1. Characteristics of Routing Protocols

Question 1

The amount of time for routes to failover is called what?

Answer 1

Convergence time

Question 2

A routing protocol that exchanges routes between routers in a single AS is known as what type of routing protocol?

Answer 2

IGP (interior gateway protocol)

Question 3

A routing protocol that exchanges routes between routers in a different AS is known as what type of routing protocol?

Answer 3

EGP (exterior gateway protocol)

Note: there used to be a protocol called EGP

Question 4

What are the 3 types of routing protocols based on the way they receive, advertise, and store routing info?

Answer 4

Distance-vector
Link-state
Path-vector

Question 5

How does a distance-vector routing protocol send routing updates?

Answer 5

Periodically send the full copy of its routing table even if there have been no changes.

Question 6

Distance-vector routing protocols typically use one of two approaches for preventing routing loops. What are they?

Answer 6

Split Horizon

Poison Reverse

Question 7

How does Split Horizon prevent routing loops?

Answer 7

It prevents a route learned on one interface from being advertised back out of that same interface.

Question 8

How does Poison Reverse prevent routing loops?

Answer 8

It causes a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite.

Question 9

Name two distance-vector routing protocols.

Answer 9

RIP

EIGRP

Question 10

EIGRP is know termed as an advanced distance-protocol because of enhancements. How did EIGRP improve routing advertisement?

Answer 10

It does not periodically send out its entire IP routing table to its neighbors. Instead it uses triggered updates, and it converges quickly.

Question 11

How does a link-state routing protocol send routing updates?

Answer 11

Routers send link-state advertisements (LSA) to advertise the networks they know how to reach. They send the full list only the first time and then only update the changes when they occur.

Question 12

Name the two link-state routing protocols.

Answer 12

Open Shortest Path First (OSPF)

Intermediate System–to–Intermediate System (IS-IS)

Question 13

What is the algorithm used by OSPF and IS-IS?

Answer 13

Dijkstra’s Shortest Path First

Question 14

BGP is the only EGP protocol really used today. What is the enhanced version that supports IPv6 called?

Answer 14

Multiprotocol BGP (MP-BGP)

Question 15

What does NBMA stand for?

Answer 15

Nonbroadcast multiaccess

Question 16

What IPv4 traffic type does not exist in IPv6?

Answer 16

Broadcast

Question 17

What does an IPv6 global unicat address begin with?

Answer 17

2000::/3

Question 18

What address class is an IPv4 multicast?

Answer 18

Class D

Question 19

In IPv6 networks, multicast addresses have a prefix of what?

Answer 19

ff00::/8

Question 20

One-to-nearest describes what type of IPv6 traffic?

Answer 20

Anycast

Question 21

What is the calculation for bandwidth-delay product?

Answer 21

It is calculated by multiplying the segment’s bandwidth

in bits/sec) by the latency packets experience as they cross the segment (in sec

Question 22

What is an ICMP Destination Unreachable message?

Answer 22

If a packet enters a router destined for an address that the router does not know how to reach, the router can let the sender know by sending a Destination Unreachable ICMP message back to the sender.

Question 23

What is an ICMP Redirect message?

Answer 23

A host might have routing information indicating that to reach a particular destination network, packets should be sent to a certain next-hop IP address. However, if network conditions change and a different next-hop IP address should be used, the original next-hop router can let the host know to use a different path by sending the host a Redirect ICMP message.

Question 24

What are the steps in the TCP three-way handshake?

Answer 24

Initiator sends SYN
Target send ACK plus SYN
Initiator send ACK

Question 25

What does the MSS stand for in TCP MSS?

Answer 25

Maximum Segment Size

Question 26

Does the segment size limited by TCP MSS include any headers?

Answer 26

No

Question 27

What is TCP windowing?

Answer 27

TCP will increase the number of segments sent without expecting an ACK. It will start with one segment and double the number of segments until drops happen.

Question 28

With TCP windowing, what happens when packets are dropped (and what is this called)?

Answer 28

TCP will go back to sending a single segment and doubling each time until it reaches half the number when the drop occurred.
Called TCP slow start.

Question 29

What is global synchronization?

Answer 29

A router’s queue gets filled and packets from multiple flows gets dropped causing TCP slow start on all those flows.

Question 30

What feature does Cisco support to help prevent global synchronization?

Answer 30

Weighted Random Early Detection (WRED), which can pseudo-randomly drop packets from flows based on the number of packets currently in a queue and the quality of service (QoS) markings on the packets. By dropping packets before the queue fills to capacity, the global
synchronization issue is avoided.

Question 31

What is LLQ and what does it do?

Answer 31

Low Latency Queuing allows one or more traffic types to be buffered in a priority queue, which is serviced first.