This protocol supports multiple network layer protocols such as Appletalk, IP (Internet Protocol) and Novell Netware (IPX/SPX).
- Link State protocols such as (OSPF, IS-IS)
As compare to distance vector routing protocol operations the router which is configured with a link-state routing protocol will create an overall view of the network topology by gathering all the information from other routers. Now, we will discuss link state routing protocols.
- Open Shortest Path First (OSPF)
It is a routing protocol for Internet Protocol (IP) networks. OSPF uses LSR (Link State Routing) algorithm and falls in the group of IGPs (Interior Gateway protocols) which are operating in a single AS (Autonomous System). It works on port number 89. Basically, this protocol is created for overcoming some of the limitations of RIP protocol such as significant spikes of network traffic by repeatedly re-sending full router table a given time of intervals, the restriction of only 15 hop count etc. OSPF protocol enables the network by sending identification messages to each other which is further followed by messages that capture specific routing functions rather than the entire routing table.
Some features of OSPF protocol are discussed below:
- This protocol enables load balancing of network traffic between multiple paths of same metric value.
- This protocol supports authentication using passwords.
- OSPF enables logical grouping of network segments into a specific area.
- It supports VLSM (Variable Length Subnetting), CIDR, Super-netting and non-contiguous network segments.
- IS-IS (Intermediate System to Intermediate System)
It is a link-state routing protocol which is used in routers for exchanging topology information with their neighbours’ routers. The network information is flooded throughout the autonomous system (AS) so that each router of the network can have network topology updates. The main advantage of using link state routing protocol is that the router can find out shortest route for the data easily. This is helpful in traffic engineering purposes where routes can be constrained in order to find out best path in order to meet the best quality of service requirements.
Some features of the IS-IS protocol are discussed below:
- This routing protocol supports a hierarchical routing structure.
- IS-IS protocol supports CIDR, VLSM and discontinuous network.
- The convergence of IS-IS algorithm is very fast.
- This protocol uses IS-IS Hello (IIHs) PDUs in order to form adjacencies between routers.
2.Exterior Routing Protocol
This routing protocol is one of the important routing protocols which is used for exchanging data between neighbour’s gateway host which are present in Autonomous system. This protocol is based on periodic message exchange polling for neighbour reachability and poll commands for requesting update responses. Each router polls its neighbour at the interval between 120 to 480 seconds and after that neighbour responds by sending its complete routing table. The recent Exterior routing protocol is BGP (Border Gateway Protocol). BGP is the only routing protocol which is officially used over the Internet for connecting individual network with the Internet.
- BGP (Border Gateway Protocol)
BGP is a protocol that manages how packets should be routed between internet by exchanging routing and reachability information between edge routers. This protocol directly directs packets between AS (Autonomous system). The network traffic which is routed within a single AS network is called as Internal BGP (iBGP) and on the other hand BGP is used for connecting one AS with other AS which is non-external BGP (eBGP). This protocol selects the best route based on the routing policies rather than on technical characteristics of path.
Some features of BGP protocol are discussed below
- This protocol uses TCP for transferring of data and provide reliable delivery of BGP updates. 2.This protocol sends an update only when changes in the network get occur. 3.This protocol periodically sends a keepalive message in order to check the TCP connection.
So in the above sections, we have discussed some of the routing protocols which are used over the network in order to transfer data from one network to another network.: