Routing Protocols: Distance Vector and Link State

• Routing protocols form the backbone of modern network communication
  • They facilitate efficient data travel across interconnected networks in various settings, from small home networks to large enterprise infrastructures
  • They ensure data packets reach their intended destinations through the most optimal paths
• Routing protocols dictate how routers communicate to exchange information about network topology
  • Enabling routers to dynamically adapt to changes, such as link failures or network congestion
  • This ensures reliable and efficient data delivery

Types of Protocols

• Distance Vector protocols use distance to figure out the best path for packets within a network
  • Measure distance based on the number of hops, which is the number of routers the data must pass through to reach its destination
• Link State protocols use Link State protocol to create three types of tables:
  • Neighbor table stores details of neighboring routers via the link state routing protocol
  • Topology table stores the whole network topology
  • Routing table stores the most efficient routes
• Interior Gateway Protocols (IGP) exchange routing information with other routers within a single autonomous system (AS).
  • An AS consists of one or more networks under the control of a single enterprise
  • The company AS is thus separate from the ISP AS
• Exterior Gateway Protocols (EGP) provides connectivity between different autonomous systems.
  • A uniform protocol connects different autonomous systems
  • Also known as an exterior gateway routing protocol.
• Classful protocols
• Classless Protocols

Interior Gateway Protocols (IGP) Examples

• Open Shortest Path First (OSPF)
• Routing Information Protocol (RIP)
• Intermediate System to Intermediate System (IS-IS)
• Enhanced Interior Gateway Routing Protocol (EIGRP)

Exterior Gateway Protocols (EGP) Examples

• Border Gateway Protocol (BGP)
• Exterior Gateway Protocol (EGP)
• The ISO's InterDomain Routing Protocol (IDRP)

Routing Information Protocol (RIP)

• RIP is one of the first routing protocols, used in both Local Area Networks (LANs) and Wide Area Networks (WANs)
  • Runs on the Application layer of the OSI model
  • Versions: RIPv1 and RIPv2
  • RIPv1 determines network paths based on the IP destination and hop count

RIP Pros

• Historical significance as one of the oldest routing protocols
• Operational simplicity; it is relatively straightforward to understand and implement
• Operation on the application layer makes it easy to manage and configure
• RIPv2's multicast capabilities allow efficient routing table communication, and enhanced security with authentication

RIP Cons

• Limited use in larger networks, has a maximum hop count of 15
• Lack of scalability, unsuited for modern expansive networks due to hop count limitation
• RIPv1's broadcasting method can lead to increased traffic and potential inefficiencies
• Use of hop count as the sole metric may not represent the best path in complex networks Slower convergence leads to potential temporary routing loops

Interior Gateway Protocol (IGRP)

• A distance vector routing protocol by Cisco
  • Designed to build on RIP to function more effectively within larger connected networks
  • Removed the 15 hop cap placed on RIP
  • Uses metrics such as bandwidth, delay, reliability, and load to compare the viability of routes within the network

IGRP Details

• Updates are broadcast every 90 seconds
• It has a maximum hop count of 255
  • Enables larger networks vs a protocol like RIP
• Resistant to routing loops; updates automatically when route changes occur

IGRP Pros

• Enhanced scalability due to the maximum hop count of 255, suitable for larger networks
• Multiple Metrics: Improved routing decisions using bandwidth, delay, reliability, and load metrics
• Frequent Updates: Network is well-informed and up-to-date via updates every 90 seconds
• Loop Resistance: Built-in features automatically update routes, reducing routing loops
• Cisco Legacy: Developed by Cisco, benefits from being backed by one of the industry leaders

IGRP Cons

• Proprietary Protocol: Not universally adaptable across all devices from different manufacturers, being a Cisco product
• The Limited Default Metrics mean that only bandwidth and delay are considered under default settings
• Potentially overlooking other valuable information
• Superseded by EIGRP: IGRP has been replaced by Enhanced IGRP (EIGRP), which offers more advantages
• Diminished use in modern networks
• Larger Overhead: it can generate more network overhead compared to simpler protocols like RIP
• Potential Complexity: Configuration and troubleshooting more complex than simpler protocols due to multiple metrics

Open Shortest Path First (OSPF)

• A link-state IGP tailored for IP networks using the Shortest Path First (SPF) algorithm
  • SPF routing algorithm is used to calculate the shortest path spanning-tree for efficient data transmission of packets
  • Routers maintain databases of the network's surrounding topology filled with data from Link State Advertisements (LSAs) from other routers
• Uses the Dijkstra algorithm to recalculate network paths when the topology changes
  • Is considered relatively secure, since it can authenticate protocol changes to keep data secure
  • Used by many organizations because it's scalable to large environments, the topology changes are tracked, and OSPF can recalculate compromised packet routes if a previously-used route has been blocked

OSPF Pros

• Efficient Routing: Utilizes the Shortest Path First (SPF) algorithm to ensure optimal data packet transmission
• Detailed Network Insight: Routers maintain a database on the network's topology, offering a detailed perspective on its structure
• Dynamic Adaptability: Employs the Dijkstra algorithm to dynamically adjust to network topology changes, ensuring continuity in data transmission
• Security Features: protocol change authentication to maintain data security, ensuring that only authorized updates are made
• Highly Scalable: Suitable for both small and large-scale network environments, making it versatile for various organizational sizes

OSPF Cons

• Complex Configuration: Given its many features, OSPF can be complex to set up and maintain
• Higher Overhead: Maintaining detailed databases and frequently recalculating routes can generate more network overhead
• Sensitive to Topology Changes: Frequent topology alterations can cause performance dips as it recalculates routes
• Resource Intensive: OSPF routers require more memory and CPU resources due to their database maintenance and route recalculations
• Potential for Large LSDB: In very large networks, the Link State Database (LSDB) can grow significantly, necessitating careful design and segmenting

Exterior Gateway Protocol (EGP)

• A protocol used to exchange data between gateway hosts that neighbor each other within autonomous systems
  • It provides a forum for routers to share information across domains
  • A high profile example is the internet itself
• EGP's routing table includes known routers, route costs, and network addresses of neighboring devices. EGP was widely-used by larger organizations but has since been replaced by BGP
• Does not support multipath networking environments
• It works by keeping a database of nearby networks and the routing paths to reach them. That route information is sent to connected routers
  • Whereupon devices can update their routing tables and undertake more informed path selection

EGP Pros

• Allows gateway hosts to share information across distinct network domains, effectively acting as a bridge between autonomous systems
• a precursor and essential component to the modern internet's formation
• Contains comprehensive information, including known routers, route costs, and addresses of neighboring devices in its routing database
• Route data is sent to neighboring routers to help them update their tables and make better routing decisions

EGP Cons

• Lacks multipath support and isn't suitable for modern multipath networking environments
• Is considered obsolete, since it has been largely phased out in favor of more advanced protocols such as BGP
• Has limited scalability, since EGP struggled with handling larger and more intricate systems as networks grew
• Employs Static Path Determination, while EGP keeps a database of nearby networks, its path determinations are more static, making it less flexible than newer protocols
• Potential for Redundancy, with EGP's method of sharing all route data with neighboring routers can lead to redundant data transmission and larger routing tables

Border Gateway Protocol (BGP)

• The routing protocol of the internet and is classified as a distance path vector protocol
  • Designed to replace EGP with a decentralized approach to routing
  • The BGP Best Path Selection Algorithm selects the best routes for data packet transfers
  • Without custom settings, it will select routes with the shortest path to the destination.
• Administrators tend to change the routing decisions according to criteria in line with their needs
  • Customizable by changing the BGP cost community attribute
  • Factors that affect routing decisions include weight, local preference, locally generated, AS_Path length, origin type, multi-exit discriminator, eBGP over iBGP, IGP metric, router ID, cluster list and neighbor IP address

BGP Pros

• Internet Backbone; as the primary routing protocol, it plays a pivotal role in global data exchanges
• Is characterized by a Decentralized Design; unlike EGP, BGP ensures for more robust and adaptable network operations
• Offers a Customizable Path Selection; through the BGP's Best Path Selection Algorithm, you can tailor to meet unique network by adjusting attributes
• Provides for Efficient Updates; which reduces unnecessary network traffic by only transmitting updates when there's a change
• Grants Granular Routing Decisions, by letting administrators use factors like weight, AS_Path length, and IGP metric to inform routing decisions, allowing for a high degree of routing precision
• Secures with Authentication, since authentication measures are provided that enhances the security of routing updates by allowing only authorized routers to participate in data exchanges.

BGP Cons

• It requires meticulous manual configuration, since, unlike EGP, it does not self-discover topology changes
• Mistakes or malicious actions in BGP configurations can inadvertently or intentionally divert internet traffic, potentially leading to large-scale outages contributing towards Potential Instability
• Given Internet growth, BGP's current scalability might pose challenges
• Although it has Authentication measures, BGP is historically susceptible to certain security issues such as prefix hijacking contributing towards Vulnerabilities
• Calls for a higher Learning Curve, because there can be a mastery challenging to many network administrators
• It has a Convergence Time, that can make it take longer to converge after a network change

Intermediate System-to-Intermediate System (IS-IS)

• IS-IS is a link-state, IP routing protocol and IGPP protocol used on the internet to send IP routing information
  • It uses a modified version of the Dijkstra algorithm
• Network consists of end systems, intermediate systems (routers), areas, and domains
  • Organized into groups called areas, then multiple areas are grouped together to make up a domain
  • Routers within the area are placed with Layer 1 and routers that connect segments together are classified as Layer 2
  • Addresses used include: Network Service Access Point (NSAP) and Network Entity Title (NET)

IS-IS Pros

• Provides a Hierarchical Design with simplification of management and optimizes routing in large networks, since it organizes routers into areas and domains.
• It has Scalability because it allows for efficient operation in large-scale networks and allows for the skipping of unnecessary routing overhead, since it implements a division into areas and domains
• It has Flexibility allowing adaptability to different architectures of networks in virtue of no exclusive connection for the use of IP only
• It guarantees Efficient Path Selection in virtue of utilizing a modified version of the Dijkstra algorithm for optimal path determination.
• It provides a Distinct Addressing Mechanism, being that there are unique addresses like NSAP and NET, IS-IS provides granularity in addressing which can assist in network troubleshooting and management.
• It provides for a Dual-Level of Operation; in that the segregation of intra-area routings are separate from inter-area routings, by implementation of a Layer 1 and Layer 2 classification, which causes to simplify router roles and ensures efficiency of routing.

IS-IS Cons

• Because of a new terminology and addressing mechanism in which masters might not be familiar, IS-IS might pose a challenge for network engineers
• The Address Length can be long which may complicate both manual configuration and troubleshooting, since the NSAP address can have a certain length
• The Lesser Adoption can cause concerns to leading to inter-compatibility needs; it is a lesser use to the internet relative to the OSPF
• It has a Complex Nature of the Configuration that is rooted in the implementation of a hierarchical structure, as opposed to simple IS-IS configurations; which causes a more challenging configuration but a great and effective scaling benefit.
• ISO OSI model roots, that can cause problems in certain interoperability concerns when you are trying to implement with something like an IP-based IS-IS protocol
• The evolution might not always be best in IP based tasks; the origins is ISO in the model which causes for some tasks and protocols it might lack some specific tasks such as a newer protocol usage in tasks and situations

Enhanced Interior Gateway Routing Protocol (EIGRP)

• A distance vector routing protocol used for IP, AppleTalk, and NetWare networks
• A Cisco proprietary protocol designed as a follow on from the original IGRP protocol
• When using it, a router takes information from its neighbors' routing tables and records it
  • Neighbors are queried for a route, and when a change occurs the router notifies its neighbors about the change
  • The end result is neighboring routers are aware of what is going on in nearby devices
• Equipped with features to maximize efficiency, including Reliable Transport Protocol (RTP) and a Diffusing Update Algorithm (DUAL)
  • Packet transmissions are made more effective because routes are recalculated to speed up the convergence process

EIGRP Pros

• Can support multiple network protocols, including IP, AppleTalk, and NetWare for its Versatility
• Successor to the original design of the IGRP it has been built with a design to have more features when being used to route different packets with advanced designs
• By making a design that collects data from different neighbor routing tables, EIGRP manages a real-time understanding of all network environments from collection and management of other neighbors, which makes an exchange between connections faster
• There is an update to informing routers quickly such as routers that inform neighbors that have changes and updates to promote and foster the environment by notifying a fast responsiveness
• The reliability promotes packet based transmission and acknowledges receipt of its routing updates through means and systems
• A route is now calculated and will result in network changes, and can reduce the amounts of taking the time needed to stabalize and be used for improvements and changes made in the DUAL and related networks that have been incorporated

EIGRP Cons

• The system is a mix and can be used to test equipment which might cause it to limit interoperbility
• Proprietary to the Protocol and Cisco specifically in which may be a cause as part for implementation
• The Overhead is frequent in all routing exchanges such in queries that must be run frequently as well especially on large networks while being used for resourcess which makes up a cause for bandwidth consuming
• Has possible complex configurations that are set to steep learning that can be powerful configurations if used correctly to the proper specific needs in what you must perform