Section 2 - EIGRP

feasible distance

The metric value for the lowest-metric path to reach a destination.

feasibility condition

A condition under which, for a route to be considered a backup route, the reported distance received for that route must be less than the feasible distance calculated locally. This logic guarantees a loop-free path.

feasible successor

A route that satisfies the feasibility condition and is maintained as a backup route.

hello packets

Packets that are sent out at periodic interval to detect neighbors for establishing adjacency and ensuring that neighbors are still available.

hello timer

The amount of time between hello packets being advertised out an interface.

EIGRP metric weights (K values)

Multipliers that are used in the EIGRP metric calculation. These values can be modified to change the relative weighting of the various components of the EIGRP metric formula.

reported distance

The distance reported by a router to reach a prefix; the feasible distance for the advertising router.

successor

The first next-hop router for the successor route.

successor route

The route with the lowest path metric to reach a destination.

topology table

A table used by EIGRP that maintains all network prefixes, advertising EIGRP neighbors for prefixes, and path metrics for calculating the best path.

variance value

A multiplier used to enable EIGRP unequal-cost load balancing. Any feasible successor with a metric below the FD of the current successor route, multiplied by this value, can installed into the RIB.

wide metrics

A new method of advertising and identifying interface speeds and delay to account for higher-bandwidth interfaces (20 Gbps and higher) in EIGRP.

passive route

An EIGRP route that is stable and not currently undergoing re-computation.

active route

An EIGRP route that is currently undergoing re-computation.

Reliable Transport Protocol (RTP)

A Cisco proprietary protocol used to manage the exchange of messages between EIGRP routers in a guaranteed, ordered manner.

hold time

The amount of time required for a hello packet to be received for the neighbor to be deemed healthy. Upon receipt, this value resets and decrements towards zero.

Diffusing Update Algorithm (DUAL)

A convergence algorithm used in EIGRP when a route fails and a router does not have a feasible successor route. It causes the routers to send EIGRP Query and Reply messages to discover alternate loop-free routes.

null0

A directly connected, software-only interface automatically added to EIGRP summary routes in order to prevent unnecessary forwarding of packets to unreachable destinations within the summarized range.

EIGRP named mode configuration

An EIGRP configuration mode that provides a hierarchical configuration and stores settings in three subsections: address family, interface, and topology.

address family

A method of configuring IPv4 and IPv6 routing services under the same routing process.

distribute list

A list used for filtering routes for a specific routing neighbor by using an ACL.

offset list

A list used for increasing the delay for received or advertised EIGRP routes.

active timer

A timer that keeps track of the time since an EIGRP Query message was sent to a neighbor. It has a default value of 3 minutes.

stuck in active (SIA)

An event that occurs when an EIGRP query is sent to downstream neighbors and the router doesn't receive a reply before the active timer expires.

EIGRP stub router

A router running EIGRP that limits EIGRP DUAL algorithm computations and reduces the EIGRP query scope.

split horizon

A routing loop-prevention mechanism that prevents a route from being advertised out of the same interface on which it was learned.