Describe four examples of routing metrics that can be used to determine the best path for a network

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Purpose of Routing Protocol Metrics:
RIP Metric Hop Count:
Administrative Distance:
Relationship between Administrative Distance and Routing Metric:
Types of Routing
Static Routing
Advantages Of Static Routing
Disadvantages of Static Routing:
Default Routing
Dynamic Routing
Advantages of Dynamic Routing:
Disadvantages of Dynamic Routing:

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Routing protocols are a set of rules which are used to define an optimal route between sources and destination systems in a network. Basically routing works on the network layer of the OSI reference model.

Purpose of Routing Protocol Metrics:

To determine the best route when multiple updates are received for the same route or we can say when various routes are learned so a router could receive routing updates from several other different routers all about the same network and it needs a mechanism to determine the best one well that’s where the metrics come into play and a metric is a numeric value and it’s different between each routing protocol it could be a small value or an immense value and routing protocol will look at the metric of all the similar route and it will use a lower metric to determine the best route so the general rule of thumb is the lower the metric the better the route and so a routing protocol will look and no compare and if it didn’t have a metric it would have all of these updates about the same network but it would not know which one to use it would have any basis to determine the best route so that’s the purpose to determine the best route.

Each Possible path will be assigned as a ‘metric’ value by the routing protocol which indicates how preferred the path is. Always the lowest metric value is preferred. Distance vector routers advertise to each other the networks they know about and their metrics to get to each of them.

Link state routers advertise all the links in their area of the network to each other.
Each router will take this information and then make independent calculations of its own best path to get to each destination.
If the best path to a destination is lost
For example: because a link went down it will be removed from the routing table and replaced with the next best route.

RIP Metric Hop Count:

RIP uses hop count as the metric.
The maximum hop count by default is 15. Paths that are more than 15 hops away are marked as unreadable.
RIP is typically used only in small or test environments.

S.NO	Routing Protocol	Metric
1.	RIP	Hop count
2.	EIGRP	bandwidth, delay
3.	OSPF	cost

Administrative Distance:

Administrative distance is a way to find reliable routing information, and a lower administrative distance means a route is more accurate. Administrative Distance is a default value assigned to each routing protocol that will favor the best route from one protocol over another one.

Example: Router receives multiple routes over to the 10.10.10.0/24 network from both the OSPF and RIP.

You can display the Administrative Distance in the router by typing the show IP route command in CLI:

Relationship between Administrative Distance and Routing Metric:

S.No.

Administrative distance

Routing Metric

Administrative Distance is used to choose the distance among multiple paths learned through different routing protocols

The metric is used to choose among multiple paths learned through the same protocol

It is considered to be the first to narrow the choice down to the single best routing protocol.

It is considered to choose the best path or paths which

make it into the routing table.

A Router is a process of selecting path along which the data can be transferred from source to the destination. Routing is performed by a special device known as a router.
A Router works at the network layer in the OSI model and internet layer in TCP/IP model
A router is a networking device that forwards the packet based on the information available in the packet header and forwarding table.
The routing algorithms are used for routing the packets. The routing algorithm is nothing but a software responsible for deciding the optimal path through which packet can be transmitted.
The routing protocols use the metric to determine the best path for the packet delivery. The metric is the standard of measurement such as hop count, bandwidth, delay, current load on the path, etc. used by the routing algorithm to determine the optimal path to the destination.
The routing algorithm initializes and maintains the routing table for the process of path determination.

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 are the network variables used to determine the best route to the destination. For some protocols use the static metrics means that their value cannot be changed and for some other routing protocols use the dynamic metrics means that their value can be assigned by the system administrator.

The most common metric values are given below:

Hop count: Hop count is defined as a metric that specifies the number of passes through internetworking devices such as a router, a packet must travel in a route to move from source to the destination. If the routing protocol considers the hop as a primary metric value, then the path with the least hop count will be considered as the best path to move from source to the destination.
Delay: It is a time taken by the router to process, queue and transmit a datagram to an interface. The protocols use this metric to determine the delay values for all the links along the path end-to-end. The path having the lowest delay value will be considered as the best path.
Bandwidth: The capacity of the link is known as a bandwidth of the link. The bandwidth is measured in terms of bits per second. The link that has a higher transfer rate like gigabit is preferred over the link that has the lower capacity like 56 kb. The protocol will determine the bandwidth capacity for all the links along the path, and the overall higher bandwidth will be considered as the best route.
Load: Load refers to the degree to which the network resource such as a router or network link is busy. A Load can be calculated in a variety of ways such as CPU utilization, packets processed per second. If the traffic increases, then the load value will also be increased. The load value changes with respect to the change in the traffic.
Reliability: Reliability is a metric factor may be composed of a fixed value. It depends on the network links, and its value is measured dynamically. Some networks go down more often than others. After network failure, some network links repaired more easily than other network links. Any reliability factor can be considered for the assignment of reliability ratings, which are generally numeric values assigned by the system administrator.

Types of Routing

Routing can be classified into three categories:

Static Routing
Default Routing
Dynamic Routing

Static Routing

Static Routing is also known as Nonadaptive Routing.
It is a technique in which the administrator manually adds the routes in a routing table.
A Router can send the packets for the destination along the route defined by the administrator.
In this technique, routing decisions are not made based on the condition or topology of the networks

Advantages Of Static Routing

Following are the advantages of Static Routing:

No Overhead: It has ho overhead on the CPU usage of the router. Therefore, the cheaper router can be used to obtain static routing.
Bandwidth: It has not bandwidth usage between the routers.
Security: It provides security as the system administrator is allowed only to have control over the routing to a particular network.

Disadvantages of Static Routing:

Following are the disadvantages of Static Routing:

For a large network, it becomes a very difficult task to add each route manually to the routing table.
The system administrator should have a good knowledge of a topology as he has to add each route manually.

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.
Default Routing is used when networks deal with the single exit point.
It is also useful when the bulk of transmission networks have to transmit the data to the same hp device.
When a specific route is mentioned in the routing table, the router will choose the specific route rather than the default route. The default route is chosen only when a specific route is not mentioned in the routing table.

Dynamic Routing

It is also known as Adaptive Routing.
It is a technique in which a router adds a new route in the routing table for each packet in response to the changes in the condition or topology of the network.
Dynamic protocols are used to discover the new routes to reach the destination.
In Dynamic Routing, RIP and OSPF are the protocols used to discover the new routes.
If any route goes down, then the automatic adjustment will be made to reach the destination.

The Dynamic protocol should have the following features:

All the routers must have the same dynamic routing protocol in order to exchange the routes.
If the router discovers any change in the condition or topology, then router broadcast this information to all other routers.