CCNP Route FAQ: Internet Connectivity and BGP

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by James Palmer
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8 months ago

CCNP Route FAQ: Internet Connectivity and BGP

Q1. Which of the following are considered private IPv4 addresses? (Choose two.)
a. 192.16.1.1
b. 172.35.1.1
c. 225.0.0.1
d. 127.0.0.1
e. 10.1.1.1

Answer: B and E. The private IPv4 address space consists of Class A network 10.0.0.0, Class B networks 172.16.0.0–172.31.0.0, and the 256 Class C networks that begin 192.168.


Figure: Conceptual View of Public IPv4 Address Assignment

Q2. Class C network 200.1.1.0/24 was allocated to an ISP that operated primarily in Asia. That ISP then assigned this entire Class C network to one of its Asian customers. Network 200.1.2.0/24 has yet to be assigned to any ISP. Which of the following is most likely to be true?
a. 200.1.2.0/24 could be assigned to any registrar or ISP in the world.
b. 200.1.2.0/24 will be assigned in the same geography (Asia) as 200.1.1.0/24.
c. 200.1.2.0/24 cannot be assigned as public address space.
d. Routers inside North American ISPs increase their routing table size by 1 as a result of the customer with 200.1.1.0/24 connecting to the Internet.

Answer: B. ICANN and IANA manage the assignment of public IPv4 address space such that large address blocks (often called CIDR blocks) exist in a particular geography or are assigned to particular ISPs. As such, Internet routers can more easily create summary routes to help keep the routing table small in the Internet. 200.1.2.0/24 would likely also be allocated to some registrar, ISP, or customer in Asia. Because of the large route summaries, in this case possibly a summary for 200.0.0.0/8, routers in North America would not see an increase in the size of their routing tables.

Q3. Router R1, in ASN 11, learns a BGP route from BGP peer R22 in ASN 22. R1 and then uses BGP to advertise the route to R2, also in ASN 11. What ASNs would you see in the BGP table on R2 for this route?
a. 22
b. 11
c. 1
d. None

Answer: A. The router in ASN 22, R22, advertises the BGP update with (at least) 22 in the AS_Path Path Attribute (PA). When R1 advertises the route to R2, also in ASN 11, R1 does not add an ASN. As a result, R2’s AS_Path has at least ASN 22 and not ASN 11.

Q4. Which of the following are most likely to be used as an ASN by a company that has a registered public 16-bit ASN? (Choose two.)
a. 1
b. 65,000
c. 64,000
d. 64,550

Answer: A and C. The public range of 16-bit BGP ASNs is 1 through 64,495.

Q5. Which of the following statements is true about a router’s eBGP peers that is not also true about that same router’s iBGP peers?
a. The eBGP peer neighborship uses TCP.
b. The eBGP peer uses port 180 (default).
c. The eBGP peer uses the same ASN as the local router.
d. The eBGP peer updates its AS_Path PA before sending updates to this router.

Answer: D. The question asks which answers are true about the eBGP peer but also not true about an iBGP peer. Both iBGP and eBGP use TCP port 179. An eBGP peer uses a different ASN than the local router, by definition, making that answer incorrect. The correct answer refers to the fact that an eBGP peer adds its own ASN to the BGP AS_Path PA before sending routing information to another router, whereas iBGP peers do not.

Q6. Which of the following is the primary motivation for using BGP between an Enterprise and its ISPs?
a. To influence the choice of best path (best route) for at least some routes
b. To avoid having to configure static routes
c. To allow redistribution of BGP routes into the IGP routing protocol
d. To monitor the size of the Internet BGP table

Answer: A. Although using BGP does avoid some static configuration at the Enterprise and the ISP, the primary reason to consider using BGP in the Enterprise is to influence and react to Path Attributes for the purpose of choosing the best path. Typically, engineers do not redistribute BGP routes into the IGP due to scalability problems. And although it may be interesting to monitor the size of the Internet BGP table, it is not a primary motivation for choosing to use BGP on a router.

Q7. The following terms describe various design options for Enterprise connectivity to the Internet. Which of the following imply that the Enterprise connects to two or more ISPs? (Choose two.)
a. Single Homed
b. Dual Homed
c. Single Multihomed
d. Dual Multihomed

Answer: C and D. The terms “homed” makes reference to a single homed ISP, and “multihomed” to multiple ISPs. The terms “single” and “dual” refer to the number of connections to each ISP.

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