Router (computing)
More sophisticated devices use application-specific integrated circuits (ASICs) to increase performance or add advanced filtering and firewall functionality.
Routers may also be used to connect two or more logical groups of computer devices known as subnets, each with a unique network prefix.
[9] The largest routers (such as the Cisco CRS-1 or Juniper PTX) interconnect the various ISPs, or may be used in large enterprise networks.
Large businesses may also need more powerful routers to cope with ever-increasing demands of intranet data traffic.
[16][17] The hierarchical internetworking model divides enterprise networks into three layers: core, distribution, and access.
Some SOHO routers are capable of running alternative free Linux-based firmware like Tomato, OpenWrt, or DD-WRT.
[24] Routers intended for ISP and major enterprise connectivity usually exchange routing information using the Border Gateway Protocol (BGP).
They are typically devices with a small form factor, operating on the standard electric power supply for residential use.
The concepts of a switching node using software and an interface computer were first proposed by Donald Davies for the NPL network in 1966.
[31][32][33] The same idea was conceived by Wesley Clark the following year for use in the ARPANET, which were named Interface Message Processors (IMPs).
Second, they were connectionless devices, which had no role in assuring that traffic was delivered reliably, leaving that function entirely to the hosts.
[41] The idea was explored in more detail, with the intention to produce a prototype system as part of two contemporaneous programs.
[46] Mike Brecia, Ginny Travers, and Bob Hinden received the IEEE Internet Award for early IP routers in 2008.
Modern routers that handle both IPv4 and IPv6 are multiprotocol but are simpler devices than ones processing AppleTalk, DECnet, IPX, and Xerox protocols.
There is substantial use of Linux and Unix software-based machines, running open source routing code, for research and other applications.
Major router operating systems, such as Junos and NX-OS, are extensively modified versions of Unix software.
Once a match is found, the packet is encapsulated in the layer-2 data link frame for the outgoing interface indicated in the table entry.
A router typically does not look into the packet payload,[52] but only at the layer-3 addresses to make a forwarding decision, plus optionally other information in the header for hints on, for example, quality of service (QoS).
[57] Some of the functions may be performed through an application-specific integrated circuit (ASIC) to avoid the overhead of scheduling CPU time to process the packets.
