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Persistent Routing Loop
A routing loop is a common problem with various types of Network theory, networks, particularly computer networks. They are formed when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destination forms a loop. In the simplest version, a routing loop of size two, Node (computer science), node A thinks that the path to some destination (call it C) is through its neighbouring node, node B. At the same time, node B thinks that the path to C starts at node A. Thus, whenever traffic for C arrives at either A or B, it will loop endlessly between A and B, unless some mechanism exists to prevent that behaviour. How a routing loop can form For example, in this illustration, node A is transmitting data to node C via node B. If the link between nodes B and C goes down and B has not yet informed node A about the breakage, node A transmits the data to node B assuming that the link A-B-C is operational and of lowest cost. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Theory
In mathematics, computer science, and network science, network theory is a part of graph theory. It defines networks as Graph (discrete mathematics), graphs where the vertices or edges possess attributes. Network theory analyses these networks over the symmetric relations or directed graph, asymmetric relations between their (discrete) components. Network theory has applications in many disciplines, including statistical physics, particle physics, computer science, electrical engineering, biology, archaeology, linguistics, economics, finance, operations research, climatology, ecology, public health, sociology, psychology, and neuroscience. Applications of network theory include Logistics, logistical networks, the World Wide Web, Internet, gene regulatory networks, metabolic networks, social networks, epistemological networks, etc.; see List of network theory topics for more examples. Euler's solution of the Seven Bridges of Königsberg, Seven Bridges of Königsberg problem is c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enhanced Interior Gateway Routing Protocol
Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers. In 2013, Cisco permitted other vendors to freely implement a limited version of EIGRP with some of its associated features such as High Availability (HA), while withholding other EIGRP features such as EIGRP stub, needed for DMVPN and large-scale campus deployment. Information needed for implementation was published with informational status as in 2016, which did not advance to Internet Standards Track level, and allowed Cisco to retain control of the EIGRP protocol. 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Holddown
Holddown works by having each router start a timer when it first receive information about a network that is unreachable. Until the timer expires, the router will discard any subsequent route messages that indicate the route is actually reachable. It can resolve situations where multiple routers are connected indirectly. There are realistic scenarios where split horizon and split horizon with poisoned reverse are ineffective. In other words, a holddown prevents a router from receiving route updates until the network appears to be stable—until either an interface stops changing state (flapping) or a better route is learned. Holddowns are typically implemented with timer A timer or countdown timer is a type of clock that starts from a specified time duration and stops upon reaching 00:00. It can also usually be stopped manually before the whole duration has elapsed. An example of a simple timer is an hourglass ...s. If the router detects that a network is unreachable, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Route Poisoning
Route poisoning is a method to prevent a Router (computing), router from sending packets through a route that has become invalid within computer networks. Distance-vector routing protocols in computer networks use route poisoning to indicate to other routers that a route is no longer reachable and should not be considered from their routing tables. Unlike the ''split horizon with poison reverse'', route poisoning provides for sending updates with unreachable Hop (telecommunications), hop counts immediately to all the nodes in the network. When the protocol detects an invalid route, all of the routers in the network are informed that the bad route has an infinite (∞) route metric. This makes all nodes on the invalid route seem infinitely distant, preventing any of the routers from sending Network packet, packets over the invalid route. Some distance-vector routing protocols, such as Routing Information Protocol, RIP, use a maximum hop count to determine how many routers the traffic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Split Horizon Route Advertisement
In computer networking, split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned. The concept was suggested in 1974 by Torsten Cegrell, and originally implemented in the ARPANET-inspired Swedish network TIDAS. Terminology Here is some basic terminology: * Route poisoning: if a node N learns that its route to a destination D is unreachable, inform that to all nodes in the network by sending them a message stating that the distance from N to D, as perceived by N, is infinite. * Split horizon rule: if a node N uses interface I to transmit to a given destination D, N should not send through I new information about D. * Poison reverse rule: if a node N uses interface I to transmit to a given destination D, N sends through I the information that its cost-to-go to D is infinite. Whereas under split horizon N does not send any in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interior Gateway Routing Protocol
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 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.{{cite web , url=https://www.iana.org/assignments/protocol-numbers/protocol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Routing Information Protocol
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. RIP implements the split horizon, route poisoning, and holddown mechanisms to prevent incorrect routing information from being propagated. In RIPv1 routers broadcast updates with their routing table every 30 seconds. In the early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times. In most networking environments, RIP is not the preferred choice of routing protocol, as its time to converge and scalability are poo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Babel (protocol)
The Babel routing protocol is a distance-vector routing protocol for Internet Protocol packet-switched networks that is designed to be robust and efficient on both wireless mesh networks and wired networks. Babel is described in RFC 8966. Babel is based on the ideas in Destination-Sequenced Distance Vector routing (DSDV), Ad hoc On-Demand Distance Vector Routing (AODV), and Cisco Cisco Systems, Inc. (using the trademark Cisco) is an American multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, s ...'s Enhanced Interior Gateway Routing Protocol (EIGRP), but uses different techniques for loop avoidance. Babel has provisions for using multiple dynamically computed metrics; by default, it uses hop-count on wired networks and a variant of expected transmission count on wireless links, but can be configured to take radio diversity into account or to aut ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Destination-Sequenced Distance Vector Routing
Destination-Sequenced Distance-Vector Routing (DSDV) is a table-driven routing scheme for ad hoc mobile networks based on the Bellman–Ford algorithm. It was developed by C. Perkins and P. Bhagwat in 1994. The main contribution of the algorithm was to solve the routing loop problem. Each entry in the routing table contains a sequence number, the sequence numbers are generally even if a link is present; else, an odd number is used. The number is generated by the destination, and the emitter needs to send out the next update with this number. Routing information is distributed between nodes by sending ''full dumps'' infrequently and smaller incremental updates more frequently. For example, the routing table of Node A in this network is Naturally the table contains description of all possible paths reachable by node A, along with the next hop, number of hops and sequence number. Selection of Route If a router receives new information, then it uses the latest sequence number. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Distance-vector Routing Protocol
A distance-vector routing protocol in data networks determines the best route for data packets based on distance. Distance-vector routing protocols measure the distance by the number of routers a packet has to pass; one router counts as one hop. Some distance-vector protocols also take into account network latency and other factors that influence traffic on a given route. To determine the best route across a network, routers using a distance-vector protocol exchange information with one another, usually routing tables plus hop counts for destination networks and possibly other traffic information. Distance-vector routing protocols also require that a router inform its neighbours of network topology changes periodically. 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 vec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Network
A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or by wireless communication. The devices may be connected in a variety of network topologies. In order to communicate over the network, computers use agreed-on rules, called communication protocols, over whatever medium is used. The computer network can include personal computers, Server (computing), servers, networking hardware, or other specialized or general-purpose Host (network), hosts. They are identified by network addresses and may have hostnames. Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying the nodes by communication protocols such as the Internet Protocol. Computer networks may be classified by many criteria, including the tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IS-IS
Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this by determining the best route for data through a packet switching network. The IS-IS protocol is defined in ISO/IEC 10589:2002 as an international standard within the Open Systems Interconnection (OSI) reference design. In 2005, IS-IS was called "the ''de facto'' standard for large service provider network backbones". Description IS-IS is an interior gateway protocol, designed for use within an administrative domain or network. This is in contrast to exterior gateway protocols, primarily Border Gateway Protocol (BGP), which is used for routing between autonomous systems. IS-IS is a link-state routing protocol, operating by reliably flooding link state information throughout a network of routers. Each IS-IS router independent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
