layer 4

layer 4

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layer 4 switch

A network device that integrates routing and switching by forwarding traffic at layer 2 speed using layer 4 and layer 3 information. When packets are inspected at layer 4, the sockets can be analyzed and decisions can be made based on the type of application being serviced. See layer 4-7, layer 3 switch and Web switch.

layer 4-7

The two layers in a network packet that identify its content (for details about layers, see TCP/IP and OSI model). The bottom layers 1, 2 and 3 are the protocols that move a network packet from source to destination. Layers 4 and 7 identify the application that created the packets as well as the specifics of the request. For example, inspecting layer 4 can identify HTTP traffic (Web traffic), but inspecting layer 7 can determine what the HTTP request is for (see Web switch). See layer 4 switch and well-known port.


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

transport layer

The processing in a network protocol that provides end-to-end management. The transport layer is layer 4 of 7 in the OSI model, and it may or may not guarantee error-free delivery depending on the specific protocol used. See transport protocol, TCP/IP and OSI model.

transport protocol

A communications protocol responsible for establishing a connection and ensuring that all data has arrived safely. It is defined in layer 4 of the OSI model. Often, the term transport protocol also implies transport services, which includes the lower-level data link protocol that moves packets from one node to another. See TCP/IP, OSI model and transport services.
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References in periodicals archive ?
Layer 4 is user- and account-centric across multiple channels and products.
These test results were based on Layer 4 throughput rates rather than the more-typically quoted Layer 1 payload rates.
Let's play the networking technology name game: If Layer 2 switching is fast, and Layer 3 switching is fast and scalable, then it stands to reason that Layer 4 switching must be the next big thing in switching.
The problem, though, is that Layer 4 switching does not exist - and it never will.
The attraction to vendors of Layer 4 switching is irresistible: the Layer 2 (LAN) switch market exploded because these switches inexpensively micro-segmented LANs, thus providing vast performance improvements at a fraction of the cost of routers.
Both of these developments started the 'name game' that now appears to culminate with Layer 4 switching (if not, then be on the look out for Layer 7 switching !).
In networks today, Layer 4 information can play a crucial role in influencing how a switch forwards traffic.
Now, imagine you are a Layer 4 switch sitting in the middle of the network and you must make forwarding decisions based exclusively on Layer 4 information.
Most likely, switch vendors will integrate Layer 4 load balancing functionality into their switch products.
This brings us to the first evolution of switches and load balancing, which involves the integration of Layer 4 load balancing directly onto the switch.
ECV (Extended Content Verification) and EAV (Extended Application Verification) server health checking (though TCP/UDP application port checking is included in the Layer 4 capability)
One might ask: Why not simply embed Layer 7 technology into a switch, similar to the integration of Layer 4? Basically, Layer 7 is tightly integrated with the application infrastructure and specialized application Layer 7 functionality is more appropriately delegated to an appliance-based device than to a switch.