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CCIE R&S V5.1 > EIGRP > Flashcards

EIGRP Flashcards

1
Q

What does SRTT stand for?

A

Smooth Round Trip Time (SRTT)

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2
Q

What is the meaning of SRTT?

A

The average amount of time it takes for a reliable multicast to be acknowledged by a particular neighbor.

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3
Q

What is the RTO?

A

Retransmission Timeout

The amount of time in milliseconds that the router will wait for a unicast in response to a multicast as part of RTP.

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4
Q

What types of EIGRP Packets are there?

A

Hellos
Acknowledgements
Updates
Queries and Replies

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5
Q

What are EIGRP Hellos?

A

Used in neighbor discovery and recovery process. Multicast and use unreliable delivery

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6
Q

What are EIGRP Acknowledgments?

A

Hello packets with no data in them. Unicast and use unreliable delivery

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7
Q

What are EIGRP Updates?

A

Convey route information. transmitted only when needed and only to routers that need the information. When needed by multiple routers then multicast is used. Always uses reliable delivery

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8
Q

What are EIGRP Queries and Replies?

A

Used by DUAL finite state machine. Queries can be multicast or unicast, replies are always unicast. Both always use reliable delivery

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9
Q

What does DUAL stand for?

A

Diffusing Update Algorithm

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10
Q

What are the four components of EIGRP?

A
  • Protocol-Dependent Modules
  • Reliable Transport Protocol (RTP)
  • Neighbor Discovery/Recovery
  • Diffusing Update Algorithm (DUAL)
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11
Q

What is RTP?

A

Reliable Transport Protocol. Tracks the delivery of reliable multicast and makes sure messages are received in order. Send both a sequence number from the sender of each message and the last one received from the neighbor with each message.

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12
Q

What is EIGRP Protocol Number?

A

88

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13
Q

What is the EIGRP Well-Known Multicast Address?

A

224.0.0.10 or FF02::A

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14
Q

The Hello Frequency is

A
  • Hellos are usually send very 5 seconds - a small random amount of time to prevent synchronization
  • On multipoint interfaces slower than T1 hellos are unicast every 60 seconds.
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15
Q

Command: Hello interval

A

Interface level command:

ip hello-interval eigrp

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16
Q

The Hold-Time is

A

The amount of time EIGRP will wait before declaring the neighbor down. Default is 3 times the Hello interval.

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17
Q

Command: hold time

A

Interface level command:

ip hold-time eigrp

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18
Q

The Q CNT column in “show ip eigrp neighbors” is

A

Queue Count. The number of outstanding updates, queries, or replies that have not been acknowledged yet.

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19
Q

The Seq Num column in “show ip eigrp neighbors” is

A

The sequence number of the last update, query, or reply that has been sent to the neighbor

20
Q

The H column in “show ip eigrp neighbors” is

A

The order in which the neighbors were learned.

21
Q

An Adjacency is

A

A virtual link between two routers over which route information is exchanged

22
Q

How does EIGRP calculate the distance of a route?

A

It takes the advertised distance and adds it to the local link metric to that neighbor.

23
Q

What is the Feasible Distance?

A

The lowest calculated metric to a destination

24
Q

What is the Feasibility Condition?

A

The condition that is met if the neighbor’s advertised distance is less than the feasible distance to a particular destination.

25
Q

What is a Feasible Successor?

A

A neighbor that meets the Feasibility Condition (advertises a distance that is less than the feasible distance) for a particular destination. A neighbor that is one hop closer to the destination than this router.

26
Q

What is a successor?

A

The neighbor advertising the lowest metric to a destination is the successor.

27
Q

In “show ip eigrp topology” what is the first number in the parentheses?

A

The locally calculated metric

28
Q

In “show ip eigrp topology” what is the second number in the parentheses?

A

The advertised distance also known as the advertised composite metric.

29
Q

In “show IP route” what is the first number in the square brackets?

A

The Administrative Distance (AD)

30
Q

in “show ip route” what is the second number in the square brackets?

A

The metric used for the route. It is also the best metric to the route.

31
Q

When will a router reassess it’s list of feasible successors for a route?

A

Whenever an input event occurs. Input Events can be:

  • Change in the cost of a directly connected link.
  • Change in the state (up or down) of a directly connected link
  • Reception of an update packet
  • Reception of a query packet
  • Reception of a reply packet
32
Q

What is the first step in the DUAL Finite state machine?

A

Local Computation where the router recalculates the metric to all feasible successors. The possible results are:

  • If the Feasible Successor with the lowest distance is different than the existing successor then the feasible successor will become the successor.
  • If the new distance is lower than the feasible distance (FD) then the FD will be updated
  • If the new distance is different from the existing distance then updates will be sent to all neighbors.
33
Q

In the DUAL Finite State machine if a feasible successor cannot be found what happens?

A

If a feasible successor can’t be found then a diffusing computation begins and the route will be placed in Active state until it can be completed.

34
Q

While a route is active what can a router not do to the route?

A

It cannot:

  • Change the route’s successor
  • Change the distance it is advertising for the route
  • Change the route’s Feasible Distance (FD)
  • Begin another diffusing computation for the route.
35
Q

what is the Administrative Distance of a summary route?

A

5

36
Q

what is the Administrative Distance of EIGRP?

A

internal 90

external 170

37
Q

EIGRP Classic Metric Components

A

Bandwidth, Delay, Reliability, Load, MTU

38
Q

EIGRP Default K Values

A 
K1 = 1
K2 = 0
K3 = 1
K4 = 0
K5 = 0
39
Q

EIGRP classic formula

A

(k1BWs + k2BWs/(256-LOmax) + k3Ds)(K5/(k4+Rmin)
where
BWs = 25610^7/bandwidthMin
Ds = 256DelaySummed

40
Q

EIGRP classic default max link bandwidth

A

10Gbps(10^7)

41
Q

EIGRP OpCode

A 
4-bit Header value:
1=update
3=query
4=reply
5=hello/ack
10=SIA query
11=SIA reply
42
Q

SIA Query/SIA Reply

A

Stuck-In-Active query/reply are unicast to a neighbor to check if they are still working on DUAL. An SIA-query is sent and the neighbor immediately returns an SIA-reply.

43
Q

What is required for an EIGRP neighbor relationship to form?

A

EIGRP Authentication parameters must match
EIGRP K-Values must match
EIGRP Autonomous System (AS) number must match
Use of the primary address for EIGRP neighbor relationships
use of the common IP network address on a single subnet

44
Q

EIGRP Wide Metric Components

A
  • Throughput
  • Latency
  • Reliability
  • Load
  • MTU
  • Extended Metrics (Jitter, Energy, Quiscent Energy)
  • Hop Count
45
Q

EIGRP Wide Metrics default K Values

A 
K1 = 1
K2 = 0
K3 = 1
K4 = 0
K5 = 0
K6 = 0
46
Q

EIGRP Wide Metrics Formula

A

K1Tmin + K2Tmin/(256-LoMAX) + K3Lasummed + K6ExtM)(K5/(K4+Rmin))
Where
Tmin = 6553510^7/BandwidthMin(in kbps)
LaSummed = sum of 65536*DelayInterface/10^6
DelayInterface =:
* DefaultDelay in picoseconds for interfaces <= 1 Gbps or where bandwidth is configured
* 10^7 * configured delay where delay is configured.
* 10^13/defaultbandwidth for interfaces > 1 Gbps

47
Q

What is the metric rib-scale?

A

Used to scale down the wide metrics to 32 bits for the routing table. the default is 128.

CCIE R&S V5.1 (7 decks)

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