Why Routing is necessary?
Routing is necessary whenever you have a network that needs to communicate with other networks. Whether it’s within an organization, connecting to the internet, or establishing secure connections across different locations, you need routing.
Imagine a large corporation with multiple departments spread across different floors or buildings. There are situations where Routing is needed such as when employees from one department need to access resources in another department, or the organization is growing, and new departments are being added. Routing is required to communicate different departments. It allows for scalability, security, and efficient data transmission, ensuring that employees can collaborate and access the resources they need.
We have two types of routing, Static Route and Dynamic Route.
Static Route
A static route is a manually configured route in a network that is set up by a network administrator. We can configure static route by specifying the destination network and the next-hop router or exit interface
Advantages:
- Easy to configure and understand, suitable for small and stable networks.
- Provides precise control over routing decisions. Network administrators have full control over the routing table.
- Consumes less bandwidth and processing power compared to dynamic routing protocols.
Disadvantages:
- Requires manual updates if the network topology changes. Not suitable for highly dynamic environments.
- Becomes impractical in larger networks where the number of routes increases.
- As the network grows, managing a large number of static routes can become complex.
Static Route to Specific Remote Network
This refers to a particular network or subnet that is not directly connected to the router but can be reached through one of the router’s interfaces.
For instance, suppose you have a network with two subnets, A and B. If you want traffic from subnet A to reach subnet B, you would need to add a static route in the router of subnet A that explicitly states that traffic destined for subnet B should be forwarded to a specific gateway.
Static Route to Group of Range of Remote Networks
This means you want to specify a range of networks (a group) rather than just a single specific network. This is useful when you have multiple subnets that share a similar addressing scheme.
For example, let’s say you have multiple remote offices, each with their own subnets (e.g., 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24, etc.). Instead of creating individual static routes for each of these subnets, you can create a single static route that encompasses the entire range (e.g., 192.168.0.0/16) to direct traffic towards the appropriate gateway.
Static Route to Default Route
This is commonly used when you want to direct all unknown traffic to a specific gateway (usually the gateway that leads to the internet). It’s often denoted as 0.0.0.0/0 (which encompasses all possible IP addresses).
For example, in a network with multiple subnets, if you want any traffic not destined for those subnets to be sent out to the internet, you’d set up a static route with a destination of 0.0.0.0/0 (the default route) pointing to your internet gateway.
Dynamic Route
A dynamic route is a route that is automatically learned and updated by a routing protocol without manual intervention.
Advantages:
- Adapts to changes in the network topology automatically. Reduces the manual effort required for configuration.
- Well-suited for larger networks where the topology is dynamic.
- Dynamic routing protocols often provide built-in mechanisms for fault tolerance.
Disadvantages:
- Configuration and management can be more complex.
- Dynamic routing protocols may be susceptible to security vulnerabilities. Proper security measures need to be implemented.
Routing Protocol Categories
Interior Gateway Protocol (IGP)
Interior Gateway Protocol (IGP) is a type of routing protocol used to exchange routing information within a single Autonomous System (AS). An Autonomous System is a group of routers and IP networks managed by one organzation.
Interior Gateway Protocol (IGP) is used for routing within an organization’s internal network, data center, or a smaller network that operates under a unified administrative control. IGP can use either Distance Vector or Link State algorithms for routing within an autonomous system (AS).
Distance Vector
Distance Vector protocols determine the best path to a destination based on the number of hops (or “distance”) required to reach it. Each router maintains a table that lists the number of hops required to reach various networks. Distance Vector use Bellman-Ford or Diffusino Update Algorithm.
Periodically, routers exchange their routing tables with neighboring routers, which allows them to learn about available routes and their associated hop counts. They share their routing tables, which consist of network addresses and the number of hops needed to reach them.
Example Protocols:
- Routing Information Protocol (RIP)
- Routing Information Protocol version 2 (RIPv2)
- Interior Gateway Routing Protocol (IGRP), old, no longer use.
- Enhanced Interior Gateway Routing Protocol (EIGRP), new.
Link State
Link State routing protocols focus on building a complete topology of the network. Each router maintains a database (Link State Database) that contains information about all the routers and links in the network. Routers exchange information about the state of their links with all other routers in the network. This information is used to construct a full view of the network’s topology.
Example Protocols:
- Open Shortest Path First (OSPF)
- Intermediate System to Intermediate System (IS-IS)
Exterior Gateway Protocol (EGP)
Exterior Gateway Protocol (EGP) is a type of routing protocol used to exchange routing information between different autonomous systems on the internet. EGP is used for routing between different organizations, ISPs, or entities that are part of separate autonomous systems.
EGP has been largely replaced by Border Gateway Protocol (BGP), which is a type of Path Vector.
Path Vector
Path Vector routing is a type of routing algorithm used to determine the optimal path for data transmission between a source and a destination. In a Path Vector algorithm, each router maintains a routing table that includes not only information about the next-hop router but also a path vector.
Border Gateway Protocol (BGP) uses a path vector algorithm to make routing decisions, the router exchanges network reachability information with their nearest neighbors. It maintains a table of routes to reach different networks, along with a list of Autonomous Systems that the route has traversed. This path information helps BGP avoid loops and make informed routing decisions.
Metric
Metric helps routers determine the optimal path to a destination. Also, metrics are used by routing protocols to evaluate and compare routes. Different protocols use different metrics, such as hop count, bandwidth, delay, or a combination of factors. Below are some examples.
Routing Information Protocol (RIP)
- Metric: hop count.
Interior Gateway Routing Protocol (IGRP)
- Metric: IGRP uses a composite metric that includes bandwidth, delay, reliability, load, and MTU.
Open Shortest Path First (OSPF)
- Metric: OSPF uses a cost-based metric, which can be configured based on factors like bandwidth.
Intermediate System to Intermediate System (IS-IS)
- Metric: The metric used in IS-IS is a configurable value based on link bandwidth.
Administrative Distance
Administrative Distance is a measure of the reliability or trustworthiness of a routing source.
The lower an Administrative distance (AD) value, the more trusted a route is. The AD values for major routing protocols are:
- Directly connected: 0
- Statically configured: 1
- External BGP: 20
- EIGRP: 90
- IGRP: 100
- OSPF: 110
- IS-IS: 115
- RIP: 120
- External EIGRP: 170
- Internal BGP: 200
- Unreachable: 255
Administrative distance is useful when comparing routes from different routing protocols or prioritizing route sources to ensure stability and reliability in the overall route selection process. For example, if both RIP and EIGRP advertise a route to a destination, the router compares their administrative distances to decide which routing information to trust.
Conclusion
To sum up, we have learned about Static and Dynamic routing as well as theirs pros and cons. We have defined and classified Routing Protocol Categories such as IGP and EGP. The specific protocols within these categories, such as RIP, OSPF, and EIGRP, contribute unique strengths to network dynamics. In addition, factors like Administrative Distance and Metric further enhances the decision-making process for optimal routing.