Routing Table
Routing Table is a data structure used by routers to store and manage route information. It determines the best path for forwarding packets to their destination. Each entry in a routing table corresponds to a specific destination network and includes information about the next hop, metrics, and routing protocol.
Overview[edit | edit source]
The routing table is a fundamental component of the control plane in a network. It is built and maintained by routing protocols or through manual configuration. Routers use the routing table to make forwarding decisions and update the forwarding table in the data plane.
Structure[edit | edit source]
A typical routing table contains the following fields:
- Destination Network: The IP address range or subnet for the route.
- Subnet Mask: Specifies the size of the destination network.
- Next Hop: The IP address of the next router or device along the path.
- Metric: A value representing the cost of the route (e.g., hop count, delay, bandwidth).
- Interface: The local network interface to use for forwarding packets.
- Routing Protocol: Indicates the protocol (e.g., OSPF, BGP) that added the route.
Example Routing Table:
| Destination Network | Subnet Mask | Next Hop | Metric | Interface | Protocol |
|---|---|---|---|---|---|
| 192.168.1.0 | 255.255.255.0 | 10.0.0.1 | 1 | eth0 | OSPF |
| 10.0.0.0 | 255.0.0.0 | 10.0.1.1 | 10 | eth1 | BGP |
| 0.0.0.0 | 0.0.0.0 | 192.168.1.254 | 5 | eth0 | Static |
Types of Routes[edit | edit source]
Routing tables include different types of routes based on how they are learned:
- Static Routes: Manually configured by network administrators.
- Dynamic Routes: Automatically learned and updated using routing protocols (e.g., RIP, OSPF, BGP).
- Default Routes: Used when no specific match is found in the routing table; often represented as 0.0.0.0/0.
- Connected Routes: Directly connected networks that the router is aware of.
How It Works[edit | edit source]
- When a packet arrives, the router examines its destination IP address.
- The router searches the routing table for the most specific matching route using techniques like Longest Prefix Matching.
- Once a match is found, the packet is forwarded to the next hop or local interface specified in the route.
Dynamic Routing Protocols[edit | edit source]
Routing tables are dynamically populated and maintained by various protocols:
- RIP (Routing Information Protocol): Uses hop count as a metric.
- OSPF (Open Shortest Path First): Calculates the shortest path using Dijkstra's algorithm.
- BGP (Border Gateway Protocol): Exchanges routing information across autonomous systems.
- EIGRP (Enhanced Interior Gateway Routing Protocol): Uses a composite metric of bandwidth and delay.
Applications[edit | edit source]
- Enterprise Networks: Routing tables guide traffic between different subnets and external networks.
- Service Providers: Manage large-scale routing across wide-area networks.
- Data Centers: Used to ensure efficient routing in complex, multi-tier architectures.
Advantages[edit | edit source]
- Provides efficient and automated routing decisions.
- Adapts dynamically to network changes using routing protocols.
- Scalable for networks of varying sizes and complexities.
Limitations[edit | edit source]
- Large routing tables can consume significant memory and CPU resources.
- Incorrect routing table entries can lead to routing loops or blackholes.
- Static routes require manual updates, which can be error-prone in dynamic networks.
