EIGRP

Question 1

EIGRP Traits
(9 points)

Answer 1

1) Enhanced Interior Gateway Routing Protocol
2) distance vector / link-state hybrid
3) initially Cisco-proprietary, but defined in open RFC 7868
4) Diffusing Update Algorithm (DUAL)
5) No broadcasts
6) Partial updates
7) supports IPv4, IPv6, IPX and Appletalk (deprecated), dial plan for VoIP, and SAF
8) Classless
9) Unequal metric load balancing

Question 2

EIGRP Multicast Address

Answer 2

1) 224.0.0.10 for IPv4
2) FF02::A for IPv6

Question 3

EIGRP Protocol

Answer 3

Protocol 88, using Reliable Transport Protocol (RTP)
TCP-6
UDP-17

Question 4

EIGRP Tables

Answer 4

1) Neighbor
2) Topology
3) Routing
4) Separate neighbor and topology table per routed protocol (e.g. IPv4, IPv6)

Question 5

EIGRP Neighbor Table Info

Answer 5

1) Neighbor’s primary IP
2) Directly connected interface to neighbor

Question 6

EIGRP Topology Table Info

Answer 6

1) All destination routes advertised by neighbors
2) The metric for each neighbor advertising a destination

Question 7

EIGRP Metric Calculation

Answer 7

Sum of the advertised metric from the neighbor plus the link cost to the neighbor

Question 8

EIGRP Successor
(3 points)

Answer 8

1) The route with the best metric to the destination
2) Added to routing table
3) Advertised to other neighbors

Question 9

EIGRP Feasible Successor (FS)

Answer 9

Best alternative loop-free backup path to reach a destination

Question 10

EIGRP High Level Process For Neighbor Discovery

Answer 10

1) R1 sends hellos through all EIGRP-enabled interfaces
2) R2 neighbor receives hello and replies with its own hello
3) Each router replies with an ACK and neighbor adjacencies are established

Question 11

EIGRP High Level Process For Route Updates

Answer 11

1) R2 can send updates at the same time it sends the hello
2) Once neighboring is complete, R1 can send an ACK for the updates
3) R1 can send its own updates to R2
4) R2 sends an ACK

Question 12

EIGRP Packet Types

Answer 12

1) Hello
2) Update
3) Query
4) Requests
5) Reply
6) Acknowledge

Question 13

EIGRP Hello Packets
(What they do?)
(How are they sent?)
(What are the contents?)

Answer 13

1) Discovers neighbors to establish adjacencies
2) Sent as multicasts and contain ACK number of 0
3) Contains AS, K values, primary subnet, and authentication info

Question 14

EIGRP Update Packets
(4 points)

Answer 14

1) Communicates routes that router has used to converge
2) Sent as multicasts when a new route is discovered or when convergence is completed
3) Sent as unicasts when sychronizing topology tables with new neighbors upon EIGRP startup
4) Sent reliably between EIGRP routers

Question 15

EIGRP Query Packets

Answer 15

1) Used to query other EIGRP neighbors for a FS when EIGRP is recomputing a route that’s missing an FS
2) Advertises that a route is in an ACTIVE state and the originator is requesting alternate path info
3) Sent reliably as multicasts

Question 16

EIGRP Request Packets
(4 points)

Answer 16

1) Used to get specific info from neighbors
2) Used in route server applications
3) Can be multicast or unicast
4) Transmitted unreliably

Question 17

EIGRP Reply Packets

Answer 17

1) Sent as the response to a Query packet
2) Sent reliably as unicasts to the originator of the query

Question 18

EIGRP Acknowledge Packets

Answer 18

1) Used to acknowledge Updates, Queries, and Replies
2) ACK are hello packets that contain no data and a non-zero acknowledgement number
3) Sent as unicasts

Question 19

EIGRP Route Statuses

Answer 19

1) Active - the router is performing recomputation to seek for a new successor when the existing successor has become invalid
2) Passive - the router is not performing recomputation for that route

Question 20

EIGRP Neighbor Adjacency Requirements

Answer 20

1) Matching AS Number
2) Matching K values
3) Matching primary subnet
4) Authentication method and password
5) Communicating interface isn’t passive

Question 21

EIGRP AS Best Practice

Answer 21

Match BGP ASN, or if no BGP, set them all to 1

Question 22

EIGRP passive-interface command

Answer 22

Suppresses the exchange of hello packets, both ingress, and egress

Question 23

EIGRP K Values

Answer 23

K1 - Bandwidth, default 1. Smallest BW of all outgoing interfaces between src and st, in kilobits
K2 - Load, default 0. Worst load on link btwn src & dst
K3 - Delay, default 1. Sum of all interface delay along the path, in tens of microseconds
K4 - Reliability, default 0. Likelihood of successful packet transmission, from 0 to 255, where 255 means 100% reliable
K5 - MTU, default 0. Smallest MTU in path in bytes
K6 - introduced in wide-metrics for future use, default 0

Question 24

EIGRP Bandwidth

Answer 24

1) BW = 10^7/min (Advertised_BW, Link_BW)

Question 25

EIGRP Delay

Answer 25

1) delay = sum(Advertised_delay, Link_delay)
2) Only cumulative metric so best choice to manipulate for traffic engineering

Question 26

EIGRP Metric

Answer 26

Metric = (BW + delay)*256

Question 27

EIGRP-Wide Metrics

Answer 27

1) high-speeds interfaces looked like 1g ports according to metrics, so new formula was needed
2) supports 64-bit metric calculations and RIB scaling up to about 4.2 terabits
3) 65536 is the wide-scale constant

Question 28

metric rib-scale

Answer 28

1) sets the RIB scaling factor for EIGRP
2) all EIGRP routes in RIB are cleared and replaced with new metric values

Question 29

EIGRP MTU

Answer 29

1) never used for metric calculation
2) only used as a tiebreaker when the router needs to ignore some equal-cost paths
3) route with the highest MTU is preferred

Question 30

EIGRP Advertised Distance (AD) aka Reported Distance (RD)

Answer 30

EIGRP metric for a neighbor to reach a destination network

Question 31

EIGRP Feasible Distance (FD)

Answer 31

1) metric for the local router to reach a destination
2) advertised distance + metric to reach the neighbor
3) lowest FD gets installed into the routing table if its Administrative Distance wins

Question 32

EIGRP Successor Route

Answer 32

route with the lowest Feasible Distance that is installed in the routing table

Question 33

EIGRP Feasible Successor Route

Answer 33

1) a next-hop router must have an AD that is less than the FD of the current successor route
2) this rule ensures the network is loop-free
3) when Successor route fails, DUAL uses the FS route to avoid recomputing the route

Question 34

maximum-paths

Answer 34

1) used to enable Equal-Cost multipathing (ECMP)
2) up to 4 routes are installed in the routing table
3) max number of routes the same dst varies on the device platform
4) can be used with EIGRP, OSPF, and RIP
5) value range from 1 to 16, where 4 is the default
6) route-based load balancing is done on a conversation basis, not per packet
7) must be configured the same on both sides of the path

Question 35

EIGRP Unequal-cost Load Balancing

Answer 35

1) turned off by default
2) can load balance through paths that offer up to 128 times worse metrics than the successor route

Question 36

variance

Answer 36

1) default is 1
2) tell EIGRP to install routes as long as it’s less than the current cost multiplie by the variance

Question 37

traffic-share

Answer 37

1) balanced - the router distributes traffic proportionally to the ratios of the metrics
2) min - traffic is sent only across the minimum cost path even when multiple paths are in the routing table; variance + min can help add feasible routes to the routing table improve convergence

Question 38

EIGRP for IPv6

Answer 38

1) easy to configure
2) Advanced distance vector mechanism with some link-state features
3) Protocol-dependent modules
4) Supports IPv6 as a separate routing context
5) Adjacencies and next-hop attributes use link-local addresses
6) Configured over a link – there is no network statement