ROUTING PROTOCOLS

ROUTING INFORMATION PROTOCOL (RIP)

R.I.P is one of the oldest DISTANCE VECTOR ROUTING PROTOCOLS. It uses hop count as a metric, with a maximum of 15 hops.

VERSIONS:

• RIPv1: Classful protocol, no subnet information.

• RIPv2: Classless, supports subnetting, includes subnet mask info. Multicast updates and simple authentication.

USE CASES:

• Suitable for small to medium-sized networks.

• Limited scalability, slower convergence compared to modern protocols like OSPF and EIGRP.

OPEN SHORTEST PATH FIRST (OSPF)

OSPF is a LINK-STATE-ROUTING PROTOCOL. It is a common Interior Gateway Routing Protocol that is used within a single Autonomous System (AS). It is available on routers from many different manufacturers

KEY FEATURES:

• Hierarchical design with areas to optimize traffic.

• Updates sent only when topology changes, reducing overhead.

• Supports VLSM (Variable Length Subnet Masking) and CIDR (Classless Inter-Domain Routing)

ADVANTAGES:

• Efficient, scalable, and flexible.

• Provides load balancing and fault tolerance

• Suitable for large, complex networks.

It is a Link-State Protocol, so routing is based on the connectivity between routers. Each link has cost based on throughput, reliability, round trip time and other factors.

The lowest cost and fastest path wins, while identical costs are load balanced.

ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL (EIGRP)

EIGRP is partly proprietary to Cisco, commonly used on internal Cisco-routed networks. It is a Hybrid Routing Protocol that is relatively easy to enable and use.

KEY FEATURES:

• Cleanly manage topology changes.

• Minimize bandwidth use by the efficient discovery of neighbor routers.

• Loop free operation.

• Supports VLSM and CIDR.

• Sends partial updates only when changes occur.

ADVANTAGES:

• Highly efficient, scalable and quick convergence.

• Provides loop-free paths and load balancing.

• Suitable for medium to large networks, especially those with Cisco devices.

AUTONOMOUS SYSTEM (AS)

An Autonomous system (AS) is a network or group of networks managed by a single administrative entity, often an internet service provider (ISP) or a large organization.

These systems are characterized by a unified routing policy that governs how data is routed within and between them. In essence, an AS is a building block of the internet, allowing for the efficient and coordinated transfer of data. 

• Single Administrative Domain:

  An AS operates under a common set of rules and policies, ensuring consistent routing behavior. 

• Routing:

  ASes use routing protocols to exchange information about reachable networks and determine the best paths for data packets to travel. 

• Internet Connectivity:

  The internet itself is composed of numerous autonomous systems that connect and exchange data.

BORDER GATEWAY PROTOCOL (BGP)

BGP is an Exterior Gateway Routing Protocol that is used around the world for WAN Internet connections by ISP’s.

KEY FEATURES:

• Supports CIDR for efficient IP address allocation

• Employs policies for route selection and advertisement

• Uses TCP for reliable communication between BGP peers.

ADVANTAGES:

• Highly scalable and flexible

• Manages large routing tables and complex policies.

• Crucial for ISP’s and large enterprises with multiple connections to the internet.

METRIC

The METRIC is a value associated with routes, used by routing protocols to evaluate the cost of path traversal.

Lower metric values typically indicate more desirable routes.

Different routing protocols may use various factors such as bandwidth, delay, hop count, or even custom values to calculate this metric.

DISTANCE VECTOR ROUTING

Distance Vector Routing is a protocol used by routers to determine the best path for data packets to travel across a network. It works by each router sharing information about its known network distances with its neighbors, and then updating its own routing table based on the received information. This process continues until all routers have a consistent view of the network topology and shortest paths. 

How it works:

• Distance Vectors:

  Each router maintains a table, called a distance vector, that lists the distances (usually measured in hops, or the number of routers a packet passes through) to all reachable destinations in the network. 

• Sharing Information:

  Routers periodically share their distance vectors with their directly connected neighbors. 

• Updating Tables:

  When a router receives a distance vector from a neighbor, it updates its own routing table by comparing the received distances with its current distances. If a shorter path to a destination is found through the neighbor, the router updates its table with the new, shorter path. 

• Convergence:

  This process of exchanging and updating distance vectors continues until all routers have the most accurate information about the network topology, and the system has "converged". 

Key Concepts:

• Hops:

  A common metric for measuring distance in distance vector routing, representing the number of routers a packet passes through to reach a destination. 

• Routing Table:

  A table maintained by each router that lists the best known paths (with corresponding distances) to all reachable destinations. 

• Neighbors:

  Routers that are directly connected to each other. 

• Convergence:

  The state where all routers have consistent and accurate information about the network topology. 

LINK STATE ROUTING PROTOCOL

A Link-State Routing Protocol is a routing protocol that enables routers to build a complete map of the network topology by exchanging information about the directly connected links.

Each router then uses this information, typically with Dijkstra's algorithm, to calculate the shortest paths to all other destinations in the network. Unlike distance-vector protocols, link-state protocols flood the network with link-state updates when changes occur, leading to faster convergence. 

Key Concepts:

• Link State:

  Each router advertises the state of its directly connected links, including the cost or metric associated with each link. 

• Flooding:

  When a router detects a change in its link state, it floods this information throughout the network, ensuring all routers have the same topology information. 

• Dijkstra's Algorithm:

  This algorithm is commonly used by each router to compute the shortest paths to all other routers based on the received link-state information. 

• Neighbor Discovery:

  Routers use HELLO messages to discover and establish relationships with their directly connected neighbors. 

• Link State Database (LSDB):

  Each router maintains a database containing information about the entire network topology, including link costs. 

How it works:

1. Neighbor Discovery: Routers exchange HELLO messages to identify their immediate neighbors. 

2. Link Cost Measurement: Routers determine the cost of each link (e.g., delay, bandwidth). 

3. Link State Advertisement (LSA): Each router creates an LSA containing its neighbors and link costs and floods this information throughout the network. 

4. Database Synchronization: Routers update their LSDBs with the received LSAs. 

5. Route Calculation: Each router uses Dijkstra's algorithm (or a similar algorithm) to compute the shortest paths based on its LSDB. 

Advantages of Link-State Routing: 

• Faster Convergence: Link-state protocols generally converge faster than distance-vector protocols when network topology changes occur. 

• More Accurate Topology Information: Each router has a complete picture of the network topology, allowing for more efficient route calculations. 

• Loop-Free Paths: Dijkstra's algorithm ensures loop-free paths are calculated. 

Disadvantages:

• Higher Memory Requirements:

  Maintaining a database of the entire network topology requires more memory.

• Higher CPU Usage:

  Calculating shortest paths using Dijkstra's algorithm can be computationally intensive, especially in large networks.

• Bandwidth Consumption During Flooding:

  Flooding LSAs can consume bandwidth, particularly during initial startup or when there are frequent network changes. 

Examples of Link-State Routing Protocols: 

• OSPF (Open Shortest Path First): A widely used protocol, especially in enterprise networks, according to Lenovo. 

• IS-IS (Intermediate System to Intermediate System): Often used in large service provider networks, says Lenovo. 

• NLSP (NetWare Link Services Protocol): A link-state protocol used in Novell networks, according to OpenText. 

• OLSR (Optimized Link State Routing Protocol): A link-state routing protocol designed for ad hoc networks. 

Intermediate System to Intermediate System (IS-IS)

IS-IS is a routing protocol used in computer networks to efficiently move data. It is a Link-State Protocol, meaning routers exchange information about network topology to build a map of the entire network, and then use that map to calculate the best routes for data transmission.

IS-IS is commonly used in large service provider networks and can also be deployed in large enterprise networks, according to Cisco.

Key Characteristics:

• Link-State Protocol:

  IS-IS routers maintain a database of the network topology, including information about connected devices and links. This allows them to make informed routing decisions. 

• Dijkstra's Algorithm:

  IS-IS uses Dijkstra's algorithm (also known as SPF - Shortest Path First) to calculate the shortest path to each destination in the network. 

• Interior Gateway Protocol (IGP):

  IS-IS is designed to operate within a single autonomous system (AS) or routing domain. 

• Hierarchy:

  IS-IS can be divided into areas, similar to OSPF's intra-area and inter-area routing. Routers can be configured as Level 1 (within an area), Level 2 (between areas), or Level 1-2 (both). 

• Designated Intermediate System (DIS):

  In broadcast networks, IS-IS uses a DIS to reduce the number of adjacencies and routing protocol traffic. The DIS acts as a representative for the broadcast network, exchanging routing information on its behalf. 

• Integrated IS-IS:

  IS-IS was initially designed for the OSI network layer protocol, but it has been extended to support IP (IPv4 and IPv6), leading to the term "Integrated IS-IS". 

• Scalability:

  IS-IS is known for its scalability, making it suitable for large and complex networks. 

How it works:

1. 1. Neighbor Discovery:

   IS-IS routers discover their neighbors by sending "hello" packets.

2. 2. Link-State Database:

   Once neighbors are discovered, routers exchange information about their directly connected links and other network topology information. This information is used to build a link-state database.

3. 3. Shortest Path Calculation:

   Each router uses the link-state database and Dijkstra's algorithm to calculate the shortest path to all reachable destinations.

4. 4. Routing Table:

   The calculated paths are installed in the routing table, and the router uses this table to forward traffic. 

IS-IS vs. OSPF:

While both are link-state IGPs, IS-IS and OSPF have some key differences:

• Protocol Design: IS-IS is based on the OSI standard, while OSPF is an IETF standard. 

• Area Structure: IS-IS areas are more flexible in terms of hierarchical structure compared to OSPF's backbone area. 

• Designated Router: IS-IS uses the term DIS (Designated Intermediate System), while OSPF uses Designated Router (DR). 

In Summary: IS-IS is a robust and scalable routing protocol widely used in large networks for efficient data forwarding. 

PATH VECTOR ROUTING PROTOCOL

A Path Vector Routing Protocol is a type of network routing protocol that uses path information to determine the best route for data packets.

It's primarily used for inter-domain routing, meaning it helps manage how data travels between different networks or organizations. Border Gateway Protocol (BGP) is the most well-known example of a path vector protocol. 

Key Concepts:

• Path Information:

  Instead of just sending the distance to a destination (like a distance vector protocol), path vector protocols send the entire path a packet needs to take to reach its destination. 

• Autonomous Systems (AS):

  In large networks like the internet, paths are often described as a series of autonomous systems, which are basically individual networks managed by different organizations. 

• Loop Prevention:

  By including the full path, these protocols can easily detect and prevent routing loops (where packets circulate endlessly). 

• Policy-Based Routing:

  Path vector protocols can also implement routing policies, allowing network administrators to choose specific paths based on factors like cost, security, or performance. 

How it Works:

1. 1. Path Advertisement:

   Routers running a path vector protocol exchange routing information, including the paths they know to various destinations. 

2. 2. Path Vector Creation:

   Each router adds its own identifier (like an AS number) to the path vector as it advertises it to its neighbors. 

3. 3. Loop Detection:

   If a router receives a path vector that includes its own identifier, it knows there's a loop and avoids using that path. 

4. 4. Path Selection:

   Routers choose the best path based on various criteria, often prioritizing paths with fewer AS hops or other policy-based rules. 

Example: BGP

Border Gateway Protocol (BGP) is the most widely used path vector protocol, particularly for routing between different internet service providers (ISPs). BGP ensures that data packets find their way across the vast and complex internet by tracking the paths through different networks. 

In Summary: Path vector protocols provide a robust and scalable way to manage routing in complex networks by including path information, preventing loops, and enabling policy-based routing. 

FIRST HOP REDUNDANCY PROTOCOL (FHRP)

FHRP is a networking protocol that provides redundancy for the default gateway on a network segment. It allows multiple routers to work together, so that if one fails, another automatically takes over, preventing network outages. 

Here's a more detailed explanation:

• Purpose:

  FHRP protocols are designed to eliminate single points of failure in a network's default gateway. If a router acting as the default gateway fails, the network would be disconnected, but with FHRP, a backup router takes over, ensuring continuous connectivity. 

• How it works:

  FHRPs create a virtual IP address that is shared by multiple routers. One router is designated as the active router (handling traffic), while others are in standby mode. If the active router fails, one of the standby routers takes over the virtual IP and begins forwarding traffic. 

• Key Protocols:

  • HSRP (Hot Standby Router Protocol): A Cisco-proprietary protocol. 

  • VRRP (Virtual Router Redundancy Protocol): An open standard protocol. 

  • GLBP (Gateway Load Balancing Protocol): A Cisco-proprietary protocol that provides load balancing among multiple routers. 

• Benefits:

  • Redundancy: Ensures continuous network connectivity by providing backup gateways. 

  • High Availability: Reduces downtime and increases the reliability of the network. 

  • Load Balancing: In some FHRP implementations (like GLBP), traffic can be distributed across multiple routers, improving performance. 

• Configuration:

  FHRPs typically involve configuring a virtual IP address and enabling the chosen protocol on the participating routers. 

• Example:

  If a computer's default gateway is the virtual IP address, and the active router fails, another router will automatically assume the virtual IP and continue forwarding traffic, preventing the computer from losing its connection. 

VIRTUAL IP ADDRESS (VIP)

A Virtual IP Address (VIP) is an ip address that isn’t tied to a specific physical network interface. Instead, it can be shared by multiple devices or "float" between them, primarily for redundancy and load balancing purposes.

It acts as a single point of contact for clients, directing traffic to different backend servers, or provides failover capabilities in case of a server outage. 

• Redundancy:

  VIPs enable failover. If one server in a pool goes down, the VIP can quickly switch to another available server, ensuring uninterrupted service. 

• Load Balancing:

  VIPs distribute incoming traffic across multiple servers, preventing any single server from being overwhelmed. 

• Connection Redundancy:

  VIPs provide a consistent IP address for clients even if the underlying physical servers change, making connections more robust. 

• Not Tied to a Physical Interface:

  Unlike regular IP addresses, VIPs are not directly assigned to a single network interface. 

• Used in Various Applications:

  VIPs are commonly used in high-availability setups, load balancers, and network address translation (NAT). 

How VIPs Work:

1. 1. Registration:

   VIPs are typically registered in a DNS (Domain Name System), a GNS (Grid Naming Service), or a hosts file. 

2. 2. Traffic Routing:

   When a client sends a request to a VIP, the network infrastructure directs the traffic to the appropriate server based on the VIP's configuration. 

3. 3. Failover Mechanism:

   In a high-availability setup, if a server with a VIP fails, the VIP is quickly reassigned to another server, and the client's connection is seamlessly redirected. 

Examples:

• High Availability:

  In a database cluster, a VIP can be used to represent the database, and if the primary database server fails, the VIP can be transferred to a backup server without interrupting user access. 

• Load Balancing:

  A web server cluster can use a VIP to distribute traffic across multiple web servers, ensuring that no single server is overloaded. 

• One-to-Many NAT:

  A VIP can be used to map a single public IP address to multiple private IP addresses, allowing multiple devices on a private network to share a single public IP address for internet access. 

In essence, a VIP is a clever networking technique that enhances reliability, scalability, and availability by abstracting the underlying physical network infrastructure from the client.