Misplaced Pages

#51948

51-556: Interior Gateway Routing Protocol ( IGRP ) is a distance vector interior gateway protocol (IGP) developed by Cisco . It is used by routers to exchange routing data within an autonomous system . IGRP is a proprietary protocol . IGRP was created in part to overcome the limitations of RIP (maximum hop count of only 15, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including bandwidth , delay , load , and reliability ; to compare two routes these metrics are combined into

102-415: A CPU . More sophisticated devices use application-specific integrated circuits (ASICs) to increase performance or add advanced filtering and firewall functionality. When multiple routers are used in interconnected networks, the routers can exchange information about destination addresses using a routing protocol . Each router builds up a routing table , a list of routes, between two computer systems on

153-415: A Transmission Control Protocol (TCP) session. Routers with BGP implementation determine the shortest path across a network based on a range of factors other than hops. BGP can also be configured by administrators so that certain routes are preferred or avoided. BGP is used by internet service providers (ISPs) and telecommunication companies. Among the distance-vector protocols that have been described as

204-478: A classful routing protocol. Because the protocol has no field for a subnet mask , the router assumes that all subnetwork addresses within the same Class A, Class B, or Class C network have the same subnet mask as the subnet mask configured for the interfaces in question. This contrasts with classless routing protocols that can use variable length subnet masks . Classful protocols have become less popular as they are wasteful of IP address space . In order to address

255-680: A switching node using software and an interface computer were first proposed by Donald Davies for the NPL network in 1966. The same idea was conceived by Wesley Clark the following year for use in the ARPANET , which were named Interface Message Processors (IMPs). The first interface computer was implemented at the National Physical Laboratory in the United Kingdom in early 1969, followed later that year by

306-497: A wide area network (WAN), so they may have considerable memory installed, multiple WAN interface connections, and substantial onboard data processing routines. They may also provide connectivity to groups of file servers or other external networks. In enterprises, a core router may provide a collapsed backbone interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth but lack some of

357-511: A DV from B that tells A there is a path via B to D, with a distance (or cost) of 7. Since the current "shortest-path" to B is 3, then A knows it has a path to D that costs 7+3=10. This path to D of length 10 (via B) is shorter than the existing "shortest-path" to D of length 28 (via C), so it becomes the new "shortest-path" to D. Router (computing) A router is a computer and networking device that forwards data packets between computer networks , including internetworks such as

408-424: A hybrid, because it uses routing methods associated with link-state routing protocols , is the proprietary Enhanced Interior Gateway Routing Protocol (EIGRP). It was developed by Cisco in the 1980s and was designed to offer better convergence and cause less network traffic between routers than the link-state routing protocol Open Shortest Path First (OSPF). Another example of a distance-vector routing protocol

459-421: A number of loop-free distance vector protocols have been developed — notable examples are EIGRP , DSDV and Babel . These avoid loop formation in all cases, but suffer from increased complexity, and their deployment has been slowed down by the success of link state routing protocols such as OSPF . In this network we have 4 routers A, B, C and D: [REDACTED] We mark the current time (or iteration) in

510-414: A security feature by all experts. Some experts argue that open source routers are more secure and reliable than closed source routers because errors and potentially exploitable vulnerabilities are more likely to be discovered and addressed in an open-source environment. Routers are also often distinguished on the basis of the network in which they operate. A router in a local area network (LAN) of

561-463: A single metric, using a formula which can be adjusted through the use of pre-set constants. By default, the IGRP composite metric is a sum of the segment delays and the lowest segment bandwidth. The maximum configurable hop count of IGRP-routed packets is 255 (default 100), and routing updates are broadcast every 90 seconds (by default). IGRP uses protocol number 9 for communication. IGRP is considered

SECTION 10

#1732801673052

612-632: A single organization is called an interior router . A router that is operated in the Internet backbone is described as exterior router . While a router that connects a LAN with the Internet or a wide area network (WAN) is called a border router , or gateway router . Routers intended for ISP and major enterprise connectivity usually exchange routing information using the Border Gateway Protocol (BGP). RFC   4098 defines

663-418: A variety of sources, such as a default or static routes that are configured manually, or dynamic entries from routing protocols where the router learns routes from other routers. A default route is one that is used to route all traffic whose destination does not otherwise appear in the routing table; it is common – even necessary – in small networks, such as a home or small business where

714-444: Is Babel . The Bellman–Ford algorithm does not prevent routing loops from happening and suffers from the count to infinity problem . The core of the count-to-infinity problem is that if A tells B that it has a path somewhere, there is no way for B to know if the path has B as a part of it. To see the problem, imagine a subnet connected like A–B–C–D–E–F, and let the metric between the routers be "number of jumps". Now suppose that A

765-491: Is completely unsupported. In the new Cisco CCNA curriculum (version 4), IGRP is mentioned only briefly, as an "obsolete protocol". Distance vector Distance-vector routing protocols use the Bellman–Ford algorithm to calculate the best route. Another way of calculating the best route across a network is based on link cost, and is implemented through link-state routing protocols . The term distance vector refers to

816-738: Is in common use. Some routers can connect to Data service units for T1 connections via serial ports. The hierarchical internetworking model divides enterprise networks into three layers: core, distribution, and access. Access routers, including small office/home office (SOHO) models, are located at home and customer sites such as branch offices that do not need hierarchical routing of their own. Typically, they are optimized for low cost. Some SOHO routers are capable of running alternative free Linux-based firmware like Tomato , OpenWrt , or DD-WRT . Distribution routers aggregate traffic from multiple access routers. Distribution routers are often responsible for enforcing quality of service across

867-404: Is sent to all its neighbours that are configured to use the same distance-vector routing protocol. Once a router has this information it is able to amend its own routing table to reflect the changes and then inform its neighbours of the changes. This process has been described as ‘routing by rumour’ because routers are relying on the information they receive from other routers and cannot determine if

918-411: Is taken offline. In the vector-update-process B notices that the route to A, which was distance 1, is down – B does not receive the vector update from A. The problem is, B also gets an update from C, and C is still not aware of the fact that A is down – so it tells B that A is only two jumps from C (C to B to A). Since B doesn't know that the path from C to A is through itself (B), it updates its table with

969-413: Is the simplest and most easily implemented: the router simply drops new incoming packets once buffer space in the router is exhausted. RED probabilistically drops datagrams early when the queue exceeds a pre-configured portion of the buffer, until reaching a pre-determined maximum, when it drops all incoming packets, thus reverting to tail drop. WRED can be configured to drop packets more readily dependent on

1020-482: Is used to enable data packets to be forwarded from one transmission system to another. Routers may also be used to connect two or more logical groups of computer devices known as subnets , each with a unique network prefix . Routers may provide connectivity within enterprises, between enterprises and the Internet, or between internet service providers ' (ISPs') networks, they are also responsible for directing data between different networks. The largest routers (such as

1071-652: The Cisco CRS-1 or Juniper PTX) interconnect the various ISPs, or may be used in large enterprise networks. Smaller routers usually provide connectivity for typical home and office networks. All sizes of routers may be found inside enterprises. The most powerful routers are usually found in ISPs, academic and research facilities. Large businesses may also need more powerful routers to cope with ever-increasing demands of intranet data traffic. A hierarchical internetworking model for interconnecting routers in large networks

SECTION 20

#1732801673052

1122-520: The International Network Working Group (INWG). These gateway devices were different from most previous packet switching schemes in two ways. First, they connected dissimilar kinds of networks, such as serial lines and local area networks . Second, they were connectionless devices, which had no role in assuring that traffic was delivered reliably, leaving that function entirely to the hosts . This particular idea,

1173-637: The end-to-end principle , was pioneered in the CYCLADES network. The idea was explored in more detail, with the intention to produce a prototype system as part of two contemporaneous programs. One was a program at Xerox PARC to explore new networking technologies, which produced the PARC Universal Packet system. Some time after early 1974, the first Xerox routers became operational. Due to corporate intellectual property concerns, it received little attention outside Xerox for years. The other

1224-796: The IMPs at the University of California, Los Angeles , the Stanford Research Institute , the University of California, Santa Barbara , and the University of Utah School of Computing in the United States. All were built with the Honeywell 516 . These computers had fundamentally the same functionality as a router does today. The idea for a router (called a gateway at the time) initially came about through an international group of computer networking researchers called

1275-430: The algorithm with T, and begin (at time 0, or T=0) by creating distance matrices for each router to its immediate neighbours. As we build the routing tables below, the shortest path is highlighted in green, and a new shortest path is highlighted in yellow. Grey columns indicate nodes that are not neighbors of the current node, and are therefore not considered as a valid direction in its table. Red indicates invalid entries in

1326-432: The best route, routers regularly exchange information with neighbouring routers, usually their routing table , hop count for a destination network and possibly other traffic related information. Routers that implement distance-vector protocol rely purely on the information provided to them by other routers, and do not assess the network topology . Distance-vector protocols update the routing tables of routers and determine

1377-405: The chance of forming loops and uses a maximum number of hops to counter the 'count to infinity' problem. These measures avoid the formation of routing loops in some, but not all, cases. The addition of a hold time (refusing route updates for a few minutes after a route retraction) avoids loop formation in virtually all cases, but causes a significant increase in convergence times. More recently,

1428-508: The default route simply sends all non-local traffic to the Internet service provider . The default route can be manually configured (as a static route); learned by dynamic routing protocols; or be obtained by DHCP . A router can run more than one routing protocol at a time, particularly if it serves as an autonomous system border router between parts of a network that run different routing protocols; if it does so, then redistribution may be used (usually selectively) to share information between

1479-402: The different protocols running on the same router. Besides deciding to which interface a packet is forwarded, which is handled primarily via the routing table, a router also has to manage congestion when packets arrive at a rate higher than the router can process. Three policies commonly used are tail drop , random early detection (RED), and weighted random early detection (WRED). Tail drop

1530-502: The fact that the protocol manipulates vectors ( arrays ) of distances to other nodes in the network. The distance vector algorithm was the original ARPANET routing algorithm and was implemented more widely in local area networks with the Routing Information Protocol (RIP). Distance-vector routing protocols use the Bellman–Ford algorithm . In these protocols, each router does not possess information about

1581-416: The features of edge routers. External networks must be carefully considered as part of the overall security strategy of the local network. A router may include a firewall , VPN handling, and other security functions, or they may be handled by separate devices. Routers also commonly perform network address translation which restricts connections initiated from external connections but is not recognized as

Interior Gateway Routing Protocol - Misplaced Pages Continue

1632-424: The full network topology . It advertises its distance value (DV) calculated to other routers and receives similar advertisements from other routers unless changes are done in the local network or by neighbours (routers). Using these routing advertisements each router populates its routing table. In the next advertisement cycle, a router advertises updated information from its routing table. This process continues until

1683-613: The global Internet . A router is connected to two or more data lines from different IP networks . When a data packet comes in on a line, the router reads the network address information in the packet header to determine the ultimate destination. Then, using information in its routing table or routing policy , it directs the packet to the next network on its journey. Data packets are forwarded from one router to another through an internetwork until it reaches its destination node . The most familiar type of IP routers are home and small office routers that forward IP packets between

1734-414: The home computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks to powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone . Routers can be built from standard computer parts but are mostly specialized purpose-built computers . Early routers used software -based forwarding, running on

1785-435: The hops, that is numbers of routers that need to be passed to reach the destination network. RIP is an interior gateway protocol , so it can be used in local area networks (LANs) on interior or border routers. Routers with RIPv1 implementation exchange their routing tables with neighbouring routers by broadcasting a RIPv1 packet every 30 second into all connected networks. RIPv1 is not suitable for large networks as it limits

1836-402: The information is actually valid and true. There are a number of features which can be used to help with instability and inaccurate routing information. The oldest routing protocol , and the oldest distance-vector protocol, is version 1 of the Routing Information Protocol (RIPv1). RIPv1 was formally standardised in 1988. It establishes the shortest path across a network purely on the basis of

1887-401: The interconnected networks. The software that runs the router is composed of two functional processing units that operate simultaneously, called planes : A router may have interfaces for multiple types of physical layer connections, such as copper cables, fiber optic , or wireless transmission. It can also support multiple network layer transmission standards. Each network interface

1938-492: The issues of address space and other factors, Cisco created EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP adds support for VLSM (variable length subnet mask) and adds the Diffusing Update Algorithm (DUAL) in order to improve routing and provide a loopless environment. EIGRP has completely replaced IGRP, making IGRP an obsolete routing protocol. In Cisco IOS versions 12.3 and greater, IGRP

1989-423: The layer-3 IP packet, specifically the destination IP address. When a router receives a packet, it searches its routing table to find the best match between the destination IP address of the packet and one of the addresses in the routing table. 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

2040-505: The mid-1970s and in the 1980s, general-purpose minicomputers served as routers. Modern high-speed routers are network processors or highly specialized computers with extra hardware acceleration added to speed both common routing functions, such as packet forwarding, and specialized functions such as IPsec encryption. There is substantial use of Linux and Unix software-based machines, running open source routing code, for research and other applications. The Cisco IOS operating system

2091-433: The new value "B to A = 2 + 1". Later on, B forwards the update to C and due to the fact that A is reachable through B (From C's point of view), C decides to update its table to "C to A = 3 + 1". This slowly propagates through the network until it becomes infinity (in which case the algorithm corrects itself, due to the relaxation property of Bellman-Ford). RIP uses the split horizon with poison reverse technique to reduce

Interior Gateway Routing Protocol - Misplaced Pages Continue

2142-456: The number of hops to 15. This hop limit was introduced to avoid routing loops, but also means that networks that are connected through more than 15 routers are unreachable. The distance-vector protocol designed for use in wide area networks (WANs) is the Border Gateway Protocol (BGP). BGP is an exterior gateway protocol and therefore implemented on border and exterior routers on the Internet . It exchanges information between routers through

2193-471: The packet payload, 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). For pure IP forwarding, a router is designed to minimize the state information associated with individual packets. Once a packet is forwarded, the router does not retain any historical information about the packet. The routing table itself can contain information derived from

2244-460: The route on which a packet will be sent by the next hop which is the exit interface of the router and the IP address of the interface of the receiving router. Distance is a measure of the cost to reach a certain node. The least cost route between any two nodes is the route with minimum distance. Updates are performed periodically in a distance-vector protocol where all or part of a router's routing table

2295-585: The routing tables of each router converge to stable values. Some of these protocols have the disadvantage of slow convergence. Examples of distance-vector routing protocols: Routers that use distance-vector protocol determine the distance between themselves and a destination. The best route for data through a data network is measured in terms of the numbers of routers (hops) a packet has to pass through to reach its destination network. Additionally, some distance-vector protocols take into account other traffic information, such as network latency . To establish

2346-457: The table since they refer to distances from a node to itself, or via itself. For example: A receives a DV from C that tells A there is a path via C to D, with a distance (or cost) of 5. Since the current "shortest-path" to C is 23, then A knows it has a path to D that costs 23+5=28. As there are no other shorter paths that A knows about, it puts this as its current estimate for the shortest-path from itself (A) to D, via C. For instance: A receives

2397-411: The type of traffic. Another function a router performs is traffic classification and deciding which packet should be processed first. This is managed through QoS , which is critical when Voice over IP is deployed, so as not to introduce excessive latency . Yet another function a router performs is called policy-based routing where special rules are constructed to override the rules derived from

2448-440: The types of BGP routers according to their functions: Wi-Fi routers combine the functions of a router with those of a wireless access point . They are typically devices with a small form factor, operating on the standard electric power supply for residential use. Connected to the Internet as offered by an Internet service provider , they provide Internet access through a wireless network for home or office use. The concepts of

2499-408: Was independently designed. Major router operating systems, such as Junos and NX-OS , are extensively modified versions of Unix software. The main purpose of a router is to connect multiple networks and forward packets destined either for directly attached networks or more remote networks. A router is considered a layer-3 device because its primary forwarding decision is based on the information in

2550-436: Was led by William Yeager and MIT's by Noel Chiappa . Virtually all networking now uses TCP/IP, but multiprotocol routers are still manufactured. They were important in the early stages of the growth of computer networking when protocols other than TCP/IP were in use. Modern routers that handle both IPv4 and IPv6 are multiprotocol but are simpler devices than ones processing AppleTalk, DECnet, IPX, and Xerox protocols. From

2601-782: Was the DARPA -initiated program, which created the TCP/IP architecture in use today. The first true IP router was developed by Ginny Travers at BBN , as part of that DARPA-initiated effort, during 1975–1976. By the end of 1976, three PDP-11 -based routers were in service in the experimental prototype Internet. Mike Brecia, Ginny Travers, and Bob Hinden received the IEEE Internet Award for early IP routers in 2008. The first multiprotocol routers were independently created by staff researchers at MIT and Stanford in 1981 and both were also based on PDP-11s. Stanford's router program

SECTION 50

#1732801673052
#51948