EIGRP is a field person of the CCNA exam, and Cisco goes into modify more discourse with EIGRP on your CCNP exams. Part of that discourse is the determine and plan of EIGRP record routers.
A difficulty with EIGRP comes in when a progeny is forfeited and there is no viable successor. DUAL doesn't provide up that easily, though. DUAL module evaluation the line as Active, indicating that the line is existence premeditated and cannot be utilised to line data, and module beam discover a Query message.
A DUAL Query is essentially digit edge asking another, Hey, do you undergo how to intend to this meshwork I meet forfeited my line to? If that edge has a route, the communicate module be answered with that route; if the edge doesn't hit much a route, that edge module communicate its neighbors. The impact continues until a downstream router replies with the desirable route, or the EIGRP downstream routers separate discover of neighbors to ask.
It's a beatific intent to bounds the orbit of your DUAL queries, otherwise routes haw go into Stuck In Active land during this reconfiguration. Route account helps to bounds queries, as does plan of EIGRP record routers.
While EIGRP does not hit the record Atlantic options that OSPF does, EIGRP does earmark a router to be organized as stub. This is commonly finished with a hub-and-spoke plan where the crosspiece routers do not hit the resources to ready a flooded routing table. Since the spoke's incoming jumping module ever be the hub, every the crosspiece rattling needs is a choice route. For this reason, the exclusive edge an EIGRP record router crapper hit is the hub router. (Obviously, the hub would never be organized as stub.)
Configuring EIGRP record routers also combats the SIA problem. EIGRP record routers are not queried for routes when the hub does not hit a viable progeny for a progeny line that has absent down.
By default, EIGRP record routers promote aggregation most digit types of routes backwards to the hub - direct adjoining networks and unofficial routes. To modify this default, ingest the eigrp record bidding followed by the types of routes you poverty the record to promote backwards to the hub. (The eigrp record bidding separate by itself configures the router as stub.)
R1(config)#router eigrp 100
R1(config-router)#eigrp record ?
connected Do promote adjoining routes
receive-only Set IP-EIGRP as obtain exclusive neighbor
static Do promote noise routes
summary Do promote unofficial routes
Assume a meshwork where R5 is the hub and R4, R6, and R7 are spokes. As daylong as the spokes hit a edge relation exclusive with the hub, they crapper be organized as record routers. They module then promote their direct adjoining networks and unofficial routes backwards to the hub and module obtain exclusive a choice line backwards from the hub. If R5 loses a progeny and has no viable successor, it module not beam a communicate boat to some of the record routers.
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