Editing Multilayer switch (section)

==Multilayer switch==
Multi-layer switching combines layer-2, -3 and -4 switching technologies and provides high-speed scalability with low latency. Multi-layer switching can move traffic at [[wire speed]] and also provide layer-3 routing. There is no performance difference between forwarding at different layers because the routing and switching are all hardware-based{{snd}}routing decisions are made by specialized [[application-specific integrated circuit]]s (ASICs) with the help of [[content-addressable memory]].<ref name=switchoperation />

Multi-layer switching can make routing and switching decisions based on the following
* [[MAC address]] in a data link frame
* Protocol field in the data link frame
* IP address in the [[network layer]] header
* Protocol field in the network layer header
* Port numbers in the [[transport layer]] header

MLSs implement [[quality of service|QoS]] in hardware. A multilayer switch can prioritize [[packet (information technology)|packet]]s by the 6 bit [[differentiated services code point]] (DSCP). These 6 bits were originally used for [[type of service]]. The following 4 mappings are normally available in an MLS:{{citation needed|date=January 2019|reason=Some inspection is limited to DSCP. Some can map direct from DSCP to queue. Many can map from port number to DCSP/802.1p. There's a good range of "normal" in this area and no citation to support this particular list.}}
* From OSI layer 2, 3 or 4 to IP DSCP (for IP packets) or [[IEEE 802.1p]]
* From IEEE 802.1p to IP DSCP
* From IP DSCP to IEEE 802.1p
* From VLAN IEEE 802.1p to port egress queue.

MLSs are also able to route IP traffic between [[VLAN]]s like a common [[router (computing)|router]]. The routing is normally as quick as switching (at wire speed).