Chapter 11: BGP

Question 1

Number of unique ASNs.

Answer 1

4,294,967,295

Question 2

Private ASN range.

Answer 2

16-bit range: 64,512-65,535
32-bit range: 4,200,000,000 - 4,294,967,295

Question 3

Who is responsible for ensuring all public ASNs are globally unique?

Answer 3

IANA

Question 4

Requirements for requesting a public ASN.

Answer 4

1. Proof of a publicly allocated network range.
2. Proof that internet connectivity is provided through multiple connections.
3. Need for a unique routing policy from providers.

Question 5

______ _______ provide BGP with granularity and control of routing policies within BGP.

Answer 5

Path Attributes

Question 6

Types of BGP Path Attributes

Answer 6

Well-known mandatory
Well-known discretionary
Optional transitive
Optional non-transitive

Question 7

Which path attribute must be included with every prefix advertisement?

Answer 7

Well-known mandatory

Question 8

Which path attribute may or may not be included with a prefix advertisement?

Answer 8

Well-known discretionary

Question 9

A routing update that consists of the network prefix, prefix length, and any BGP path attributes for the specific route.

Answer 9

Network Layer Reachability Information (NLRI)

Question 10

T/F:

BGP does not contain a complete topology of the network.

Answer 10

True

Question 11

T/F:

BGP is a link-state routing protocol.

Answer 11

False

BGP is a path vector protocol.

Question 12

Attribute that includes a list of all of the ASNs that the prefix advertisement has traversed from its source.

Answer 12

AS_Path

Question 13

What is the purpose of the Address Family Identifier?

Answer 13

Advertises addresses from the specified address family to a BGP neighbor.

Question 14

What occurs when a BGP router receives a prefix advertisement with its AS listed in the AS_Path attribute?

Answer 14

The prefix advertisement is dropped because the router thinks the advertisement forms a loop.

Question 15

T/F:

BGP uses Hello packets to maintain and discover neighbors.

Answer 15

False

BGP neighbors are defined by IP addresses.

Question 16

Which port is used to communicate with other BGP routers?

Answer 16

TCP port 179

Question 17

T/F:

BGP can only form neighbor adjacencies with directly connected AS’s.

Answer 17

False

BGP can can form adjacencies with directly connected AS’s or AS’s that are multiple hops away.

Question 18

T/F:

A default route is not sufficient to establish a multi-hop BGP session.

Answer 18

True

A route between routers multiple hops away must exist in the RIB.

Question 19

2 types of BGP sessions

Answer 19

iBGP
eBGP

Question 20

iBGP administrative distance

Answer 20

200

Question 21

eBGP administrative distance

Answer 21

20

Question 22

2 scenarios that typically occur when BGP is needed within an AS.

Answer 22

1. Multiple routing policies are required.
2. Transit connectivity is provided between autonomous systems.

Question 23

eBGP default TTL

Answer 23

1

Question 24

iBGP default TTL

Answer 24

255 (allows for multi-hop sessions)

Question 25

BGP Packet Types

Answer 25

Type 1 Open Type 2 Update Type 3 Notification Type 4 Keepalive

Question 26

BGP packet used to establish an adjacency.

Answer 26

Open

Question 27

BGP packet used to advertise any feasible routes, withdraw previously advertised routers.

Answer 27

Update

Question 28

T/F: BGP does not rely on the TCP connection state to ensure that neighbors are still alive.

Answer 28

True

Question 29

BGP packet used to verify neighbors are still alive.

Answer 29

Keepalive

Question 30

Sent when an error is detected with the BGP session.

Answer 30

Notification

Question 31

Components of the Open packet.

Answer 31

BGP Version Number ASN of Originating Router Hold Time BGP Identifier

Question 32

T/F: Hold timer must be either zero or at least 3 seconds.

Answer 32

True

Question 33

Default keepalive / Default hold time

Answer 33

60 seconds / 180 seconds

Question 34

What does BGP use to maintain a table of all BGP peers and their operational status?

Answer 34

Finite State Machine

Question 35

BGP Neighbor States

Answer 35

1. Idle 2. Connect 3. OpenSent 4. OpenConfirm 5. Established 6. Updates

Question 36

BGP Path Attributes

Answer 36

Local_Pref Origin AS_Path Next_Hop Multi_Exit_Disc Atomic_Aggregate Aggregator

Question 37

Which neighbor state: - initializes all BGP resources for the peer connection. - sets ConnectRetryCounter to zero. - starts the ConnectRetryTimer with the initial value. - initiates a TCP connection to the other BGP peer - listens for a connection that may be initiated by the remote BGP peer

Answer 37

Idle