While learning networking concepts I learn a network hardware port can be switch port to carry MAC headers or Routed port to carry L3 info.

However, Cisco MLS concepts as I understand a switch port can carry both MAC and Layer 3

Can someone explain this?

Thanks in advance

  • Since layer-3 packets are encapsulated inside layer-2 frames, any port carrying layer-2, by definition, also carries layer-3.
    – Ron Maupin
    Feb 23 '16 at 23:06
  • @RonMaupin thanks for your response..is there a Cisco config as example to understand?
    – discovery
    Feb 23 '16 at 23:08
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 7 '17 at 19:57

Even with Cisco MLS, each port is defined as a layer-2 switch port (with the switchport command) or a layer-3 router port (with the no switchport command). You can have virtual ports call SVIs for the VLANs of which the layer-2 switch ports are members.

In essence, a layer-3 switch is a layer-2 switch with built-in layer-3 routing. Remember that it is still a layer-2 switch, and the routing features may fall short of what you get with a dedicated router. You will also find hardware not normally associated with LAN switching (e.g., WAN ports) unavailable for most layer-3 switches.

Cisco has moved routing features in hardware (ASICs) to ease the processor and memory requirements normally associated with routing. A simple search of the Internet for cisco mls turns up a lot of hits, including Multilayer Switching Overview:

MLS provides high-performance Layer 3 switching for Cisco routers and switches. MLS switches IP data packets between subnets using advanced application-specific integrated circuit (ASIC) switching hardware. Standard routing protocols, such as Open Shortest Path First (OSPF), Enhanced Interior Gateway Routing Protocol (Enhanced IGRP), Routing Information Protocol (RIP), and Intermediate System-to-Intermediate System (IS-IS), are used for route determination.

You will also find hits with links to Cisco documentation on how to configure MLS, including examples.

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