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Do I Know This Already Quiz

Table 13-1 outlines the major headings in this chapter and the corresponding "Do I Know This Already?" quiz questions.

Table 13-1 "Do I Know This Already?" Foundation Topics Section-to-Question Mapping

Foundation Topics Section	Questions Covered in This Section	Score
Route Filtering and Route Summarization	1-4
BGP Path Attributes and the BGP Decision Process	5-7
Configuring BGP Policies	8-12
BGP Communities	13-14
Total Score

In order to best use this pre-chapter assessment, remember to score yourself strictly. You can find the answers in Appendix A, "Answers to the 'Do I Know This Already?' Quizzes."

1. A BGP policy needs to be configured to filter all the /20 prefixes whose first two octets are 20.128. Which of the following answers would provide the correct matching logic for the filtering process, matching only the described subnets, and no others?

a. access-list 1 deny 20.128.0.0 0.0.255.255

b. access-list 101 deny ip 20.128.0.0 0.0.255.255 host 255.255.240.0

c. ip prefix-list 1 deny 20.128.0.0/16 eq 20

d. ip prefix-list 2 deny 20.128.0.0/16 ge 20 le 20

2. Router R1 has a working BGP implementation, advertising subnets of 1.0.0.0/8 to neighbor 2.2.2.2 (R2). A route map named fred has been configured on R1 to filter all routes in network 1.0.0.0. R1 has just added the router bgp subcommand neighbor 2.2.2.2 route-map fred out. No other commands have been used afterward. Which of the following answers, taken as the next step, would allow proper verification of whether the filter indeed filtered the routes?

a. The show ip bgp neighbor 2.2.2.2 advertised-routes command on R1 will no longer list the filtered routes.

b. The show ip bgp neighbor 2.2.2.2 advertised-routes command on R1 will reflect the filtered routes by listing them with a code of r, meaning "RIB failure."

c. The filtering will not occur, and cannot be verified, until R1 issues a clear ip bgp 2.2.2.2 command.

d. None of the show ip bgp command options on R1 will confirm whether the filtering has occurred.

3. A router needs to match routes with AS_PATHs that include 333, as long as it is not the first ASN in the AS_PATH, while not matching AS_PATHs that include 33333. Which of the following syntactically correct commands could be a part of the complete configuration to match the correct AS_PATHs?

4. R1 and R2 are working BGP peers. The following output of the show ip bgp command shows the entries learned by R1 from R2. It also shows some configuration that was added later on R1. After the appropriate clear command is used to make the new configuration take effect, which of the following entries should R1 have in its BGP table?

e. None of the listed prefixes

5. Which of the following is true regarding BGP path attribute types?

a. The BGP features using well-known attributes must be included in every BGP Update.

b. Optional attributes do not have to be implemented by the programmers that are creating a particular BGP implementation.

c. Nontransitive attributes cannot be advertised into another AS.

d. Discretionary attributes contain sensitive information; Updates should be encoded with MD5 for privacy.

6. Which of the following items in the BGP decision tree occur after the check of the AS_PATH length?

a. Best ORIGIN code b. LOCAL_PREF

d. Whether the next hop is reachable

Network Next Hop Metric

*>i11.10.0.0/16 2.2.2.2 4294967294 *>i11.11.0.0/16 2.2.2.2 4294967294 *>i11.12.0.0/16 2.2.2.2 4294967294 ! New config shown next router bgp 1

neighbor 2.2.2.2 distribute-list 1 in access-list 1 permit 11.8.0.0 0.3.255.255

Network

LocPrf Weight Path

100 0 4 1 33333 10 200 44 i

100 0 4 1 33333 10 200 44 i

7. Which of the following steps in the BGP decision process consider a larger value to be the better value?

a. ORIGIN

b. LOCAL_PREF

c. WEIGHT

e. IGP metric to reach the next hop

8. Which of the following is not advertised to BGP neighbors at all?

a. WEIGHT

c. LOCAL_PREF

d. ORIGIN

9. The following shows the output of the show ip bgp command on R1. Which BGP decision tree step determined which route was best? (Assume that the next hop IP address is reachable.)

Network	Next Hop	Metric	LocPrf	Weight	Path
*> 11.10.	0.0/16 10.1.2.3	4294967294	100	0	4	1	33333 10	200 44	i
* i	2.2.2.2	4294967294	100	0	4	1	33333 1	200 44	i
* i	2.2.2.2	4294967294	100	0	4	1	404 505	303 202	i

a. Largest Weight b. Best ORIGIN code c. Lowest MED

d. Largest LOCAL_PREF

e. Better neighbor type f. None of the answers is correct.

10. The following shows the output of the show ip bgp command on R1. Which BGP decision tree step determined which route was best? (Assume that the NEXT_HOP IP address is reachable.)

Network	Next Hop	Metric	LocPrf	Weight	Path
* 11.10.	0.0/16 10.1.2.3	3	120	10	4 1 33333 10 200 44	?
*>i	2.2.2.2	1	130	30	4 33333 10 200 44 i
* i	2.2.2.2	2	110	20	4 1 404 505 303 202	b. Best ORIGIN code. c. Lowest MED. d. Largest LOCAL_PREF. e. Better Neighbor Type. f. None of the answers is correct. 11. The following exhibit lists commands that were typed using a text editor and later pasted into config mode on router R1. At the time, R1 had a working eBGP connection to several peers, including 3.3.3.3. R1 had learned of several subnets of networks 11.0.0.0/8 and 12.0.0.0/8 via neighbors besides 3.3.3.3. Once pasted, a clear command was issued to pick up the changes. Which of the following statements is true regarding the AS_PATH of the routes advertised by R1 to 3.3.3.3? router bgp 1 neighbor 3.3.3.3 route-map zzz out ip prefix-list matchll seq 5 permit 11.0.0.0/8 le 32 route-map zzz permit 10 match ip address prefix-list match11 set as-path prepend 1 1 1 a. No changes would occur, because the configuration would be rejected due to syntax errors. b. Routes to subnets inside network 11.0.0.0/8 would contain three consecutive 1s, but no more, in the AS_PATH. c. Routes to subnets inside 11.0.0.0/8 would contain at least four consecutive 1s in the AS_PATH. d. Routes to subnets inside 12.0.0.0/8 would have no 1s in the AS_PATH. e. Routes to subnets inside 12.0.0.0/8 would have one additional 1 in the AS PATH. 12. Which of the following must occur or be configured in order for BGP to mark multiple iBGP routes in the BGP table—entries for the exact same destination prefix/length—as the best routes? a. Inclusion of the maximum-paths number command under router BGP, with a setting larger than 1. b. Inclusion of the maximum-paths ibgp number command under router BGP, with a setting larger than 1. c. Multiple routes that tie for all BGP decision process comparisons up through checking a route's ORIGIN code. d. BGP cannot consider multiple routes in the BGP table for the exact same prefix as best routes. 13. Which of the following special BGP COMMUNITY values, when set, imply that a route should not be forwarded outside a confederation AS? a. LOCAL_AS b. NO_ADVERT c. NO_EXPORT d. NO_EXPORT_SUBCONFED 14. When BGP peers have set and sent COMMUNITY values in BGP Updates, which of the following is true? a. The BGP decision process adds a check for the COMMUNITY just before the check for the shortest AS_PATH length. b. The lowest COMMUNITY value is considered best by the BGP decision process, unless the COMMUNITY is set to one of the special reserved values. c. The COMMUNITY does not impact the BGP decision process directly. d. None of the other answers is correct.

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