01. What Is a Router?

• Routing: Determines the path a data packet takes from the source to the destination (the optimal transmission path between hosts). This process is called routing.
• Forwarding: Transfers data packets from the router’s input port to the appropriate output port (this happens internally within the router).

02. Typical Router Structure

03. How a Router Works

1. Routing (Software, Control Layer):
   • The routing protocol selects and generates routing entries, which are added to the routing table.
   • The routing table is mapped into the forwarding engine in memory and stored in the cache area of the ASIC chip.

2. Packet Forwarding (Hardware, Data Layer):
   • After the data link layer removes the frame header and trailer, the packet is sent to the network layer.
   • The network layer uses the IP header’s key fields to search the forwarding table and determine the output interface.

04. Hardware Routing Forwarding Table

• CAM Table:
  • Performs binary matching (1 or 0). It either fully matches or does not match at all.
  • Used for MAC address lookups.

• TCAM Forwarding Table:
  • Performs ternary matching (0, 1, or “don’t care”).
  • Sorted from precise to imprecise matches.
  • Used for routing table policies, routing matches, firewalls, and routing rule matching.

05. NP (Network Processor) Chip

• Higher Performance: Integrates dozens of CPUs, hardware co-processors, and accelerators. Even with complex QoS functions like congestion management and queue scheduling, it can still achieve line-speed forwarding (“hard forwarding”).
• Greater Flexibility: Programmable user interfaces allow for flexible expansion.
• Strong Service Support: Quickly supports new value-added services (e.g., MPLS, QoS, multicast).
• Convenient Management and Development: Significantly shortens the secondary development cycle.
• IPv6 Compatibility: Reserved IPv6 interfaces allow for smooth software upgrades.
• High Reliability: Chips undergo rigorous fatigue testing before production, making them suitable for telecom-grade equipment development.

06. Multi-Stage Switching Structure Routers

07. Cluster Routers

• The switching structure aggregates multiple switching structures, offering a distributed architecture that meets performance, scalability, and size requirements.
• It includes multiple control nodes with routing computation capabilities, enabling distributed implementation of routing and control protocols.
• The cluster router architecture is considered the next-generation high-performance router architecture that aligns with the needs of internet development.