Layer-specific functionality Network switch

1 layer-specific functionality

1.1 layer 1 (hubs vs. higher-layer switches)
1.2 layer 2
1.3 layer 3
1.4 layer 4
1.5 layer 7

layer-specific functionality


a modular network switch 3 network modules (a total of 24 ethernet , 14 fast ethernet ports) , 1 power supply.

while switches may learn topologies @ many layers, , forward @ 1 or more layers, tend have common features. other high-performance applications, modern commercial switches use ethernet interfaces.

at layer, modern switch may implement power on ethernet (poe), avoids need attached devices, such voip phone or wireless access point, have separate power supply. since switches can have redundant power circuits connected uninterruptible power supplies, connected device can continue operating when regular office power fails.

layer 1 (hubs vs. higher-layer switches)

a network hub, or repeater, simple network device not manage of traffic coming through it. packet entering port flooded out or repeated on every other port, except port of entry. specifically, each bit or symbol repeated flows in (with minimum delay line interface). due this, repeater hub can receive , forward @ single speed. since every packet repeated on every other port, packet collisions affect entire network, limiting overall capacity.

there specialized applications in network hub can useful, such copying traffic multiple network sensors. high-end network switches have feature called port mirroring provides same functionality.

a network switch creates layer 1 end-to-end connection virtually, while mandatory. bridging function of switch uses information taken layer 2 select each packet particular port(s) has forwarded to, removing requirement every node presented traffic. result, connection lines not switched literally, instead appear way on packet level.

by 2000s, there little price difference between hub , low-end switch.

layer 2

a network bridge, operating @ data link layer, may interconnect small number of devices in home or office. trivial case of bridging, in bridge learns mac address of each connected device. bridges buffer incoming packet , adapt transmission speed of outgoing port.

classic bridges may interconnect using spanning tree protocol disables links resulting local area network tree without loops. in contrast routers, spanning tree bridges must have topologies 1 active path between 2 points. older ieee 802.1d spanning tree protocol quite slow, forwarding stopping 30 seconds while spanning tree reconverged. rapid spanning tree protocol introduced ieee 802.1w. newest standard shortest path bridging (ieee 802.1aq) next logical progression , incorporates older spanning tree protocols (ieee 802.1d stp, ieee 802.1w rstp, ieee 802.1s mstp) blocked traffic on 1 alternative path. ieee 802.1aq (shortest path bridging spb) allows paths active multiple equal cost paths, provides larger layer 2 topologies (up 16 million compared 4096 vlans limit), faster convergence, , improves use of mesh topologies through increased bandwidth , redundancy between devices allowing traffic load share across paths of mesh network.

while layer 2 switch remains more of marketing term technical term, products introduced switches tended use microsegmentation , full duplex prevent collisions among devices connected ethernet. using internal forwarding plane faster interface, give impression of simultaneous paths among multiple devices. non-blocking devices use forwarding plane or equivalent method fast enough allow full duplex traffic each port simultaneously.

once bridge learns addresses of connected nodes, forwards data link layer frames using layer 2 forwarding method. there 4 forwarding methods bridge can use, of second through fourth methods performance-increasing methods when used on switch products same input , output port bandwidths:

while there specialized applications, such storage area networks, input , output interfaces same bandwidth, not case in general lan applications. in lans, switch used end user access typically concentrates lower bandwidth , uplinks higher bandwidth.

layer 3

within confines of ethernet physical layer, layer-3 switch can perform or of functions performed router. common layer-3 capability awareness of ip multicast through igmp snooping. awareness, layer-3 switch can increase efficiency delivering traffic of multicast group ports attached device has signalled wants listen group.

layer 4

while exact meaning of term layer-4 switch vendor-dependent, starts capability network address translation, adds type of load distribution based on tcp sessions.

the device may include stateful firewall, vpn concentrator, or ipsec security gateway.

layer 7

layer-7 switches may distribute load based on uniform resource locators (urls), or using installation-specific technique recognize application-level transactions. layer-7 switch may include web cache , participate in content delivery network (cdn).