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77-485: EIGRP is used on a router to share routes with other routers within the same autonomous system . Unlike other well known routing protocols, such as RIP , EIGRP only sends incremental updates , reducing the workload on the router and the amount of data that needs to be transmitted. EIGRP replaced the Interior Gateway Routing Protocol (IGRP) in 1993. One of the major reasons for this was

154-667: A data section (the payload data for the application). The UDP datagram header consists of 4 fields, each of which is 2 bytes (16 bits): The use of the Checksum and Source Port fields is optional in IPv4 (light purple background in table). In IPv6 only the Source Port field is optional. If not used, these fields should be set to zero. The method used to compute the checksum is defined in RFC ; 768 , and efficient calculation

231-572: A port number to identify traffic. Rather, EIGRP is designed to work on top of Layer 3 (i.e. the IP protocol). Since EIGRP does not use TCP for communication, it implements Cisco's Reliable Transport Protocol (RTP) to ensure that EIGRP router updates are delivered to all neighbors completely. The Reliable Transport Protocol also contains other mechanisms to maximize efficiency and support multicasting . EIGRP uses 224.0.0.10 as its multicast address and protocol number 88. Cisco Systems now classifies EIGRP as

308-680: 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

385-497: 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

462-500: A carry-out (17th bit) is produced, swing that 17th carry bit around and add it to the least significant bit of the running total. Finally, the sum is then ones' complemented to yield the value of the UDP checksum field. If the checksum calculation results in the value zero (all 16 bits 0) it should be sent as the ones' complement (all 1s) as a zero-value checksum indicates no checksum has been calculated. In this case, any specific processing

539-411: A combination of TCP and TLS to ensure reliability and security respectively. This means that HTTP/3 uses a single handshake to set up a connection, rather than having two separate handshakes for TCP and TLS, meaning the overall time to establish a connection is reduced. Transmission Control Protocol is a connection-oriented protocol and requires handshaking to set up end-to-end communications. Once

616-450: A connection and that UDP doesn't keep track of what it has sent. UDP provides checksums for data integrity , and port numbers for addressing different functions at the source and destination of the datagram. It has no handshaking dialogues and thus exposes the user's program to any unreliability of the underlying network; there is no guarantee of delivery, ordering, or duplicate protection. If error-correction facilities are needed at

693-432: A different header layout, the method used to compute the checksum is changed accordingly: Any transport or other upper-layer protocol that includes the addresses from the IP header in its checksum computation must be modified for use over IPv6, to include the 128-bit IPv6 addresses instead of 32-bit IPv4 addresses. When computing the checksum, again a pseudo header is used that mimics the real IPv6 header : The checksum

770-569: A distance vector routing protocol, but it is normally said to be a hybrid routing protocol. While EIGRP is an advanced routing protocol that combines many of the features of both link-state and distance-vector routing protocols, EIGRP's DUAL algorithm contains many features which make it more of a distance vector routing protocol than a link-state routing protocol. Despite this, EIGRP contains many differences from most other distance-vector routing protocols, including: EIGRP associates six different vector metrics with each route and considers only four of

847-468: A feasible successor with the lowest total distance (the distance as reported by the feasible successor plus the cost of the link to this neighbor) to a new successor and the destination will remain in the passive state. The feasibility condition is a sufficient condition for loop freedom in EIGRP-routed network. It is used to select the successors and feasible successors that are guaranteed to be on

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924-540: A high degree of reliability, a protocol such as the Transmission Control Protocol may be used instead. Most often, UDP applications do not employ reliability mechanisms and may even be hindered by them. Streaming media , real-time multiplayer games and voice over IP (VoIP) are examples of applications that often use UDP. In these particular applications, loss of packets is not usually a fatal problem. In VoIP, for example, latency and jitter are

1001-455: A loop-free route to a destination. Its simplified formulation is strikingly simple: or in other words, It is important to realize that this condition is a sufficient, not a necessary, condition. That means that neighbors which satisfy this condition are guaranteed to be on a loop-free path to some destination, however, there may be also other neighbors on a loop-free path which do not satisfy this condition. However, such neighbors do not provide

1078-465: A relationship, known as an adjacency . The entire routing table is exchanged between both routers at this time. After the exchange has completed, only differential changes are sent. EIGRP is often considered a hybrid protocol because it also sends link state updates when link states change. EIGRP supports the following features: Example of setting up EIGRP on a Cisco IOS router for a private network . The 0.0.15.255 wildcard in this example indicates

1155-480: A router from another router within the same autonomous system, has a default administrative distance of 90. EIGRP routing information, that has come from an EIGRP-enabled router outside the autonomous system, has a default administrative distance of 170. EIGRP does not operate using the Transmission Control Protocol (TCP) or the User Datagram Protocol (UDP). This means that EIGRP does not use

1232-414: 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

1309-632: 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

1386-724: A socket to its endpoint of data transmission, which is a combination of an IP address and a port . In this way, UDP provides application multiplexing . A port is a software structure that is identified by the port number , a 16-bit integer value, allowing for port numbers between 0 and 65535. Port 0 is reserved but is a permissible source port value if the sending process does not expect messages in response. The Internet Assigned Numbers Authority (IANA) has divided port numbers into three ranges. Port numbers 0 through 1023 are used for common, well-known services. On Unix -like operating systems , using one of these ports requires superuser operating permission. Port numbers 1024 through 49151 are

1463-443: A subnetwork with a maximum of 4094 hosts—it is the bitwise complement of the subnet mask 255.255.240.0. The no auto-summary command prevents automatic route summarization on classful boundaries, which would otherwise result in routing loops in discontiguous networks. EIGRP is a distance vector & Link State routing protocol that uses the diffusing update algorithm (DUAL) (based on work from SRI International ) to improve

1540-418: 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

1617-411: A working route to the same destination, although with a higher distance. At any time, a router can send a packet to a destination marked "Passive" through any of its successors or feasible successors without alerting them in the first place, and this packet will be delivered properly. Feasible successors are also recorded in the topology table. The feasible successor effectively provides a backup route in

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1694-468: Is a computer and networking device that forwards data packets between computer networks , including internetworks such as 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

1771-431: Is computed over the following fields: Lacking reliability, UDP applications may encounter some packet loss, reordering, errors or duplication. If using UDP, the end-user applications must provide any necessary handshaking such as real-time confirmation that the message has been received. Applications, such as TFTP , may add rudimentary reliability mechanisms into the application layer as needed. If an application requires

1848-403: Is discussed in RFC  1071 : Checksum is the 16-bit ones' complement of the ones' complement sum of a pseudo header of information from the IP header, the UDP header, and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets. In other words, all 16-bit words are summed using ones' complement arithmetic. Add the 16-bit values up. On each addition, if

1925-414: Is generally transmitted using UDP. Real-time video and audio streaming protocols are designed to handle occasional lost packets, so only slight degradation in quality occurs, rather than large delays if lost packets were retransmitted. Because both TCP and UDP run over the same network, in the mid-2000s a few businesses found that an increase in UDP traffic from these real-time applications slightly hindered

2002-738: 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

2079-423: Is limited to four. This limit can be changed in the range from 1 to 6. In more recent versions of Cisco IOS (e.g. 12.4), this range is between 1 and 16. A destination in the topology table can be marked either as passive or active . A passive state is a state when the router has identified the successor(s) for the destination. The destination changes to active state when the current successor no longer satisfies

2156-463: Is not required at the receiver, because all 0s and all 1s are equal to zero in 1's complement arithmetic. The differences between IPv4 and IPv6 are in the pseudo header used to compute the checksum, and that the checksum is not optional in IPv6. Under specific conditions, a UDP application using IPv6 is allowed to use a zero UDP zero-checksum mode with a tunnel protocol. When UDP runs over IPv4,

2233-489: Is preferable to waiting for packets delayed due to retransmission , which may not be an option in a real-time system . The protocol was designed by David P. Reed in 1980 and formally defined in RFC   768 . UDP is a simple message-oriented transport layer protocol that is documented in RFC  768 . Although UDP provides integrity verification (via checksum ) of the header and payload, it provides no guarantees to

2310-510: Is set to 1 by default, which means load balancing on equal cost paths. The maximum variance is 128. The minimum metric of a route is multiplied by the variance value. Each path with a metric that is smaller than the result is used in load balancing. With the functionality of the Unequal Path Cost Load Balancing on EIGRP, OSPF protocol is unable to design the network by Unequal Path Cost Load Balancing. Regarding

2387-462: Is that if K 5 {\displaystyle K_{5}} is set to zero, the term K 5 K 4 + Reliability {\displaystyle {\tfrac {K_{5}}{K_{4}+{\text{Reliability}}}}} is not used (i.e. taken as 1) . The default is for K 1 {\displaystyle K_{1}} and K 3 {\displaystyle K_{3}} to be set to 1, and

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2464-413: 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

2541-482: 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

2618-497: Is verified by testing the feasibility condition . Thus, every successor is also a feasible successor. However, in most references about EIGRP the term feasible successor is used to denote only those routes which provide a loop-free path but which are not successors (i.e. they do not provide the least distance). From this point of view, for a reachable destination, there is always at least one successor, however, there might not be any feasible successors. A feasible successor provides

2695-652: 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

2772-520: 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,

2849-434: The User Datagram Protocol ( UDP ) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets ) to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP does not require prior communication to set up communication channels or data paths. UDP is a connectionless protocol meaning that messages are sent without negotiating

2926-637: 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

3003-419: The feasibility condition and there are no feasible successors identified for that destination (i.e. no backup routes are available). The destination changes back from active to passive when the router received replies to all queries it has sent to its neighbors. Notice that if a successor stops satisfying the feasibility condition but there is at least one feasible successor available, the router will promote

3080-449: 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 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,

3157-402: The registered ports used for IANA-registered services. Ports 49152 through 65535 are dynamic ports that are not officially designated for any specific service and may be used for any purpose. These may also be used as ephemeral ports , which software running on the host may use to dynamically create communications endpoints as needed. A UDP datagram consists of a datagram header followed by

Enhanced Interior Gateway Routing Protocol - Misplaced Pages Continue

3234-471: The upper layer protocol for message delivery and the UDP layer retains no state of UDP messages once sent. For this reason, UDP sometimes is referred to as Unreliable Datagram Protocol . If transmission reliability is desired, it must be implemented in the user's application. A number of UDP's attributes make it especially suited for certain applications. Applications can use datagram sockets to establish host-to-host communications. An application binds

3311-796: 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

3388-439: The K values as needed to consider the other Vector metrics. For the purposes of comparing routes, these are combined together in a weighted formula to produce a single overall metric: where the various constants ( K 1 {\displaystyle K_{1}} through K 5 {\displaystyle K_{5}} ) can be set by the user to produce varying behaviors. An important and unintuitive fact

3465-402: The Unequal Path Cost Load Balancing function on industry usage, the network design can be flexible with the traffic management. Cisco released details of the proprietary EIGRP routing protocol in an RFC in an effort to assist companies whose networks operate in a multi-vendor environment. The protocol is described in RFC   7868 . EIGRP was developed 20 years ago, yet it is still one of

3542-400: The case that existing successors become unavailable. Also, when performing unequal-cost load-balancing (balancing the network traffic in inverse proportion to the cost of the routes), the feasible successors are used as next hops in the routing table for the load-balanced destination. By default, the total count of successors and feasible successors for a destination stored in the routing table

3619-475: The change to classless IPv4 addresses in the Internet Protocol , which IGRP could not support. Almost all routers contain a routing table that contains rules by which traffic is forwarded in a network. If the router does not contain a valid path to the destination, the traffic is discarded. EIGRP is a dynamic routing protocol by which routers automatically share route information. This eases

3696-445: The checksum is computed using a pseudo header that contains some of the same information from the real IPv4 header . The pseudo header is not the real IPv4 header used to send an IP packet, it is used only for the checksum calculation. UDP checksum computation is optional for IPv4. If a checksum is not used it should be set to the value zero. The checksum is calculated over the following fields: As IPv6 has larger addresses and

3773-508: 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

3850-402: 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

3927-409: The efficiency of the protocol and to help prevent calculation errors when attempting to determine the best path to a remote network . EIGRP determines the value of the path using five metrics: bandwidth, load, delay, reliability and MTU. EIGRP uses five different messages to communicate with its neighbor routers – Hello, Update, Query, Reply, and Acknowledgement. EIGRP routing information, exchanged to

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4004-430: The factor of 256 (effectively bit-shifting it 8 bits to the left), the value is extended into 32 bits, and vice versa. This way, redistributing information between EIGRP and IGRP involves simply dividing or multiplying the metric value by a factor of 256, which is done automatically. A feasible successor for a particular destination is a next hop router that is guaranteed not to be a part of a routing loop . This condition

4081-416: 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

4158-404: The interface Bandwidth and Delay configuration values with following calculations: On Cisco routers, the interface bandwidth is a configurable static parameter expressed in kilobits per second (setting this only affects metric calculation and not actual line bandwidth). Dividing a value of 10 kbit/s (i.e. 10 Gbit/s) by the interface bandwidth statement value yields a result that is used in

4235-423: 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

4312-505: 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

4389-447: The network interface level, an application may instead use Transmission Control Protocol (TCP) or Stream Control Transmission Protocol (SCTP) which are designed for this purpose. UDP is suitable for purposes where error checking and correction are either not necessary or are performed in the application; UDP avoids the overhead of such processing in the protocol stack . Time-sensitive applications often use UDP because dropping packets

4466-471: 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

4543-475: 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 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

4620-407: The path will become unavailable. EIGRP is designed to detect these changes and will attempt to find a new path to the destination. The old path that is no longer available is removed from the routing table. Unlike most distance vector routing protocols, EIGRP does not transmit all the data in the router's routing table when a change is made, but will only transmit the changes that have been made since

4697-496: The performance of applications using TCP such as point of sale , accounting , and database systems (when TCP detects packet loss, it will throttle back its data rate usage). Some VPN systems such as OpenVPN may use UDP and perform error checking at the application level while implementing reliable connections. QUIC is a transport protocol built on top of UDP. QUIC provides a reliable and secure connection. HTTP/3 uses QUIC as opposed to earlier versions of HTTPS which use

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4774-693: The primary Cisco routing protocols due to its purported usability and scalability in comparison to other protocols . Cisco has stated that EIGRP is an open standard but they leave out several core details in the RFC definition which makes interoperability hard to set up between different vendors' routers when the protocol is used. Even Cisco NX-OS for example does not support unequal cost load balancing. As of 2022 EIGRP has alpha support in FRRouting and it seems to be generally unsupported by other routing software . Router (computing) A router

4851-785: The primary concerns. The use of TCP would cause jitter if any packets were lost as TCP does not provide subsequent data to the application while it is requesting a re-send of the missing data. Numerous key Internet applications use UDP, including: the Domain Name System (DNS), the Simple Network Management Protocol (SNMP), the Routing Information Protocol (RIP) and the Dynamic Host Configuration Protocol (DHCP). Voice and video traffic

4928-547: The rest to zero, effectively reducing the above formula to ( Bandwidth E + Delay E ) ⋅ 256 {\displaystyle ({\text{Bandwidth}}_{E}+{\text{Delay}}_{E})\cdot 256} . Obviously, these constants must be set to the same value on all routers in an EIGRP system, or permanent routing loops may result. Cisco routers running EIGRP will not form an EIGRP adjacency and will complain about K-values mismatch until these values are identical on these routers. EIGRP scales

5005-585: 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 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

5082-421: The routing table was last updated. EIGRP does not send its routing table periodically, but will only send routing table data when an actual change has occurred. This behavior is more inline with link-state routing protocols , thus EIGRP is mostly considered a hybrid protocol. When a router running EIGRP is connected to another router also running EIGRP, information is exchanged between the two routers. They form

5159-467: The routing table when a packet forwarding decision is made. 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. Others may have to be performed through the CPU as these packets need special attention that cannot be handled by an ASIC. User Datagram Protocol In computer networking ,

5236-458: The same basic formula for computing the overall metric, the only difference is that in IGRP, the formula does not contain the scaling factor of 256. In fact, this scaling factor was introduced as a simple means to facilitate backward compatility between EIGRP and IGRP: In IGRP, the overall metric is a 24-bit value while EIGRP uses a 32-bit value to express this metric. By multiplying a 24-bit value with

5313-427: The shortest path to a destination, therefore, not using them does not present any significant impairment of the network functionality. These neighbors will be re-evaluated for possible usage if the router transitions to Active state for that destination. EIGRP features load balancing on paths with different costs. A multiplier, called variance, is used to determine which paths to include into load balancing. The variance

5390-411: 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

5467-440: 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

5544-470: The vector metrics in computing the Composite metric: The composite routing metric calculation uses five parameters, so-called K values, K1 through K5. These act as multipliers or modifiers in the composite metric calculation. K1 is not equal to Bandwidth, etc. By default, only total delay and minimum bandwidth are considered when EIGRP is started on a router, but an administrator can enable or disable all

5621-401: The weighted formula. The interface delay is a configurable static parameter expressed in tens of microseconds. EIGRP takes this value directly without scaling into the weighted formula. However, various show commands display the interface delay in microseconds. Therefore, if given a delay value in microseconds, it must first be divided by 10 before using it in the weighted formula. IGRP uses

5698-412: The workload on a network administrator who does not have to configure changes to the routing table manually. In addition to the routing table , EIGRP uses the following tables to store information: Information in the topology table may be inserted into the router's routing table and can then be used to forward traffic. If the network changes (for example, a physical link fails or is disconnected),

5775-408: 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

5852-436: 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

5929-782: 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

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