Routing : 

Routing is the process by which a packet gets from one direction to another. To route a packet , a router needs to know the destination and on what interface to send the traffic out. when a packet comes into an interface on a route , it looks up the destination IP address in the packet header and compares it with its routing table. The routing table , which is stored in RAM, tells the router which outgoing interface the packet should go to reach destination network.

 

There are three ways to control routing decision on router :

• Static routes


• Default routes 


• Dynamic routes

Static Route:  Use a static route when you want to manually define the path that packet will take through your network. Static routes are useful in small network with rarely changing routes, when you have  little bandwidth and do not want the overhead of a dynamic routing protocol or when you want to manually define all of your routes for security reasons .

Static routes are created in Global Configuration mode.

The syntax for the static route in follows :

Route # IP route Destination network address [subnet mask] next-hop-address| interface 

Default routes: This is the special type of static route , commonly called the gateway of last resort. If the specially destination is not listed in the routing table, the default route  can be used to route the packet. A default route has an IP Address of 0.0.0.0 and a subnet mask of 0.0.0.0 , often represented as 0.0.0.0/0 . Default routes are commonly used in small network on a perimeter router pointing to the directly connected ISP router.

Dynamic Routes: Dynamic routes are routes that a router learns by using a routing protocol. Routing protocols will learn about routes from other neighbouring routers running the same routing protocol. Dynamic routing protocols share network numbers a router knows about and how to reach these networks. Through this sharing process, a router can learn about all of the reachable network numbers in the network.

Routing protocol and routed protocol: A routing protocol learn about routes for a routed protocol.

Routed Protocol : Any Network protocol that provides enough information in its network layer address to enable a packet to be forwarded from one host to another host based on the addressing scheme , without knowing the entire path from source to destination. Packets generally are conveyed from end system to end system IP is an example of routed protocol.

Routing Protocol: Facilities the exchange of routing information between networks , enabling routers to build routing tables dynamically. Traditional IP routing stays simple because it uses next hop (next router) routing in which the router needs to consider only where it sends the packet and does not need to consider the subsequent path of the packets on the remaining hops  (routers) .

*** RIP (Routing information protocol) is an example of a routing protocol.

There are two types of routing protocol: 

• Interior gateways protocols (IGP) :  These routing protocols exchange routing information within autonomous system. Routing infomation protocol version 2 (RIP V2) , enhanced Interior gateway routing (EIGRP) and open shortest path first (OSPE) are examples of IGPs.


• Exterior Gateways Protocol (EGP) : These routing protocols are used to route between autonomous system. Border Gateways protocol (BGP) is the EGP of choice in network today.

A router

In packet-switched  networks such as the internet, a router is a device or, in some cases, software on a computer, that determines the best way for a packet  to be forwarded to its destination.

A router connects networks. based on its current understanding of the state of the network it is connected to, a router acts as a dispatcher as it decides which way to send each information packet. A router is located at any gateway (where one network meets another), including each point of pressence on the internet. A router is often included as part of a network switch.

How does a router work?

A router may create or maintain a table of the available routes and their conditions and use this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network points with routers before arriving at its destination. Routing is a function associated with the network layer (layer3) in the standard model of network programming, the Open Systems Interconnection (OSI) model. A layer 3 switch is a switch that can perform routing functions.

An edge router is a device located at the boundary of a network that connects to other networks, wide area networks or the internet. For home and business computer users who have high-speed internet connections such as cable, satellite or DSL, a router can act as a hardware firewall. Many engineers believe that the use of a router provides better protection against hacking than a software firewall because no computer internet protocol addresses are directly exposed to the internet. This makes port scans (a technique for exploring weaknesses) essentially impossible. In addition, a router does not consume computer resources, which a software firewall does. Commercially manufactured routers are easy to install and are available for hard-wired or wireless networks.

Useful links

https://www.youtube.com/watch?v=9LhkW_dkZvU

https://mynetworkinglearningabc.wordpress.com/2014/07/26/routing-brief-description-about-routing/

https://en.wikipedia.org/wiki/Router_(computing)

Fifth editiopn Computer networks by Tanenbaum and David J. Wetherall

Posted by Lubega Fred.