From Wikipedia, the free encyclopedia LAN switching
LAN switching
This article addresses packet switching in computer 80/20 rule: users spend 80 percent of their time on their
networks. local segment.
Bridged networks break up collision domains, but the
LAN switching is a form of packet switching used in local network remains one large broadcast domain. Similarly,
area networks. Switching technologies are crucial to net- layer 2 switches (bridges) cannot break up broadcast do-
work design, as they allow traffic to be sent only where mains, which can cause performance issues and limits
it is needed in most cases, using fast, hardware-based the size of your network. Broadcast and multicasts, along
methods. with the slow convergence of spanning tree, can cause
major problems as the network grows. Because of these
Layer 2 switching problems, layer 2 switches cannot completely replace
routers in the internetwork.
Layer 2 switching is hardware based,[1] which means it
uses the media access control address (MAC address)
from the host’s network interface cards (NICs) to decide Layer 3 switching
where to forward frames. Switches use application-spe- The only difference between a layer 3 switch and router
cific integrated circuit (ASICs) to build and maintain fil- is the way the administrator creates the physical imple-
ter tables (also known as MAC address tables). One way to mentation. Also, traditional routers use microprocessors
think of a layer 2 switch is as a multiport bridge. to make forwarding decisions, and the switch performs
Layer 2 switching provides the following only hardware-based packet switching. However, some
• Hardware-based bridging (MAC) traditional routers can have other hardware functions as
• Wire speed well in some of the higher-end models. Layer 3 switch-
• High speed es can be placed anywhere in the network because they
• Low latency handle high-performance LAN traffic and can cost-effec-
• Low cost tively replace routers. Layer 3 switching is all hardware-
Layer 2 switching is highly efficient because there is no based packet forwarding, and all packet forwarding is
modification to the data packet, only to the frame encap- handled by hardware ASICs. Layer 3 switches really are
sulation of the packet, and only when the data packet is no different functionally than a traditional router and
passing through dissimilar media (such as from Ethernet perform the same functions, which are listed here
to FDDI). Layer 2 switching is used for workgroup con- • Determine paths based on logical addressing
nectivity and network segmentation (breaking up colli- • Run layer 3 checksums (on header only)
sion domains). This allows a flatter network design with • Use Time to Live (TTL)
more network segments than traditional 10BaseT shared • Process and respond to any option information
networks. Layer 2 switching has helped develop new • Update Simple Network Management Protocol
components in the network infrastructure (SNMP) managers with Management Information
• Server farms — Servers are no longer distributed to Base (MIB) information
physical locations because virtual LANs can be • Provide Security
created to create broadcast domains in a switched The benefits of layer 3 switching include the following
internetwork. This means that all servers can be • Hardware-based packet forwarding
placed in a central location, yet a certain server can • High-performance packet switching
still be part of a workgroup in a remote branch, for • High-speed scalability
example. • Low latency
• Intranets — Allows organization-wide client/server • Lower per-port cost
communications based on a Web technology. • Flow accounting
These new technologies allow more data to flow off from • Security
local subnets and onto a routed network, where a • Quality of service (QoS)
router’s performance can become the bottleneck. 1. SWITCHING:
Switching algorithm is relatively simple. it is the same for
Limitations most of the routing protocols. in most cases a host deter-
Layer 2 switches have the same limitations as bridge net- mines that it must send a packet to another host. Hav-
works. Bridges are good if a network is designed by the ing acquired a routers address by some means, the source
1
From Wikipedia, the free encyclopedia LAN switching
host send a packet address specifically to a routers phys- For example, a number of users can be defined as
ical(MAC_) address, this time with the protocol(network a Video group and be assigned more priority, or band-
layer)address of the destination host. width, based on the need for video conferencing.
As it examines the packet’s destination protocol ad-
dress, the router determines that it either knows or does
not know how to forward packet to the next hop. If the
Multi-layer switching (MLS)
router does not know how to do it, it typically drops the Main article: Multilayer switch
packet. if it knows how to forward packet, however, it Multi-layer switching combines layer 2, 3, and 4 switch-
changes the destinations physical address to that of the ing technologies and provides high-speed scalability with
next hop and transmits the packet. low latency. It accomplishes this high combination of
The next hop may be the destination or the next high-speed scalability with low latency by using huge fil-
router, which executes the same switching process. As ter tables based on the criteria designed by the network
the packet moves through the internetwork, its physical administrator.
address changes, but its protocol address remains same. Multi-layer switching can move traffic at wire speed
IEEE has developed the hierarchical terminology that and also provide layer 3 routing, which can remove the
is useful in describing this process. The network devices bottleneck from the network routers. This technology is
without capability to forward packets between subnet- based on the idea of "route once, switch many".
works are called end system(ES), whereas network de- Multi-layer switching can make routing/switching
vices with this capabilities are called intermediate sys- decisions based on the following
tems(IS). IS are further divided into those that can com- • MAC source/destination address in a Data Link frame
municate within routing domain(Intradomain ES) and • IP source/destination address in the Network layer
those that communicate both within and between rout- header
ing domains(Interdomains IS) a routing domain is gener- • Protocol field in the Network layer header
ally considered as portion of an internetwork under com- • Port source/destination numbers in the Transport
mon administrative authority that is regulated by a par- layer header
ticular set of administrative guidlines. Routing domains There is no performance difference between a layer 3
are also called as autonomous systems. and a layer 4 switch because the routing/switching is all
hardware based.
Layer 4 switching
Layer 4 switching is considered a hardware-based layer 3
See also
switching technology that can also consider the applica- • Network switch
tion used (for example, Telnet or FTP). • Content switch
Layer 4 switching provides additional routing above • Residential gateway
layer 3 by using the port numbers found in the Transport
layer header to make routing decisions.
These port numbers are found in Request for Com-
References
ments (RFC) 1700 and reference the upper-layer protocol, [1] Techsoft Computing
program, or application.
Layer 4 information has been used to help make rout- External links
ing decisions for quite a while. For example, extended ac-
cess lists can filter packets based on layer 4 port num- • Arista Networks industries leading 10G data center
bers. Another example is accounting information gath- switching products
ered by open standards using sFlow provided by com- • Cisco IT Case Studies about routing and switching
panies like Arista Networks or proprietary solutions like • Is Switching a Commodity?" Fact or Fiction with
NetFlow switching in Cisco’s higher-end routers. Jennifer Geisler (Flash software required)
The largest benefit of layer 4 switching is that the
network administrator can configure a layer 4 switch to
prioritize data traffic by application, which means a QoS
can be defined for each user.
Retrieved from "http://en.wikipedia.org/w/index.php?title=LAN_switching&oldid=470417323"
Categories:
• Telecommunications equipment
• Local area networks
2
From Wikipedia, the free encyclopedia LAN switching
This page was last modified on 9 January 2012 at 11:27. Text is available under the Creative Commons Attribution-
ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of
the Wikimedia Foundation, Inc., a non-profit organization.Contact us
Privacy policy About Wikipedia Disclaimers
3