This question to reviews BGP concepts listed in the CCIE blueprint at Cisco routers.

The BGP design concepts include the following: neighbors, decision algorithm, iBGP, eBGP, peer groups, route reflectors, confederations, attributes, autonomous systems, route maps, and filters.

1 A router has the following configuration. Which routing protocol are you using?
router bgp 10
neighbor 1.1.1.1 remote-as 10

a. OBGP with an external neighbor
b. BGP with an internal neighbor
c. BGP with an external neighbor
d. EIGRP with an internal neighbor

Answer: b
The router’s BGP AS number is 10 and the BGP neighbor’s AS is 10.

2 MED is used for which of the following functions?

a. To give a hint to the routers on what outbound path to take
b. To give a hint to the confederation routers on what outbound path to take
c. To give a hint to the external BGP peers on what inbound path to take
d. To give a hint to local BGP peers on what inbound path to take

Answer: c
Multi-Exit Discriminator (MED) is used when an AS has multiple connections to another AS. It is an attempt by an AS to influence the selected route a neighboring AS should select.

3 Which of the following best describes the BGP weight attribute?

a. Determines a path; not locally significant.
b. Determines a path; lowest value is preferred.
c. Locally significant; lowest value is preferred.
d. Locally significant; highest value is preferred.

Answer: d
The Weight attribute selects a best outbound route, it is not advertised to peers, and it is locally significant. The highest Weight is selected.

4 What is the process by which BGP speakers in a transit AS do not advertise a route until all routers have learned about the route through an IGP?

a. Redistribution
b. BGP synchronization
c. OSPF redistribution
d. OSPF synchronization

Answer: b
BGP synchronization requires that BGP speakers in a transit AS not advertise routes until all routers within that AS have learned about the route through an IGP.

5 What does the number represent in the following router command?
router bgp 200

a. ASN.
b. Process ID.
c. Autonomous process ID.
d. The number is incorrect; it must be 65,000 or higher.

Answer: a
The number is the autonomous system number.

6 Which service access point does BGP use?

a. UDP port 179
b. IP protocol 179
c. TCP port 179
d. None of the above

Answer: c
BGP uses TCP port 179.

7 Which of the following shows the correct order that BGP uses to select a best path?

a. Origin, lowest IP, AS Path, Weight, Local Preference
b. Weight, Local Preference, AS Path, Origin, MED, lowest IP
c. Lowest IP, AS Path, Origin, Weight, MED, Local Preference
d. Weight, Origin, Local Preference, AS Path, MED, lowest IP

Answer: b
Only answer b has the correct order of BGP path selection.

8 BGP communities apply common policy to what?

a. Routers
b. A group of destinations
c. Dampened routes
d. Autonomous systems

Answer: b
BGP communities apply a common policy or properties to a group of destinations.

9 What does the > symbol mean in the output of show ip bgp?

a. Compares a route as less than another
b. Indicates an internal BGP route
c. Compares a route as greater than another
d. Indicates the selected route

Answer: d
The selected route is marked with the > symbol.

10 Which of the following is the administrative distance of an external BGP route?

a. 1
b. 20
c. 50
d. 200

Answer: b
External BGP routes have an administrative distance of 20. Internal BGP routes have an administrative distance of 200.

11 Which mechanism penalizes flapping BGP routes by suppressing them?

a. Route reflectors
b. Route dampening
c. Route suppression
d. Route filtering

Answer: b
Route dampening suppresses flapping BGP routes.

12 Which feature was implemented in BGPv4 to provide forwarding of packets based on IP prefixes?

a. MED
b. VLSM
c. CIDR
d. AS path

Answer: c
Classless Interdomain routing (CIDR) was first implemented in BGPv4.

13 What is configured if an external BGP neighbor does not share a common subnet?

a. BGP confederation, with iBGP only
b. BGP multihop, with eBGP only
c. BGP multihop, with iBGP only
d. BGP confederation, with eBGP only

Answer: b
BGP Multihop is configured to peer with an external BGP neighbor that is not in a local subnet.

14 Which of the following is the best definition of an autonomous system?

a. Group of routers running iBGP
b. Group of routers running OSPF
c. Group of routers running eBGP
d. Group of routers under single administration

Answer: d

15 Which mechanism applies the same policies to a group of neighbors?

a. Peer group
b. Confederation group
c. Community group
d. Route-reflector group

Answer: a
BGP peer groups apply a common set of policies to a group of BGP neighbors.

16 Router A and Router B are in AS 50. Router A has two BGP peers (Router C and Router D) to AS 100. Routers C and D announce the same destination. Router C announces a MED of 200. Router D announces a MED of 300. Which path does Router A take to reach AS 100?

a. Router A
b. Router B
c. Router C
d. Router D

Answer: c
The lowest BGP MED is selected.

17 Router A has three BGP peers: Router B, Router C, and Router D. Routers B, C, and D announce the same destinations. Router B announces the default local preference. Router C announces a local preference of 200. Router D announces a local preference of 300.
Which path does Router A take?

a. Router A
b. Router B
c. Router C
d. Router D

Answer: d
The highest local preference is selected, Router D. The default local preference is 100, which is announced by Router B.

18 Which network prefix is more specific?

a. 100.1.0.0/16
b. 100.1.1.0/24
c. 100.1.0.0/28
d. 100.1.1.0/26

Answer: c
The highest bit mask is more specific.

19 Which command resets all BGP connections?

a. reset ip bgp *
b. show ip bgp *
c. clear ip bgp *
d. disc ip bgp *

Answer: c
The clear ip bgp * command resets all BGP connections.

20 Which of the following BGP routes is selected?

a. AS path = 23 50 801, MED = 10, routerID = 1.1.1.1
b. AS path = 24 51 801, MED = 0, routerID = 2.2.2.2
c. AS path = 100 24 51 801, MED = 10, routerID = 3.3.3.3
d. AS path = 23 50 801, MED = 0, routerID = 4.4.4.4

Answer: b
Following the BGP decision process, check AS Path length, then lowest MED, and then lowest Router ID IP address. Answers b and d both have the same AS Path length and a MED of 0. Because 2.2.2.2 is lower than 4.4.4.4, answer b is selected.

21 BGP has two routes for a network. One has an origin code of i; the second has an origin code of e. Which one is chosen?

a. The route marked with i as the origin type.
b. The route marked with e as the origin type.
c. The route is invalid.
d. Not enough information given.

Answer: a
Based on origin type, routes originated by an IGP (i) are preferred over routes originated by an EGP (e).

22 How many route reflectors are allowed in a cluster?

a. Only one.
b. More than one.
c. Route reflectors are used in confederations.
d. None.

Answer: b
One or more route reflectors are allowed in a cluster.

23 A router announces several networks through redistribution in BGP. If you use the aggregate-address 100.64.0.0 255.252.0.0 command, which networks are announced? Announced networks: 100.64.224.0/24 through 100.65.10.0/24

a. Network 100.64.0.0/14 only
b. Network 100.64.0.0/16 only
c. Network 100.64.0.0/14 and announced networks
d. Network 100.64.0.0/16 and announced networks

Answer: c
Because the summary-only keyword was not in the command, all announced networks are announced with the aggregate network.

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