Hierarchical routing tackles scalability issues in large networks by dividing them into manageable domains. It reduces routing table size, improves performance, and enhances stability. This approach is crucial for handling the complexity of modern networks.
Border Gateway Protocol (BGP) plays a key role in hierarchical routing, enabling communication between autonomous systems. It facilitates the exchange of network reachability info, supports policy-based routing, and allows for route aggregation, making it essential for Internet backbone routing.
Hierarchical Routing
Need for hierarchical routing
- Scalability challenges arise in large networks as the number of devices and connections increase
- Routing tables grow larger requiring more storage space and processing power for routers to handle
- Network convergence slows down due to the increased complexity and number of routes to process
- Hierarchical routing improves scalability by dividing the network into smaller, manageable domains (regions, areas)
- Reduces the size of routing tables by aggregating routes within each domain
- Enhances network performance and stability by localizing the impact of network changes and failures
Autonomous systems in routing
- An autonomous system (AS) is a collection of networks managed by a single administrative entity (organization, company)
- Each AS operates with its own internal routing policies and protocols (OSPF, EIGRP)
- ASes connect to each other to enable inter-domain routing and facilitate communication between different networks
- Hierarchical routing leverages ASes to achieve scalability by hiding internal network details from other ASes
- Routes within an AS can be aggregated before being advertised to other ASes, reducing the amount of routing information exchanged
Border Gateway Protocol (BGP)
Purpose of border gateway protocol
- BGP is an exterior gateway protocol (EGP) designed for routing between different autonomous systems
- Enables the exchange of network reachability information among BGP routers in different ASes
- Allows each AS to advertise its network prefixes and learn about routes to other ASes
- Facilitates the establishment of a logical routing topology between ASes, forming the backbone of the Internet
Key features of BGP
- Path vector routing protocol that propagates the best path to reach a destination based on various attributes
- Attributes include AS_PATH (list of ASes traversed), LOCAL_PREF (preferred path within an AS), MULTI_EXIT_DISC (suggested entry point into an AS), and ORIGIN (source of the route information)
- Supports policy-based routing, allowing administrators to control route selection and advertisement based on their specific requirements (security, performance, business relationships)
- Enables route aggregation, combining multiple specific routes into a single, less specific route to reduce routing table size
- Provides mechanisms for route filtering and manipulation to enforce routing policies and maintain network stability
Advantages of hierarchical routing
- Improves scalability by reducing the size of routing tables through route aggregation and hiding internal network details
- Enables efficient inter-domain routing between autonomous systems, allowing for the exchange of reachability information
- Enhances network stability and performance by minimizing the impact of network changes and failures within each AS
- Speeds up network convergence compared to flat routing architectures, as changes are localized within each domain
- Offers flexibility in defining and enforcing routing policies based on various attributes and business requirements
- Simplifies network management by dividing the network into smaller, manageable domains (ASes) for easier troubleshooting and maintenance