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Flashcards in EIGRP Deck (57):

What is an EIGRP query, and what is it used for?

An EIGRP query is sent when the successor is gone and the feasible successor is not available. An EIGRP query is used so that EIGRP can have fast convergence.


What is the meaning of the term active route?

Active routes are routes in which the primary path is gone and no feasible successors are available. The router is actively searching for an alternate path.


What is a feasible successor?

A feasible successor is an EIGRP neighbor that does not satisfy the feasible condition. Feasible successors can also be thought of as EIGRP backup routes that are used when the primary route is gone.


What is EIGRP's multicast address?

EIGRP's multicast address is


What is the feasible condition?

The feasible condition is a condition in which the reported distance is less than the feasible distances. This condition ensures a loop-free topology.


What is stuck in active?

Stuck in active is a condition in which the router has sent out queries for a lost route and has not received a reply within the active timer. By default, the active timer is three minutes.


Is EIGRP a distance vector or a link-state routing protocol?

EIGRP is a distance vector protocol.


What is the maximum configured bandwidth EIGRP will use on a link? Can this percentage be changed?

By default, EIGRP uses no more than 50 percent of the link’s bandwidth, based on the bandwidth configured on the router’s interface. This percentage can be changed with the command ip bandwidth-percent eigrp.


How do EIGRP and IGRP differ in the way they calculate the composite metric?

EIGRP and IGRP use the same formula to calculate their composite metrics, but EIGRP scales the metric by a factor of 256.


What are the four basic components of EIGRP?

The Protocol Dependent Modules

The Reliable Transport Protocol

The Neighbor Discovery and Recovery Module

The Diffusing Update Algorithm


In the context of EIGRP, what does the term reliable delivery mean? Which two methods ensure reliable delivery of EIGRP packets?

Reliable delivery means EIGRP packets are guaranteed to be delivered, and they are delivered in order. RTP uses a reliable multicast, in which received packets are acknowledged, to guarantee delivery; sequence numbers are used to ensure that they are delivered in order.


Which mechanism ensures that a router is accepting the most recent route entry?

Sequence numbers ensure that a router is receiving the most recent route entry.


What are the packet types used by EIGRP?









At what interval, by default, are EIGRP Hello packets sent?

Hello interval is 5 seconds, except on some slow-speed (T1 and below) interfaces, where the default is 60 seconds.


What is the default hold time?

The EIGRP default hold time is three times the Hello interval.


What is the difference between the neighbor table and the topology table?

The neighbor table stores information about EIGRP-speaking neighbors; the topology table lists all known routes that have feasible successors.


What is a feasible distance?

router’s lowest calculated distance to the destination


What is a successor?

a feasible successor that is currently being used as the next hop to the destination.


What is the difference between an active route and a passive route?

route is active on a particular router if the router has queried its neighbors for a feasible successor and has not yet received a reply from every queried neighbor. The route is passive when there are no outstanding queries.


What causes a passive route to become active?

A route becomes active when no feasible successor exists in its topology table.


What causes an active route to become passive?

An active route becomes passive when a reply has been received from every queried neighbor.


What is the difference between subnetting and address aggregation?

Subnetting is the practice of creating a group of subnet addresses from a single IP network address. Address aggregation is the practice of summarizing a group of network or subnet addresses with a single IP network address.


Define hello interval (EIGRP)

With some routing protocols, the time period between successive Hello messages.


Define full update (EIGRP)

A routing protocol feature by which the routing update includes the entire set of routes, even if some or all of the routes are unchanged.


Define partial update

A routing protocol feature by which the routing update includes only routes that have changed, rather than include the entire set of routes.


Define Route tag field

A field within a route entry in a routing update, used to associate a generic number with the route. It is used when passing routes between routing protocols, allowing an intermediate routing protocol to pass information about a route that is not natively defined to that intermediate routing protocol. Frequently used for identifying certain routes for filtering by a downstream routing process.


Define Next hop field

With a routing update, or routing table entry, the portion of a route that defines the next router to which a packet should be sent to reach the destination subnet. With routing protocols, the Next Hop field may define a router other than the router sending the routing update.


Define MD5

A method of applying a mathematical formula, with input including a private key, the message contents, and sometimes a shared text string, with the resulting digest being included with the message. The sender and the receiver perform the same math to allow authentication and to prove that no intermediate device changed the message contents.


Define DUAL

A term referring to EIGRP’s internal processing logic.


Define Hold timer (EIGRP)

the timer used to determine when a neighboring router has failed, based on a router not receiving any EIGRP messages, including Hellos, in this timer period.


Define K value

EIGRP (and IGRP) allows for the use of bandwidth, load, delay, MTU, and link reliability; the K values refer to an integer constant that includes these five possible metric components. Only bandwidth and delay are used by default, to minimize recomputation of metrics for small changes in minor metric components.


Define Neighbor (EIGRP)

With EIGRP, a router sharing the same primary subnet, with which Hellos are exchanged, parameters match, and with which routes can be exchanged.


Define Adjacency (EIGRP)

Often used synonymously with neighbor, but with emphasis on the fact that all required parameters match, allowing routing updates to be exchanged between the routers.


Define RTP

A protocol used for reliable multicast and unicast transmissions. Used by EIGRP.


Define SRTT

With EIGRP, a purposefully slowly changing measurement of round-trip time between neighbors, from which the EIGRP RTO is calculated.


Define RTO

ith EIGRP, a timer started when a reliable (to be acknowledged) message is transmitted. For any neighbor(s) failing to respond in its RTO, the RTP protocol causes retransmission. RTO is calculated based on SRTT.


Define Update (EIGRP)

An EIGRP message that informs neighbors about routing information. Update messages require an Ack.


Define Ack (EIGRP)

An EIGRP message that is used to acknowledge reliable EIGRP messages, namely Update, Query, and Reply messages. Acks do not require an Ack.


Define query (EIGRP)

An EIGRP message that is used to ask neighboring routers to verify their route to a particular subnet. Query messages require an Ack.


Define Reply (EIGRP)

An EIGRP message that is used by neighbors to reply to a query. Reply messages require an Ack.


Define Hello (EIGRP)

An EIGRP message that identifies neighbors, exchanges parameters, and is sent periodically as a keepalive function. Hellos do not require an Ack.


Define Goodbye

An EIGRP message that is used by a router to notify its neighbors when the router is gracefully shutting down.


Define RD

the metric (distance) of a route as reported by a neighboring router.


Define FD

the metric value for the lowest-metric route to a particular subnet.


Define feasibility condition

for a particular route, the case in which the RD is lower than the FD.


Define Successor route

the route to each destination for which the metric is the lowest of all known routes to that network.


Define Feasible successor

a route that is not a successor route, but that meets the feasibility condition; can be used when the successor route fails, without causing loops.


Define input event

Any occurrence that could change a router’s EIGRP topology table, including a received Update or Query, a failed interface, or the loss of a neighbor.


Define Local computation

An EIGRP router’s reaction to an input event, leading to the use of a feasible successor or going active on a route.


Define Active

A state for a route in an EIGRP topology table that indicates that the router is actively sending Query messages for this route, attempting to validate and learn the current best route to that subnet.


Define Passive

A state for a route in an EIGRP topology table that indicates that the router believes that the route is stable, and it is not currently looking for any new routes to that subnet.


Define going active

EIGRP jargon meaning that EIGRP has placed a route into active status.


Define Stuck-in-active

The condition in which a route has been in an EIGRP active state for longer than the router’s Active timer.


Define Query scope

The characterization of how far EIGRP Query messages flow away from the router that first notices a failed route and goes active for a particular subnet.


Define EIGRP stub router

router that should not be used to forward packets between other routers. Other routers will not send Query messages to a stub router.


Define limiting query scope

An effort to reduce the query scope with EIGRP, using route summarization or EIGRP stub routers.


Define variance

An integer setting for EIGRP and IGRP. Any FS route whose metric is less than this variance multiplier times the successor’s metric is added to the routing table, within the restrictions of the maximum-paths command.