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Review Questions

Answer the following questions, and then see Appendix A, “Answers to Review Questions,” for the answers.

1.What is the difference between an IGP and an EGP?
2.What type of routing protocol is BGP?
3.Select the true statements.
  1. In a Layer 2 MPLS VPN, all the customer edge routers are on the same IP subnet.

  2. In a Layer 3 MPLS VPN, all the customer edge routers are on the same IP subnet.

  3. In a Layer 2 MPLS VPN, each customer edge router is on a different IP subnet.

  4. In a Layer 3 MPLS VPN, each customer edge router is on a different IP subnet.

4.What is the difference between BGP dual homing and dual multihoming?
5.What are three common design options for BGP multihoming?
6.What are some advantages of getting default routes and selected specific routes from your ISPs?
7.What is a disadvantage of having all ISPs pass all BGP routes into your autonomous system?
8.A BGP router knows of three paths to a network and has chosen the best path. Can this BGP router advertise to its peer routers a route to that network other than the best path?
9.When is it appropriate to use BGP to connect to other autonomous systems?
10.When is it appropriate to use static routes rather than BGP to interconnect autonomous systems?
11.What protocol does BGP use as its transport protocol? What port number does BGP use?
12.How does BGP guarantee a loop-free autonomous system path?
13.Any two routers that have formed a BGP connection can be referred to by what two terms?
14.Write a brief definition for each of the following:



Well-known attribute

Transitive attribute

BGP synchronization

15.What tables are used by BGP?
16.What are the four BGP message types?
17.How is the BGP router ID selected?
18.What are the BGP states a router can be in with its neighbors?
19.What type of BGP attributes are the following?




Local preference

Atomic aggregate




20.When IBGP advertises a prefix that was originally learned via EBGP, by default what does it use for the next-hop attribute of the update?
21.Describe the complication that an NBMA network can cause for an update’s next-hop attribute.
22.Complete the following table to answer these questions about three BGP attributes:
  • In which order are the attributes preferred (1, 2, or 3)?

  • For the attribute, is the highest or lowest value preferred?

  • Which other routers, if any, is the attribute sent to?

AttributeOrder Preferred InHighest or Lowest Value Preferred?Sent to Which Other Routers?
Local preference   

23.Under what circumstances should BGP synchronization be disabled?
24.What does the neighbor ebgp-multihop command do?
25.Which commands are used to configure Routers A and B if Router A is to run BGP in autonomous system 65000 and establish a neighbor relationship with Router B in autonomous system 65001? The two routers are directly connected but should use their loopback 0 addresses to establish the BGP connection; Router A has loopback 0 address, and Router B has loopback 0 address
26.What command disables BGP synchronization if it is enabled?
27.Which command would Router A in autonomous system 65000 use to activate an IBGP session with Router B,, also in autonomous system 65000?
28.What is the difference between the BGP neighbor command and the BGP network command?
29.Your router’s routing table has a route for You configure the network mask command for the BGP process running on the router. What does this command do?
30.What does the clear ip bgp soft out command do?
31.Which command is used to display detailed information about BGP connections to neighbors?
32.What does a > in the output of the show ip bgp command mean?
33.What column in the show ip bgp command output displays the MED?
34.How is the established neighbor state represented in the output of the show ip bgp summary command?
35.What type of authentication does BGP support?
36.How can BGP path manipulation affect the relative bandwidth used between two connections to the Internet?
37.Describe what the following configuration on Router A does:
route-map local_pref permit 10
 match ip address 65
 set local-preference 300
route-map local_pref permit 20
router bgp 65001
 neighbor remote-as 65002
 neighbor route-map local_pref in

38.Place the BGP route-selection criteria in order from the first step to the last step evaluated by placing a number in the blank provided.

____ Prefer the path with the lowest neighbor BGP router ID

____ Prefer the lowest MED

____ Prefer the shortest AS-path

____ Prefer the oldest route for EBGP paths

____ Prefer the lowest origin code

____ Prefer the highest weight

____ Prefer the path through the closest IGP neighbor

____ Prefer the highest local preference

____ Prefer the route originated by the local router

____ Prefer the route with the lowest neighbor IP address

____ Prefer the EBGP path over the IBGP path

39.What command is used to assign a weight to updates from a BGP neighbor connection?
40.What does the ip as-path access-list command do?
41.Describe what AS-path prepending is.
42.What effect would the ip prefix-list test permit ge 8 le 20 command have on the route and on the route?


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