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43 Cards in this Set

  • Front
  • Back
EIGRP is a LS or DV protocol?
Neither, it is a hybrid
EIGRP is open standards / propietary?
Topology table
A table that contains all the paths advertised by neighbors to all the known networks. This is a list of all the successors, feasible successors, the feasible distance, the advertised distance, and the outgoing interface. DUAL acts on the topology table to determine successors and feasible successors by which to build a routin table.
when is a update sent?
• When a neighbor first comes up
• When a neighbor transitions from active to passive for a
• When there is a change in calculated metric for a destination
Sent from the router when it loses a path to a network. If there is no alternate route (feasible successor), it will send out queries to neighbors inquiring whether they have a feasible successor.
Smooth Round-Trip Time
The time that the router waits after sending a packet reliably to hear an acknowledgment. This is held in the neighbor table and is
used to calculate the RTO.
Retransmission Timeout
Timer calculated in reference to the SRTT. RTO determines howlong the router waits for an ACK before retransmitting the packet.
Reliable Transport Protocol
Mechanism used to determine requirements that the packets be
delivered in sequence and guaranteed.
Diffusing Update Algorithm
An algorithm performed on the topology table to converge the
network. It is based on a router detecting a network change within a finite time, with the change being sent reliably and in sequence.
As the algorithm is calculated simultaneously, in order, and
within a finite time frame on all affected routers, it ensures a loop-free network.
Advertised distance
The cost of the path to the remote network from the neighbor (the metric from the next-hop router).
Feasible distance
The lowest-cost distance (metric) to a remote network.
Feasible condition
When a neighbor reports a path cost (AD) that is lower than the
router’s FD to a network.
Feasible successor
The neighbor reporting the AD that is lower than the router’s FD becomes the feasible successor. The next-hop router that meets
the FC.
The next-hop router that passes the FC. It is chosen from the FSs as having the lowest metric to the remote network.
Stuck in Active
State reached when a router has sent out network packets and is waiting for ACKs from all its neighbors. The route is active until all the ACKs have been received. If they do not appear after a certain time, the router is SIA for the route.
Query scoping
Network design to limit the scope of the query range, that is, how far the query is allowed to propagate in search of a feasible successor. This is necessary to prevent SIA, which can cause multiple problems for the network.
Route state when there is a network change, but after examining the topology table, no FS is found. The route is set to active mode, and the router queries its neighbors for alternative routes.
An operational route is passive. If the path is lost, the router examines the topology table to find an FS. If there is an FS, it is placed in the routing table; otherwise, the router queries its neighbors, sending the route into active mode.
EIGRP increases the potential growth of a network by reducing the convergence time using what features?
■ Loop-free networks
■ Incremental updates
■ Multicast addressing for updates
■ Loop-free routing tables
■ Support for different topologies
■ Rapid convergence
■ Reduced bandwidth use
■ Protocol independence at Layer 3
■ Compatibility with IGRP
■ Easy configuration
■ Use of a composite metric
■ Unequal-cost load balancing
■ Advanced distance vector protocol
four main components of EIGRP:
■ Protocol-dependent modules
■ Neighbor discovery and recovery
There are three main tables in EIGRP:
■ The neighbor table
■ The topology table
■ The routing table
The neighbor table is maintained by means of ________
the hello protocol
The neighbor table includes the following information:
■ The address of the neighbor.
■ The interface through which the neighbor’s Hello was heard.
■ The holdtime, or how long the neighbor table waits without hearing a Hello from a neighbor,
before declaring the neighbor unavailable and purging the database. This is three times the value of the Hello timer by default.
■ The uptime, or how long since the router first heard from the neighbor.
■ The sequence number.
It tracks both the last sequence number sent to the neighbor and the last sequence number received from the neighbor.
■ SRTT. This calculates the RTO. This is the time in milliseconds that it takes a packet to be sent to a neighbor and a reply to be received.
■ RTO. This states how long the router will wait on a connection-oriented protocol without an acknowledgment before retransmitting the packet.
If the original packet that was unacknowledged was multicast, the retransmitted packets will be
The EIGRP Hello protocol uses a multicast address of
To become a neighbor, the following conditions must be met:
■ The router must hear a Hello packet or an ACK from a neighbor.
■ The autonomous system number in the packet header must be the same as that of the receiving router.
■ The neighbor’s metric settings must be the same as that of the receiving router.
The topology table includes the following information:
■ Whether the route is passive or active.
■ That an update has been sent to the neighbors.
■ That a query packet has been sent to the neighbors. If this field is positive, at least one route will
be marked as active.
■ If a query packet has been sent, another field will track whether any replies have been received from the neighbors.
■ That a reply packet has been sent in response to a query packet received from a neighbor.
■ The remote networks.
■ The prefix or mask for the remote network.
■ The metric for the remote network, the FD.
■ The metric for the remote network advertised by the next logical hop, the AD.
■ The next hop.
■ The outgoing interface to be used to reach the next logical hop.
■ The successors, the path to the remote network stated in hops.
The three reasons that might cause a topology table to be recalculated:
■ The router hears a change when a new network is available
■ The router changes the successor in the topology table and routing table
■ The router hears a change from a neighbor when a network has become unavailable
The router hears a change when a new network is available because of one of the following
— The topology table receives an update stating that there is a new remote network.
— The interface for a directly connected EIGRP network comes online.
The router changes the successor in the topology table and routing table in these circumstances:
— The topology table receives a reply or a query from a neighbor.
— There is local configuration of a directly connected interface to change the cost of the link.
The router hears a change from a neighbor when a network has become unavailable because of
one of the following reasons:
— The topology table receives a query, reply, or update stating that the remote network
is down.
— The neighbor table does not receive a Hello within the holdtime.
— The network is directly connected, and the router senses a loss of carrier.
The main difference between the metrics used in EIGRP and IGRP =
Is the calculation is held in a 32-bit field.
EIGRP Routing Types
Internal paths to the autonomous system

Internal paths that have been summarized

External paths to the autonomous system that have been redistributed into this EIGRP autonomous system
The equation for the default metric used is this:
metric = [(10000000  smallest bandwidth kbps) + sum of delays] * 256
EIGRP Metric Values:
what is the metric Delay?
The delay calculated on the outgoing interface. The value used is
the cumulative total of the delay on all the interfaces between the
hosts. The delay is measured in units of 10 ms to 168 seconds. A delay of all 1s in the 32-bit field means the network is unreachable.
The default for the K constants are
K1 = 1,
K2 = 0,
K3 = 1,
K4 = 0,
K5 = 0
The metric or cost from the neighbor advertising the route is known as the
advertised distance
The metric or cost from the router that is determining the metric or the local router is referred to as
feasible distance
A neighbor can become an FS for a route only if its __ is less than the __.
The factors that can affect the scaling of EIGRP are as follows:
■ The amount of information sent between neighbors
■ The number of routers that are sent updates
■ How far away the routers are that have to send updates
■ The number of alternative paths to remote networks
Poorly scaled EIGRP networks can result in the following:
■ A route being SIA
■ Network congestion
■ Router memory running low
■ Router CPU overutilized
■ Unreliable circuit or unidirectional link
Solutions to EIGRP Scaling Issues
■ Allocation of addresses should be contiguous to allow summarization.
■ A hierarchical tiered network design should be used to allow summarization.
■ Sufficient network resources (both hardware and software) on network devices.
■ Sufficient bandwidth should be used on WAN links.
■ Appropriate EIGRP configuration should be used on WAN links.
■ Filters should be used.
■ Network monitoring should be used.