Кіріспе
Диффузиялық жаңарту алгоритмі (DUAL) – Cisco компаниясының EIGRP маршруттау протоколында маршруттық циклға себеп болуы мүмкін жағдайларда белгілі бір маршруттың жаһандық түрде қайта есептелуін қамтамасыз ету үшін қолданылатын алгоритм. Оны SRI International компаниясының J. J. Garcia Luna Aceves әзірлеген. Алгоритмнің толық атауы – DUAL шекті күйдегі автомат (DUAL FSM). EIGRP автономды жүйеде маршруттандыру үшін жауапты, ал DUAL маршруттандыру топологиясындағы өзгерістерге ден қойып, маршруттандыру кестелерін автоматты түрде динамикалық түрде реттейді. EIGRP тек циклсыз маршруттардың таңдалуын қамтамасыз ету үшін мүмкіндік шартын пайдаланады. Мүмкіндік шарты консервативті: егер шарт орындалса, циклдар пайда болмайды, бірақ кейбір жағдайларда, тіпті циклсыз болса да, барлық маршруттарды қабылдаудан бас тартуы мүмкін. Егер мақсатқа жетуге қолайлы маршрут болмаса, DUAL алгоритмі желіден мәселі тудырған маршруттың барлық іздерін жою үшін диффузиялық есептеуді іске қосады. Осыдан кейін жаңа маршрутты қалпына келтіру үшін Bellman-Ford алгоритмі қолданылады.
The diffusing update algorithm (DUAL) is the algorithm used by Cisco's EIGRP routing protocol to ensure that a given route is recalculated globally whenever it might cause a routing loop. It was developed by J. J. Garcia Luna Aceves at SRI International. The full name of the algorithm is DUAL finite state machine (DUAL FSM). EIGRP is responsible for the routing within an autonomous system, and DUAL responds to changes in the routing topology and dynamically adjusts the routing tables of the router automatically. EIGRP uses a feasibility condition to ensure that only loop free routes are ever selected. The feasibility condition is conservative: when the condition is true, no loops can occur, but the condition might under some circumstances reject all routes to a destination although some are loop free. When no feasible route to a destination is available, the DUAL algorithm invokes a diffusing computation to ensure that all traces of the problematic route are eliminated from the network. At which point the normal Bellman–Ford algorithm is used to recover a new route.
Операция
DUAL маршрутты есептеу үшін үш бөлек кесте қолданады. Бұл кестелер EIGRP маршрутизаторлары арасында алмасылатын ақпарат арқылы құрылады. Ақпарат байланыс жағдайының маршруттау протоколдарымен алмасылатын ақпараттан өзгеше. EIGRP-де алмасылатын ақпаратқа маршруттар, әрбір маршруттың "метрикасы" немесе құны, сондай-ақ көршілік қатынасты құру үшін қажетті ақпарат (AS нөмірі, таймерлер және K мәндері сияқты) кіреді. Үш кесте және олардың функциялары егжей-тегжейлі келесідей:
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Көрші кестеде басқа барлық тікелей қосылған маршрутизаторлар туралы ақпарат бар. Әр қолданылатын протокол үшін жеке кесте бар (IP, IPX және т.б.). Әрбір жазба желі интерфейсі мен мекенжайының сипаттамасымен көршісіне сәйкес келеді. Сонымен қатар, байланыс тірі ме, жоқ па, оны кезең-кезеңмен анықтау үшін таймер басталады. Бұл "Саламдасу" пакеттері арқылы жүзеге асырылады. Егер "Саламдасу" пакеті көршіден белгілі бір уақыт ішінде алынбаса, маршрутизатор істен шығарылып, көрші кестеден өшіріледі.
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Топология кестесі автономды жүйедегі кез келген бағытқа барлық маршруттардың метрикасын (құн туралы ақпаратты) қамтиды. Бұл ақпарат көрші кестеде орналасқан көрші маршрутизаторлардан алынады. Бастапқы (мұрагер) және екінші (болуы мүмкін мұрагер) маршруттар топология кестесіндегі ақпарат арқылы анықталады. Топология кестесінің әрбір жазбасында келесі мәліметтер бар:
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
"FD (Feasible Distance)": Автономды жүйедегі мақсатқа жету жолының есептелген метрикасы.
"RD (Reported Distance)": Көрші маршрутизатор жариялаған бағытқа арналған метрика. RD, FD есептеу үшін және маршруттың "іске асырылу шарты" орындалатынын анықтау үшін қолданылады.
Маршруттың жағдайы: Маршрут "белсенді" немесе "бейбелсенді" деп белгіленеді. "Бейбелсенді" маршруттар тұрақты және деректерді беру үшін пайдаланылуы мүмкін. "Белсенді" маршруттар қайта есептеледі және/немесе қол жетімді емес.
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Маршруттау кестесі (негізгі "метрика" бойынша) бағытқа жетудің ең жақсы маршрутын қамтиды. Бұл маршруттар топология кестесінің мұрагерлері болып табылады. DUAL топология кестесінен басқа маршрутизаторлардан алынған деректерді бағалайды және бастапқы (мұрагер) және екінші (болуы мүмкін мұрагер) маршруттарды есептейді. Негізгі жол әдетте мақсатқа жету үшін ең төменгі метрикасы бар жол, ал резервтік жол – екінші ең төменгі құны бар жол (егер ол іске асырылу шартын орындаса). Бірнеше мұрагерлер және бірнеше болуы мүмкін мұрагерлер болуы мүмкін. Мұрагерлер мен болуы мүмкін мұрагерлер топология кестесінде сақталады, бірақ маршруттау кестесіне тек мұрагерлер қосылады және пакеттерді маршруттау үшін қолданылады.
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Маршруттың болуы мүмкін мұрагер болуы үшін, оның RD-і мұрагердің FD-інен кіші болуы керек. Егер осы іске асырылу шарты орындалса, маршруттау кестесіне осы маршрутты қосу циклға әкелмейді. Егер мақсатқа жету үшін барлық мұрагер маршруттары сәтсіз болса, болуы мүмкін мұрагер мұрагер болады және дереу маршруттау кестесіне қосылады. Егер топология кестесінде болуы мүмкін мұрагер болмаса, жаңа маршрутты іздеу үшін сұрау процесі басталады.
DUAL uses three separate tables for the route calculation. These tables are created using information exchanged between the EIGRP routers. The information is different than that exchanged by link state routing protocols. In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values). The three tables and their functions in detail are as follows:
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.
Neighbor table contains information on all other directly connected routers. A separate table exists for each supported protocol (IP, IPX, etc.). Each entry corresponds to a neighbour with the description of network interface and address. In addition, a timer is initialized to trigger the periodic detection of whether the connection is alive. This is achieved through "Hello" packets. If a "Hello" packet is not received from a neighbor for a specified time period, the router is assumed down and removed from the neighbor table. Topology table contains the metric (cost information) of all routes to any destination within the autonomous system. This information is received from neighboring routers contained in the Neighbor table. The primary (successor) and secondary (feasible successor) routes to a destination will be determined with the information in the topology table. Among other things, each entry in the topology table contains the following:
"FD (Feasible Distance)": The calculated metric of a route to a destination within the autonomous system. "RD (Reported Distance)": The metric to a destination as advertised by a neighboring router. RD is used to calculate the FD, and to determine if the route meets the "feasibility condition". Route Status: A route is marked either "active" or "passive". "Passive" routes are stable and can be used for data transmission. "Active" routes are being recalculated, and/or not available. Routing table contains the best route(s) to a destination (in terms of the lowest "metric"). These routes are the successors from the topology table. DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes. The primary path is usually the path with the lowest metric to reach the destination, and the redundant path is the path with the second lowest cost (if it meets the feasibility condition). There may be multiple successors and multiple feasible successors. Both successors and feasible successors are maintained in the topology table, but only the successors are added to the routing table and used to route packets. For a route to become a feasible successor, its RD must be smaller than the FD of the successor. If this feasibility condition is met, there is no way that adding this route to the routing table could cause a loop. If all the successor routes to a destination fail, the feasible successor becomes the successor and is immediately added to the routing table. If there is no feasible successor in the topology table, a query process is initiated to look for a new route.