Overview of Routing Techniques

Overview
Routing is a process of selecting the path along which the data can be
transferred from source to the destination. Routing is performed by a
special device known as a router.
Routing metrics and costs are used for determining the best route to the
destination. The factors used by the protocols to determine the shortest
path, these factors are known as a metric.

Metrics
The most common metrics are:
● Hop Count
● Delay
● Bandwidth
● Load
● Reliability

Default Routing
Default Routing is a technique in which a router is conﬁgured to send all the
packets to the same hop device, and it doesn't matter whether it belongs to a
particular network or not. A Packet is transmitted to the device for which it is
conﬁgured in default routing.

Static Routing
Static routing is a form of routing that occurs when a router uses a
manually configured routing entry, rather than information from a
dynamic routing traffic. Static routing can be used in stub networks,
or to provide a gateway of last report.

Features
● Minimal Load on CPU
● Full Administrative Control
● Easier to Configure
● Not Suitable for Larger Networks
● Time Consuming to Manage
● Problems on Link Failure

Uses:
● Static routing can be used for small networks that require only one or
two routes
● Static routing is often used to help transfer routing information from
one routing protocol to another( routing redistribution ).
● Complement to Dynamic Routing.

Dynamic/Adaptive Routing
Dynamic routing, also called adaptive routing, is a process where a router can
forward data via a different route or given destination based on the current
conditions of the communication circuits within a system
Dynamic routing protocols can be classified in several ways.:
● Interior and exterior gateway routing protocols
● Distance vector, path vector and link state routing protocols
● Classful and classless

Link State
Two phases
● Reliable Flooding
● Path calculation

Flooding
Link State Messages Used:
● Hello
● Database description
● Link-state request
● Link-state update
● Link-state acknowledgement

Distance Vector
A distance-vector routing (DVR) protocol in data networks determines the best route for
data packets based on distance. A DVR protocol requires that a router inform its
neighbors of topology changes periodically.
Bellman Ford – Each router maintains a Distance Vector table containing the distance
between itself and ALL possible destination nodes. Distances,based on a chosen metric,
are computed using information from the neighbors’ distance vectors.
Dx(y) = min { C(x,v) + Dv(y), Dx(y) } for each node y ∈ N

Algorithm
1. A router transmits its distance vector to each of its neighbors in a routing packet.
2. Each router receives and saves the most recently received distance vector from each of
its neighbors.
3. A router recalculates its distance vector when it receives a distance vector from a
neighbor containing different information than before.

Characteristics
● Periodic Updates
● Asynchronous
● Distributed
● Iterative

Path Vector
Path Vector Routing is a routing algorithm in unicast routing protocol of
network layer, and it is useful for interdomain routing.
The principle of path vector routing is similar to that of distance vector
routing. It assumes that there is one node in each autonomous system that
acts on behalf of the entire autonomous system, and is called Speaker node.

Functions
● Prevention Of Loop
● Policy Routing
● Optimum Path

Initial routing tables in path vector routing

Overview of Routing Techniques

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