Working principle of layer 3 switch
30 2023-03-07

Layer 3 switching technology = Layer 2 switching + Layer 3 routing working principle

When the data is received by the port chip, the corresponding destination MAC address is first searched in the Layer 2 switching chip. If found, the Layer 2 forwarding is performed, otherwise the data is forwarded Sent to the Tier 3 engine.


In the three-layer engine, the ASIC chip searches the corresponding routing table information, compares it with the destination IP address of the data, and then sends the ARP data packet to the destination host to obtain the MAC address of the host , and sends the MAC address to the second-layer chip. The layer chip forwards the packet.


( 1 ) Traditional MLS
is also called network flow-based switching. The three-layer engine of the switch only needs to process the first data packet in the data flow, and all subsequent data is forwarded by the hardware (this method is called "one-time routing, multiple switching"), thus realizing three-layer switching wire-speed forwarding.


( 2 ) Based on the topology-based forwarding model of MLS based on CEF
, all routing information is added to the forwarding information base FIB in advance , and the switch can quickly search for IP adjacency, next-hop address and MAC address.