layer 3 switch


Also found in: Dictionary, Thesaurus, Legal.

layer 3 switch

A network device that forwards traffic based on layer 3 information at very high speeds. Traditionally, routers, which inspect layer 3, were considerably slower than layer 2 switches. In order to increase routing speeds, many "cut-through" techniques were used, which perform an "inspect the first packet at layer 3 and send the rest at layer 2" type of processing. Ipsilon's IP Switch and Cabletron's SecureFast switches were pioneers in cut-through switching.

From Software to Hardware
As more routing lookup functions were moved from software into the ASIC chips, layer 3 switches could inspect each packet just like a router at high speed without using proprietary cut-through methods. If a layer 3 switch supports packet-by-packet inspection and supports routing protocols, it is called a "routing switch" or "switch router," which simply means "fast router." For example, Cisco calls its high-end routers Gigabit Switch Routers.

More Inspection Takes Time
The more deeply a packet is examined, the more forwarding decisions can be made based upon type of traffic, quality of service (QoS) and so on. To obtain this information requires digging into the packet's headers to ferret out the data, which takes processing time. To understand how packets are formed, see TCP/IP abc's. The following shows which data are examined at each layer. See layer 3, layer 2 switch, Web switch and virtual LAN.

TCP/IP SWITCHING/ROUTING DECISIONSLayer and      ForwardingProtocol       DecisionInspected      Based on

  2 - Ethernet   MAC address

  3 - IP         Network address
  3 - IP         Service quality

  4 - TCP/UDP    Traffic type
      socket     (HTTP, FTP, etc.)

  7 - HTTP       HTTP request type



Enterprise-class Layer 3 Switch
The BlackDiamond 6800 provided a non-blocking backplane for switching 48 million packets per second. It provided wire-speed IP routing at layer 3 and wire-speed switching at layer 2. (Image courtesy of Extreme Networks, www.extremenetworks.com)








Enterprise Class and No Layers
In 1886, this 50-line magneto switchboard, made by Bell Telephone of Canada, was used to switch voice conversations in small localities. These instruments forged a world of switches and routers that forward billions of calls and data packets every day. (Image courtesy of Nortel Networks.)
References in periodicals archive ?
However, Cabletron senior architect Trent Waterhouse says that "some people are saying MPOA will be dead on arrival." The reason, according to Waterhouse, is that network vendors figured out how to apply to new Layer 3 switches the lessons of ASICs in Layer 2 switches.
3Com product manager Glen Gibson says "FastIP is not being positioned as the best solution for new installations, areas which are now being addressed by Layer 3 switches, which offer higher performance and more features."
Using Layer 3 switches to route between ELANs is preferable to early, software-only implementations of MPOA.
One of the key areas of innovation available today in higher-end enterprise switching systems is the ability to extend the advanced features and services of the Layer 3 switches into the wireless domain through distributed application of network policy.
The new 100BaseFX modules for BigIron Layer 3 switches allow Metro service providers to extend broadband Ethernet connectivity over single mode fiber for long reach of up to 40 kilometers while taking advantage of the density and low cost of 100 Mbps Ethernet.
Delivering up to 120 Gigabit Ethernet ports and 178,000,000 packets per second (pps) non-blocking performance, Foundry's BigIron Layer 3 switches are 10 Gigabit capable so that as Internet traffic increases, with the introduction of Broadband access, MIX can provide the necessary scalability to meet future demands.
POS-PHY Level 3 is the industry standard for 2.5 Gbit/s OC-48 and multi-channel 622-Mbit/s OC-12 transmission rates required by the new generation of super routers and layer 3 switches for multi-service voice and data networks.
Dacom, a Korean common carrier network service provider, has deployed Foundry's BigIron Layer 3 switches and ServerIron Internet traffic and content management switches to enhance its metropolitan network's reliability, performance and capability.
Layer 3 switches, for example, use information from the network layer, or Level 3 of the OSI model, to route packets at wire speed, raising performance to the millions-of-packets-per-second range, compared with thousands of packets per second with software routers.
Worldwide Layer 3 switches represented 1.35 million ports and $825 million in revenue in 3Q99.
TELECOMWORLDWIRE--(C) 1994-8 M2 COMMUNICATIONS LTD PMC-Sierra has launched a new Packet-Over-SONET/SDH physical interface specification, called POS-PHY Level 3, which has been endorsed by the SATURN POS Group and allows up to 3.2Gb/s throughput, enabling high-speed POS interfaces for emerging super routers and layer 3 switches.