IP Routing

What is Routing?
IP routing is the process of moving packets from one network to another network and delivering the packets to hosts. In another way Routing is used for taking a packet from one device and sending it through the network to another device on different networks.

What is Routing Protocols and Routed Protocols?
A Routing protocol is used by router to dynamically find all the networks in the internetwork and to ensure that all routers have the same routing table. These routing protocols determine the path of a packet through an internetwork. Example of routing protocols is RIP, IGRP, EIGRP and OSPF. A Routed protocols can be used to send user data (packet) through the established enterprise. Routed protocols are assigned to an interface and determine the method of packet delivery. Example of routed protocols IP, Novell IPX, Telnet, SNMP, SMTP etc. Non-Routable protocols cannot be routed. A communication protocol that only a device address and not a network address. It doesn’t not incorporate an addressing scheme for sending data from one network to another. Eg; NetBIOS.

There are different types of routing
•    Static routing
•    Default routing
•    Dynamic routing

Static Routing
Static routing is the process of an administrator manually adding routes in each (individual router) router’s routing table. There are benefits and disadvantages to all routing processes.
-No overhead on the router CPU
-No bandwidth usage between routers
-Security (because the administrator only allows routing to certain networks)
-The administrator must know about all networks and how each router is connected to configure the routes correctly.
-If one network is added to the internetwork, the administrator must add a route to it on all routers.
-It’s not feasible in large networks because it would be a full-time job.

Router(config #ip route [destination network] [mask] [next hop address or exit interface] [administrative distance][permanent]

ip route The command used to create the static route.
Destination network The network you are placing in the routing table.
Mask Indicates the subnet mask being used on the network.
Next hop address The address of the next hop router that will receive the packet and forward it to the remote network router interface before you add the route.
Exit interface Used in place of the next hop address if desired.

Default Routing
Default routing is used to send packets with a remote destination network not in the routing table to the next hop router. You can only use default routing on stub networks, which means that they have only one exit port out of the network
Router(config)#ip classless
Router(config)#ip route s0/0 or

Send all packets destined for networks not in my routing table out my Serial 0/0 interface or Send all packets destined for networks not in my routing table to

All Cisco routers are classful routers, which mean they expect a default subnet mask on each interface of the router. When router receive a packet for a destination subnet not in the routing table, it will drop the packet by default. So we must use The IP Classless command because no remote subnets will be in the routing table.we should turn on the ip classless command when we set default routing.

Dynamic Routing
Dynamic routing is the process of using protocols to find and update routing tables on routers. This is very easier than static or default routing, its utilizing router CPU processes and bandwidth on the network links. A routing protocol defines the set of rules used by a router when it communicates between neighbor routers. The two types of routing protocols are Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP).
There are two types of routing protocols used in internetworks: Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP). IGP routing protocols are used to exchange routing information with routers in the same autonomous system (AS). An AS is a collection of networks under a common administrative domain. EGPs are used to communicate between AS’s. An example of an EGP is Border Gateway Protocol (BGP).
When configuring routing protocols we should be aware of administrative distances (ADs). These are used to rate the trustworthiness of routing information received on a router from a neighbor router. An administrative distance
is an integer from 0 to 255, where 0 is the most trusted and 255 means no traffic will be passed via this route.

Default Administrative Distances
Connected interface -0
Static route -1
IGRP -100
OSPF -110
RIP -120
External EIGRP -170
Unknown 255 (this route will never be used)

There are three classes of routing protocols:
Distance vector The distance-vector routing protocols use a distance toa remote network to find the best path. Each time a packet goes through a router, it’s called a hop. The route with the least number of hops to the network is determined to be the best route. The vector is the determination of direction to the remote network. Examples of distance-vector routing protocols are RIP and IGRP.

Link state Typically called shortest path first, the routers each create three separate tables. One of these tables keeps track of directly attached Neighbors, one determines the Topology of the entire internetwork, and one is used for the Routing table. Link-state routers know more about the internetwork than any distance-vector routing protocol. An example of an IP routing protocol that is completely link state is OSPF.
Hybrid Uses aspects of distance vector and link state, for example, EIGRP.