Routing Concept

ROUTING

Routing is the process in which packets get transferred between the different networks (source to destination). As its name ROUTER is a routing device.           

A ROUTER should know destination IP address and the interface to route a packet.

ROUTING WAYS:  There are 4 ways to control routing decisions and enable the router to select the next hop. They are as follow,

1.     Connected network

2.     Static routes

3.     Default routes

4.     Dynamic routes

1.Connected Network

In this routing the packet is directly transferred from one network to another, no need to configure routing on the router you only need to configure the interfaces by assigning the IP addresses and no shutdown command.

 

2.Static Routing

It is a manual routing . Administrator must configure all possible routes to each and every router to ensure full connectivity.

 

 BASIC CONFIGURATION:

#enable

#configure terminal

#hostname “----------”

#interface  “-----------”

#ip address   192.168.11.1   255.255.255.0

                        (IP Address)       (subnet mask)

#no shutdown

#exit

Static routing Syntax:

#IP route [destination network address][Subnet Mask] [next hope address |Interface].

Network address:

If IP is 192.168.11.2 then network address will 192.168.11.0.

 

3.DEFAULT ROUTING

It is also like static routing, but when we don’t know the destination network address then default routing is used. Same commands from static route are used here but instead of destination address we have to use 0.0.0.0 and for subnet mask 0.0.0.0 . 

Basic Configuration:

Here Basic configuration will same every time.

Default Route Syntax:

#IP route  0.0.0.0   0.0.0.0   [next hop address/exit interface].

 

4. Dynamic Routing

                 The routing table in dynamic routing changes on the basis of networks. So only the networks added to the router and router choose the best path based on routing protocol.

                 In dynamic routing there is no need to know destination networks, It is very reliable way to use.

Types of protocol in Dynamic Routing 

1. Distance vector [RIP, RIPv2, IGRP]
2. Link state Protocol [OSPF, IS-IS]
3. Hybrid/Advanced Routing [EIGRP]

1.Distance vector :  This protocol works with Bellman Algorithm. It uses classfull routing protocol and it is also called by "Routing By Rumor". Classfull routing protocol used in it. It contains RIP and IGRP routing.

RIP[Routing Information Protocol]

This is a dynamic protocol which has hop count metric. It is used to find the best path from source to destination over the network. Maximum hop counts is 15 and maximum routers are 16, Administrative distance is 120 for this protocol.

Basic Configuration : Same every time

 Syntax: 

#sh IP route [It will suggest the network IPs]

#configuration terminal

#router rip

#network "---------"[suggested network IPs ]

2.Link State Protocol : This protocol based on shortest path first[SPF] algorithm to find the best path. That algorithm is Dijkstra algorithm. There is a Link-state advertisements which is a small packet of routing information. The example is OSPF routing.

OSPF[Open Shortest Path First]

OSPF is a classless protocol. It provide a hierarchical design with VLSM and route summarization. This protocol is a successor of RIP, it works with Link-State Advertisement.

 Syntax: 

#configuration terminal 

#router OSPF <process id>

#network <network address> <wildcard mask> area 0

#end 

  note: Process id can be any number but not 0, 

           Wildcard mask is inverted of Subnet Mask [If subnet mask is 255.255.255.0     then wildcard mask will be 0.0.0.255]

            Area should be 0 for small networks.

3. Hybrid/Advanced Routing: A hybrid Routing protocol is the combine form of Distance vector and Link-State protocol. Hybrid routing based on Distance vector but having features of the Link State protocol.

EIGRP (Enhanced Interior Gateway Routing Protocol) is an example of Hybrid protocol.

EIGRP

 EIGRP has faster convergence. It does not send the LSA packet but sends distance vector updates which contain information about the network. It also has Link-State characteristics. It synchronizes routing tables between neighbors about the network.It provide the classless routing.

 
 Syntax: 

#Configuration terminal

#router eigrp 20  [you can take any ASN number here I used 20.   0 will reserved

                             ASN largest value is 65,535]

#network [suggested n/w IP]

#end