The various functions of network devices can be logically divided into ‘planes’. There are three such planes commonly referred to in the networking industry:
Data Plane
All functions involving forwarding user data from one interface to another are in the Data Plane.
Example
- A router receives a message, looks for the most specific matching route in its routing table, and forwards it out of the appropriate interface to the next hop/destination.
- A switch receives a message, looks at the destination MAC, and forwards it out of the appropriate interface(s).
The Data plane is also sometimes called the ‘Forwarding plane’.
Control Plane
Functions that control the data plane, or which build the resources used to control the data plane (e.g. routing tables, ARP tables, STP, etc.) are part of the Control Plane.
The control plane consists of overhead work, e.g. OSPF doesn’t actually forward any data, but it instructs the data plane about how packets are to be forwarded.
The control plane is distributed, i.e. each device has its own localized control plane.
Management Plane
Like the control plane, the Management Plane performs overhead work. However, the management plane doesn’t directly affect the forwarding of messages in the data plane.
As the name implies, the management plane consists of protocols used to manage devices, e.g. SSH/Telnet, Syslog, SNMP, NTP, etc.
You can think of the management plane as controlling the control plane, which in turn controls the data plane.
ASICs, a note
While the operations of the Control & Management planes are performed by a device’s CPU, the Data plane is not. This is because CPUs, while versatile, are relatively slow. Data plane operations need to be performed as fast as possible for maximum bandwidth, so specialized hardware called ASICs (Application-Specific Integrated Circuits) are used.
These chips are designed for a single purpose, to be completed with the highest possible speed and efficiency.
In the case of switches, for example, when frames are received the forwarding decision is made by an ASIC. The MAC address table is stored in a specialized type of memory called TCAM (Ternary Content-Addressable Memory), which allows for very fast address lookups. Because of the use of TCAM, another common name for a MAC address table is the CAM table.
Most routers will use a similar hardware configuration: routing decisions being made with an ASIC and tables stored in TCAM.
Info
While ASICs are standard for network hardware, technically there’s nothing an ASIC does that a CPU couldn’t do — CPUs are just a lot slower.
It is possible to make a typical desktop computer act as a switch or router, assuming it has multiple network interfaces, and some hobbyists and home-labbers do, though it’s not viable in an enterprise setting.