Forwarding Table

IT 위키

Forwarding Table is a data structure used by network devices, such as routers and switches, to determine the next hop or output interface for forwarding packets. It plays a crucial role in the data plane, enabling efficient and accurate packet forwarding based on precomputed rules.

Overview[편집 | 원본 편집]

The forwarding table maps packet header information, such as destination IP addresses or MAC addresses, to specific output ports or next-hop devices. It is typically built using information from the routing table (in the control plane) and other protocols, such as ARP (Address Resolution Protocol) or VLAN tagging.

Key Features[편집 | 원본 편집]

  • High-Speed Lookup: Forwarding tables are optimized for rapid lookup operations to meet real-time data forwarding requirements.
  • Compact Representation: They use efficient data structures, such as trie-based trees or hash tables, to minimize memory usage.
  • Dynamic Updates: Forwarding tables are updated dynamically as network conditions change, such as when routes are added or removed.

Structure[편집 | 원본 편집]

A typical forwarding table entry includes:

  • Destination Address: The destination IP or MAC address of the packet.
  • Prefix Length: In IP forwarding, this indicates the subnet or network range.
  • Next Hop: The address or identifier of the next device in the path.
  • Output Interface: The network interface through which the packet should be forwarded.
  • Metric (Optional): A value indicating the cost of the route, used for decision-making in multi-path scenarios.

Example Forwarding Table:

Destination Network Prefix Length Next Hop Output Interface
192.168.1.0 24 10.0.0.1 eth0
10.0.0.0 16 10.0.1.1 eth1
0.0.0.0 0 10.0.2.1 eth2

Relationship to Routing Table[편집 | 원본 편집]

  • The routing table exists in the control plane and stores all potential routes learned from routing protocols or static configurations.
  • The forwarding table is derived from the routing table and is used in the data plane for real-time packet forwarding.
  • Forwarding tables are smaller and optimized for lookups compared to routing tables, which store more extensive information.

Applications[편집 | 원본 편집]

  • Routers: Forwarding tables guide IP packets to the appropriate next hop in a routed network.
  • Switches: Used for MAC address forwarding in Layer 2 networks.
  • SDN Devices: Forwarding tables are dynamically programmed by the SDN controller to implement specific traffic policies.

Advantages[편집 | 원본 편집]

  • Ensures efficient and accurate packet delivery.
  • Reduces complexity by abstracting real-time forwarding decisions.
  • Supports scalability by maintaining only active paths and routes.

Limitations[편집 | 원본 편집]

  • Requires constant synchronization with the routing table to handle network changes.
  • High-speed lookups can be resource-intensive in large-scale networks.
  • Forwarding tables are specific to the data plane and cannot make high-level routing decisions.

See Also[편집 | 원본 편집]