EIGRP

Question 1

What are the 4 components of EIGRP

Answer 1

1. Protocol-Dependent Modules
2. Reliable Transport Protocol (RTP)
3. Neighbor Discovery/Recovery
4. Diffusing Update Algorithm (DUAL)

Question 2

What is RTP?

Answer 2

RTP manages the delivery & reception of EIGRP Packets.

Question 3

What is Reliability in RTP?

Answer 3

Reliability means the delivery is guaranteed and the packets will be delivered in order by adding 2 sequence numbers in the packet. Assigned by the sending RT. Seq # is incremented by 1 w/ each packet.

Question 4

How is delivery guarenteed?

Answer 4

reliable multicast algorithm (Cisco P)

Multicast address 224.0.0.10 Each neighbor receiving a reliably multicast packet will unicast an ack.

Question 5

EIGRP multiple Packet Protocol # and packet types

Answer 5

Protocol # 88 in IP header
Hello
ACKs
Updates
Queries and Replies
Requests (depreciated)

Question 6

EIGRP Hello Packets
Unicast or multicast?
Reliable or unreliable?

Answer 6

used by nei discovery and recovery process.

Multicast and use unreliable delivery

Question 7

EIGRP ACKs
Unicast or multicast?
Reliable or unreliable?

Answer 7

Are hello packets w/ no data in them.

Always unicast and use unreliable delivery

Question 8

EIGRP Updates.
Explain unicast vs multicast.
Are updates reliable or unreliable?

Answer 8

Convey route info. TX when necessary, contain only necessary information. sent only to RTs that require the info.
Required updates by a specific RT are unicast
Required updates to multiple RTs are multicast (metric or topology change
Always use reliable delivery

Question 9

EIGRP Queries and Replies

Multicast vs unicast
Reliable vs unreliable

Answer 9

Used by DUAL finite state machine to manage its diffusing computations.

Queries can be mutli or unicast
Replies always unicast
Queries and Replies always use reliable delivery

Question 10

Explain EIGRP Deadtime

Answer 10

If any packet is reliably multicast and an ACK is not received from a neighbor, the packet will be retransmitted as a unicast to that unresponding neighbor. If an ACK is not received after 16 of these unicast retransmissions, the neighbor will be declared dead.

Question 11

What is EIGRP Mutlicast Flow Timer?

Answer 11

The time to wait for an ACK before switching from multi to unicast is specified here

Question 12

What is EIGRP RTO?

Answer 12

Retransmission Timeout. Time between subsequent unicasts is specified here

Question 13

What is EIGRP SRTT?

Answer 13

Smooth Rount-Trip Time. Both multicast flow timer and RTO are calculated for each nei from here

SRTT is the avg elapsed time, (milsec) between transmission of a packet to the nei and receipt of an ACK

Question 14

What are the two steps to configuring EIGRP?

Answer 14

1. enable EIGRP w/ the CMD #router eigrp
2. Specify each major network on which to run EIGRP w/ the netw CMD

#router e  for short
#netw x.x.x.x x.x.x.x

Question 15

EIGRP Process ID

Answer 15

Range 1 - 65535

Must be same for all EIGRP processes in all RTs that share info