Routing Information Process
In the process of Routing information is moved between source and destination across internetworks and at least one intermediate node is encountered.
Layer at which Routing is carried out
This process is carried at Network Layer.
Routing and Bridging
If the same process is carried put at Link Layer it is called Bridging. Obviously information carried in the process of Routing and Bridging from source to destination is different.
Basic tasks involve in Routing
Basic activities involved in routing are:
Determining such route or path which is optimal
Data or information transportation in form of packets through internetwork
Optimal path selection
Routing Protocol decides the best path for the packets to travel. These routing protocols create and maintain routing tables which keep track of routing information. This routing information differs from protocol to protocol depending upon which protocol is being used.
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Routing table contains all kind of information. Router extracts information of next hop and destination hop from the routing table. Router can find the optimal path by sending packets to next hop and so on until reached the destination. Incase the packet is received router checks for the destination address. If the address does not matches to itself it tries to associate the address with the next hop.
Routers can communicate to each other in order to maintain the routes in the routing table through a sequence of messages. Route updating message consists of all parts of a route table. Router can analyze updates of all other routers and can sketch a detailed topology for the network. When a message is sent from one router to another it also informs other routers in the form of link information. This link information is very useful to sketch complete idea of topology in the network.
In most of the protocols switching methods and algorithms are the same. Host identifies when it must send packet to some other host. It
first inquires the routers address and sends packet to MAC address of the router with network address of the host at destination. With the packets destination protocol address, router identifies whether it can send the packet to next hop or not.
If router do not know how to send the packet:
Incase router does not know hot to forward the packet most probably it will drop the packet.
If router knows how to send the packet:
If it knows how to send then router changes the physical address to next hop and sends the packet. It is possible that next hop may be the final destination as well. If next hop is not the final destination then most probably it would be a router. The same process is will repeat at the other router and goes on until reaches the final destination. During this process physical address is changing but the protocol address is same all the time.
There are several routing algorithms. Every algorithm is based on some key goals which affect the operations of routing protocols. Each of these algorithms have unique impact on the network and its resources. There are some important characteristics on behalf of which we can categorize routing algorithms.
Goals of routing algorithms
Routing algorithms often have one or more of the following design goals:
Optimal route means the algorithm will select the best route which depends on weightings of the metric. Calculation of weights in metrics may include number of hops or delays.
Most algorithms are designed simple enough to achieve maximum efficiency.
With increasing efficiency overheads and bottlenecks may increase as well. So algorithms are designed to have minimum possible overheads.
Designers emphasized on stability of algorithms. Algorithms should have similar behavior under all circumstances.
Routing algorithms work correctly even at unforeseen or unusual circumstances. Proper testing under different risk environments is very necessary for these kind of algorithms.
Routing algorithm should definitely converge faster. Algorithms with slow convergence may create loop routes and outages.
Routing Algorithms are built keeping in mind the increasing requirements. They should be able to deal with the changing environment and they should be adaptable to a variety of conditions.
Types of Algorithms
Static and Dynamic Routing
Static algorithms are just table based mappings which are usually established by the network. These kind of algorithms are usually for such environments which are easily predictable or networks that are easy to design. Systems with static routing can not react when things change in the network.
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Dynamic routing can fiddle with changing network conditions by analyzing received routing update messages. If the message identifies that a network has been modified, the routing algorithm recalculates routes and updates messages. These messages infuse the network, interesting routers to revise their algorithms and modify their routing tables accordingly.
Singlepath and Multipath
A number of routing protocols maintain several paths to the same destination. These multipath algorithms allow traffic multiplexing over several lines. The advantages of multipath algorithms are clear that they can offer considerably better throughput and reliability. Process is known as load sharing.
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