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BGP Fundamentals 2

Here you will find answers to BGP Fundamentals – Part 2

Question 1

In a multihomed environment with two ISP connections, which two statements are true? (Choose two)

A. The customer should not be configured to act as a transit AS between the two ISPs.
B. It is recommended that the multi-homed customer use a registered (public) AS number.
C. AS-Path prepending can be configured on the customer’s edge router to influence the BGP path selection process for the outbound traffic (traffic from the customer to the ISPs).
D. The customer can use Local Preference on the customer’s edge routers to influence the BGP path selection process for the inbound traffic (traffic from the ISPs to the customer).
E. The advertisement of the customer’s IP address space can be conditioned by the customer’s edge routers by using a static route to the nullO interface and by using the proper network statement under router bgp

 

Answer: A B

Question 2

Which four attributes are used by BGP to detect routing loops? (Choose four)

A. AS-Path
B. Cluster ID
C. Cluster List
D. Originator ID
E. Community ID

 

Answer: A B C D

Question 3

Which three statements are true about route reflectors? (Choose three)

A. If the route is learned from an EBGP peer by the route reflector, it is reflected to all IBGP and EBGP peers.
B. If the route is learned from a non-client IBGP peer by the route reflector, it is reflected to all EBGP peers only.
C. If the route is learned from a non-client IBGP peer by the route reflector, it is reflected to EBGP peers and clients only.
D. If the route is learned from a client IBGP peer by the route reflector, it is reflected to all clients only, except the originating client.
E. If the route is learned from a client IBGP peer by the route reflector, it is reflected to all EBGP peers, non-clients, and clients (except the originating client).

 

Answer: A C E

Question 4

Based on the following show ip bgp neighbors 2.2.2.2 output, which two statements are true? (Choose two)

R1#show ip bgp neighbors 2.2.2.2
BGP neighbor is 2.2.2.2, remote AS 102, internal link
Index 1, Offset 0, Mask 0x2
BGP version 4, remote router ID 66.0.0.1
BGP state=Established, table version=1, up for 00:14:52
Last read 00:00:52, hold time is 180, keepalive interval is 60 seconds
Minimum time between advertisement runs is 5 seconds
Received 233 messages, 0 notifications, 0 in queue
Sent 206 messages, 0 notifications, 0 in queue
Prefix advertised 0, suppressed 0, withdrawn 0
Connections established 17; dropped 16
Last reset 00:15:02, due to User reset
18 accepted prefixes consume 576 bytes, maximum limit 20
Threshold for warning message 80%
0 history paths consume 0 bytes

A. R1 has accepted 20 prefixes from the 2.2.2.2 IBGP neighbor.
B. R1 generated a warning message to the router’s console after the 2.2.2.2 IBGP neighbor sent 16 prefixes to R1.
C. R1 generated a warning message to the router’s console after the 2.2.2.2 IBGP neighbor sent 15 prefixes to R1.
D. R1 will drop its neighbor relationship to the 2.2.2.2 IBGP neighbor if 2.2.2.2 sends two more additional prefixes to R1.
E. R1 will drop its neighbor relationship to the 2.2.2.2 IBGP neighbor if 2.2.2.2 sends three more additional prefixes to R1.

 

Answer: B E

Question 5

During the autonomous system number migration process, which BGP feature allows a BGP router to act as a router within one autonomous system to some BGP neighbors but also appear to be in another autonomous system to other neighbors?

A. remove-private-as
B. local-as
C. as-path prepending
D. AS override
E. Site-of-Origin (Soo)

 

Answer: B

Question 6

Based on this configuration, which two peering router neighbor statements are correct? (Choose two)

router bgp 50001
neighbor 192.168.1.1 remote-as 50001
neighbor 10.1.1.1 remote-as 50002
neighbor 10.1.1.1 local-as 50003
!
output omitted

A. EBGP – neighbor 10.1.1.2 remote-as 50003
B. EBGP – neighbor 10.1.1.2 remote-as 50001
C. EBGP – neighbor 10.1.1.2 remote-as 50001 and neighbor 10.1.1.2 local-as 50003
D. IBGP – neighbor 192.168.1.2 remote-as 50001
E. IBGP – neighbor 192.168.1.2 remote-as 50003
F. IBGP – neighbor 192.168.1.2 remote-as 50003 and neighbor 192.168.1.2 local-as 50001

 

Answer: A D

Question 7

Which command is used to advertise a summary route while suppressing only a subset of the more specific routes?

A. network {ip prefix} {mask}
B. network {ip prefix} {mask} unsuppress-map {route-map-name}
C. aggregate-address {ip prefix} {mask}
D. aggregate-address {ip prefix} {mask} summary-only
E. aggregate-address {ip prefix} {mask} suppress-map {route-map-name}
F. aggregate-address {ip prefix} {mask} as-set summary-only

 

Answer: E

Question 8

What is the correct command to set the BGP scanner interval to two minutes?

A. bgp scan-time 2
B. bgp scan-time 120
C. bgp scan-time 2 60
D. The maximum scanning interval cannot exceed one minute

 

Answer: D

Question 9

Given the AS-path of (51002 51003) 51001 i from the show ip bgp output, what is the origin?

A. AS 51001
B. AS 51002
C. AS 51003
D. (51002 51003)
E. IGP
F. IBGP

 

Answer: E

Question 10

AS-PATH prepending is used in AS1 in order to influence the return traffic path from AS 5 to AS 1 through the higher speed path via AS 2. ______ needs to be configured for AS-Path prepending and a minimum of ______ of the AS number should be prepended.

AS_PATH.jpg

A. R1; one copy
B. R2; one copy
C. R1; two copies
D. R2; two copied
E. R2; three copies

Answer: C

Question 11

Which two configuration commands will complete the BGP configuration on R1 so it will conditionally announce the 172.0.0.0/8 prefix to R4 via BGP? (Choose two)

BGP_prefix.jpg

hostname R1
!
output omitted
!
1. ______________________
!
router bgp 65001
neighbor 172.16.1.1 remote-as 65001
neighbor 2.2.2.2 remote-as 65001
neighbor 4.4.4.4 remote-as 387
!
2. ______________________

A. 2. network 172.16.0.0
auto-summary
B. 2. network 172.0.0.0 mask 255.0.0.0
C. 1. ip route 172.0.0.0 255.0.0.0 null0
D. 1. ip route 172.0.0.0 255.0.0.0 null0 255
E. 1. ip route 172.0.0.0 255.0.0.0 172.16.1.1
F. 2. aggregate-address 172.0.0.0 mask 255.0.0.0

 

Answer: B E

Question 12

R2 is configured to prepend AS number 65102 in updates to R3. Which statement is true?

BGP_AS_Prepend.jpg

A. The BGP updates from R2 to R3 will be rejected by R3 due to loop prevention.
B. The EBGP session between R2 and R3 will be dropped due to an AS-Path prepend configuration error.
C. The AS-Path length via AS 65102 will increase to influence the return traffic path selected by the remote ASs.
D. The AS-Path length via AS 65102 will decrease to influence the return traffic path selected by the remote ASs.
E. The AS-Path prepend configuration command using the remote AS number (65102) will be rejected by IOS at R2.

 

Answer: A

Question 13

Refer to the partial topology diagram shown.

BGP_source_update.jpg

Service Provider 1 (SP1) assigned the customer an AS number of 65275.
Service Provider 2 (SP2) assigned an AS number of 65745 to the customer.
The customer decides to use AS 65275 internally.
Which of the following is the correct partial router configuration to cause updates from CR1 to SP1 to report a source AS of 65275, while updates from CR2 to SP2 report the source AS of 65745 in addition to AS 65275?

A.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65275
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

B.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65745
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

C.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 1.1.1.1 local-as 65745
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65275
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65745
neighbor 10.1.1.1 remote-as 65275

D.
!
CR1
router bgp 65275
neighbor 1.1.1.1 remote-as 65274
neighbor 10.1.1.2 remote-as 65275

CR2
router bgp 65745
neighbor 2.2.2.2 remote-as 65732
neighbor 2.2.2.2 local-as 65275
neighbor 10.1.1.1 remote-as 65275

 

Answer: A

Question 14

In the diagram, the customer is using static routing to connect to the ISP. Which configuration on the ISP edge routers will enable load balancing and backup of the traffic to the customer?

BGP_ISP_edge_router.jpg

A.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0

B.
R1
ip route 10.1.1.0 255.255.255.0 serial 0
R2
ip route 10.1.1.128 255.255.255.0 serial0

C.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
ip route 10.1.1.128 255.255.255.128 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.128 serial 0

D.
R1
ip route 10.1.1.0 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.0 serial 0
R2
ip route 10.1.1.128 255.255.255.128 serial 0
ip route 10.1.1.0 255.255.255.0 serial 0

 

Answer: D

Question 15

An OSPF LSA type 1 route is redistributed into MP-BGP. That same route is then redistributed back from MP-BGP into OSPF on another PE router. In this case, which LSA type on the destination CE router will the OSPF route appear as?

A. LSA type 1
B. LSA type 2
C. LSA type 3
D. LSA type 4
E. LSA type 5
F. LSA type 7

 

Answer: C

Question 16

When using the redistribute ospf {process-id} command, which types of OSPF routes will be redistributed into BGP?

A. all internal (interarea and intra-area) OSPF routes
B. all external OSPF routes
C. all external OSPF routes except type 7 LSAs
D. both internal and external OSPF routes
E. only classful OSPF routes without the subnet option
F. only external OSPF routes without the match option

 

Answer: A

Question 17

What best describes the following configuration example of allowas-in?

router bgp 100
address-family ipv4 vrf CustomerA
neighbor 195.12.4.5 remote-as 123
neighbor 195.12.4.5 activate
neighbor 195.12.4.5 allowas-in 2

A. permits incoming BGP updates defined by access-list 2
B. permits incoming BGP updates defined by class-map 2
C. permit incoming BGP updates defined by route-map 2
D. permits incoming BGP updates with no more than two occurrences of AS 100 in the AS path
E. permits incoming BGP updates with no more than two occurrences of AS 123 in the AS path

 

Answer: D

Question 18

Who should use private AS numbers?

A. multihomed customers who configured their AS as a transit AS
B. customers multihomed to two different ISPs
C. customers multihomed to a single ISP using multiple permanent links
D. customers connected to a single ISP using a single permanent link

 

Answer: C

Question 19

Refer to the outputs shown in the exhibit. What could be preventing the R1 router from receiving any prefixes from the R2 BGP neighbor?

R1#show ip bgp summary
BSP router identifier 199.199.199.199, local AS number 20
BGP table version is 45, main routing table version 45
44 network entries using 4444 bytes of memory
81 path entries using 3888 bytes of memory
13 BGP path attribute entries using 780 bytes of memory
11 BGP AS-PATH entries using 264 bytes of memory
4 BGP route-map cache entries using 64 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 9440 total bytes of memory
BGP activity 88/44 prefixes, 191/110 paths, scan interval 5 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.168.1.17 4 1 1628 2693 45 0 0 00:42:22 31
192.168.20.22 4 22 70 73 45 0 0 00:42:26 31
192.168.31.1 4 65002 172 274 0 0 0 00:00:13 Idle

R1#telnet 192.168.31.1
Trying 192.168.31.1 … Open

User Access Verification

Password: cisco

R2#sh run | begin bgp
router bgp 65002
bgp confederation identifier 1
bgp confederation peers 65001
network 10.0.0.0
neighbor 192.168.31.2 remote-as 20

A. There is a TCP session establishment problem between R1 and R2.
B. The no sync command is missing on R2.
C. The no sync command is missing on R1.
D. R2 is using the wrong AS number in its neighbor 192.168.31.2 remote-as statement.
E. R1 is using the wrong AS number in its neighbor 192.168.31.1 remote-as statement.
F. Both R1 and R2 are not using a loopback address to source their BGP packets.

 

Answer: E

Categories: BGP + MPLS 642-691 Exam Tags:
  1. SC
    April 27th, 2011 at 20:27 | #1

    Dear iptut
    i think that the routers names in the answer’s section doesn’t reflects the names on the diagram topology and after question 12 the question aren’t numbered – it will helpful for the users for asking questions.
    and thanks alot for this helpful site.

  2. iptut
    April 27th, 2011 at 23:50 | #2

    @SC: In fact, this site is under construction and some categories are not well-organized. We will make changes as soon as possible.

    We are sorry for the inconvenience.

  3. NB
    April 30th, 2011 at 11:27 | #3

    Can someone explain the answer of question 19

  4. SC
    May 2nd, 2011 at 19:08 | #4

    @NB
    ANS E is correct because
    from R1 perspective R2 is in AS 65002 (by the AS number – from the Show ip bgp summary table – third line)
    from R2 perspective R1 is in AS 20 (by the command “network 192.168.32.2 remote-as 20”)

    R2 identifies it self to R1 like he is in AS 1 (by the line “bgp confederation identifier 1)
    so R1 should connect to R2 to AS 1 and not as 65002

    hope i was clear enough

  5. NB
    May 4th, 2011 at 09:54 | #5

    @SB thanks

  6. Cheen
    May 5th, 2011 at 03:05 | #6

    Hi Iptut,
    Can you clarify why the answer in question 14 is D?Thanks!

  7. pOp
    May 17th, 2011 at 04:56 | #7

    @Cheen

    Q 14 : Requirements => 1.Load Balancing , 2.Backup

    1.For Load Balancing

    R1
    ip route 10.1.1.0 255.255.255.128 serial 0
    R2
    ip route 10.1.1.128 255.255.255.128 serial 0

    2.For Backup (what if 1 router goes down, so)

    R1
    ip route 10.1.1.0 255.255.255.0 serial 0
    R2
    ip route 10.1.1.0 255.255.255.0 serial 0

  8. @SC
    May 24th, 2011 at 07:54 | #8

    Thanks for the explaining the Q19…

    and Thanks iptut for this wonderful site…and the explanation part is going great ..Thanks

  9. Jack
    June 7th, 2011 at 02:42 | #9

    For the Q10, the diagram didn’t show which router is R1 and R2. We only can imagine either top is R1 or bottom is R1. Based on the answer provided, I assumed bottom is R1 at AS1. What do you think?

  10. Kal
    June 20th, 2011 at 14:18 | #10

    I think you are right 🙂

  11. Kadeesa
    July 18th, 2011 at 19:38 | #11

    @all
    Can someone explain Q.15 to me, please! Thanks!

  12. Alex
    July 24th, 2011 at 09:37 | #12

    Are you sure of answer for Q18?
    what does “multiple permanent links” refer to?

  13. saroj
    November 1st, 2011 at 12:25 | #13

    Which bgp book is best for reference ?? can anyone give me the site location to download… thanks in advance

  14. ccip
    November 22nd, 2011 at 14:02 | #14

    hi can someone send me study material for ccip bgp+mpls 9642-691) to the following email address

    ccipccip4@gmail.com

  15. @ all
    December 1st, 2011 at 14:53 | #15

    How is it that the answer to Q15 is C (summary LSA). In my opinion it should be E (Lsa Type 5 – external Lsa) . does Anyone have a different opinion ?

  16. wagzy
    February 18th, 2012 at 10:39 | #16

    @all. That is what I think too.

    I hope someone can explain why a route imported from bgp process into ospf process should be LSA type 3 (ASBR summary route from one area to another) instead of LSA type 5 (which is information imported into OSPF from other routing processess).

  17. wagzy
    February 18th, 2012 at 11:18 | #17

    @all

    MP-BGP attaches two new extended community attributes to the routes redistributed from OSPF:

    OSPF domain identifier extended community attribute
    OSPF route type extended community attribute

    MP-BGP uses these attributes and the MED to preserve OSPF routing information across the BGP/MPLS VPN backbone

    At the remote PE site, MP-BGP converts the OSPF routes to BGP VPN-IPv4 routes and sends them across the BGP/MPLS VPN backbone. At the destination PE, MP-BGP must redistribute the BGP VPN-IPv4 routes back into OSPF IPv4 routes. The PE OSPF router becomes the originator of the routes, which are either type 5 external routes or type 3 internal routes. The PE can announce the OSPF routes to the appropriate CE router via its directly connected PE-CE OSPF link.

    If the route has a route type of inter or intra, it is redistributed as a type 3 summary interarea route and the destination PE router generates a type 3 LSA for it.

    A route is redistributed as an external route if the route:

    Originates in an OSPF domain that is different from that of the destination PE router.
    Has a route type of 5 or 7, both of which indicate an external route.

    In the first case, the PE advertises the route as an external type 2 route. In the second case, the PE advertises the route as an external type 2 route if the least-significant bit is set in the option byte in the route type extended community attribute; otherwise the PE advertises the route as external type 1 route.

    for more reading, check out

    http://www.juniper.net/techpubs/software/erx/erx41x/swconfig-routing-vol2/html/bgp-mpls-vpns-config5.html

  18. MB
    April 7th, 2012 at 12:22 | #18

    Can Anyone explain Question 10???

  19. ki
    May 15th, 2012 at 17:35 | #19

    Dear @MB, the question router labeling is not clear but if the lower router is R1, at least two AS pre-pending is necessary to compare AS-PATH length.

  20. Used Cisco
    June 25th, 2012 at 07:36 | #20

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  21. Shalash
    July 10th, 2012 at 06:50 | #21

    Could any body please explain the answer for Q16

  22. MMNS
    July 11th, 2012 at 15:13 | #22

    Q1) can anyone explained the answer??

  23. Dinesh Kumar
    December 7th, 2012 at 02:14 | #23

    in CCNA there is tutorial available for each topic before taking the questions and answers. but here it was not available if its available better for us to recalling… Since CCNA explanation given was very simple to learn by anyone.. same expecting for each topic in CCNP as well as CCI………..

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    December 27th, 2012 at 14:53 | #24

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