13. Each line in the diagram represents a single connection from a user AS to an ISP AS. In which multihomed configuration is it necessary, if not required, to use BGP to exchange routing information?
- A
- B
- C
- D
Explanation: BGP should be used when multihomed or connected to multiple autonomous systems.
14. Which three options are well-known BGP community sets? (Choose three.)
- Internet
- Test_Only
- No_Export
- No_Transit
- Transit_Only
- No_Advertise
Explanation: Three common well-known communities are as follows:
- Internet: This is a standardized community for identifying routes that should be advertised on the Internet.
- No_Advertise: Routes with this community should not be advertised to any BGP peer (IBGP or EBGP).
- No_Export: When a route with this community is received, the route is not advertised to any EBGP peer. Routes with this community can be advertised to IBGP peers.
15. A network administrator is configuring a prefix list with the command
ipv6 prefix-list IPV6-1 seq 5 permit 2001:db8:abcd:20::/59 ge 62
Which network matches the prefix match specification?
- 2001:db8:ab:20::/62
- 2001:db8:abcd:2::/59
- 2001:db8:abcd:36::/62
- 2001:db8:abcd:60::/64
Explanation: The prefix matching logic works exactly the same for IPv6 networks as for IPv4 networks. The third hexadecimal group of the match specification is 0x0020, which is 00000000 00100000 in binary. To match /59 prefix length, the third hexadecimal group of a network must match 00000000 001, that is, between 0x0020 and 0x003F. The prefix length must be /62 or higher.
“Do I Know This Already?” Quiz Answers:
1. Transit routing between a multihomed enterprise network and a service provider is generally not recommend in which scenarios? (Choose all that apply.)
- Internet connections at data centers
- Internet connections at branch locations
- MPLS data centers
- MPLS branch locations
Explanation: Transit routing for enterprises is generally acceptable only for data centers connecting to MPLS networks.
2. True or false: An extended ACL used to match routes changes behavior if the routing protocol is an IGP rather than BGP.
- True
- False
Explanation: IGPs use the destination field to select the smallest prefix length, whereas BGP uses it to match the subnet mask for a route.
3. Which network prefixes match the prefix match pattern 10.168.0.0/13 ge 24? (Choose two.)
- 10.168.0.0/13
- 10.168.0.0/24
- 10.173.1.0/28
- 10.104.0.0/24
Explanation:
Basic Prefix Match Pattern
4. What is the correct regular expression syntax for matching a route that originated in AS 300?
- ^300_
- $300!
- _300_
- _300$
Explanation:
| Regular Expression | Meaning |
|---|---|
| ^$ | Local originating routes |
| permit ^200_ | Only routes from neighbor AS 200 |
| permit _200$ | Only routes originating from AS 200 |
| permit _200_ | Only routes that pass through AS 200 |
| permit ^[0-9]+ [0-9]+ [0-9]+? | Routes with three or fewer AS_Path entries |
5. What happens when the route map route-map QUESTION permit 20 does not contain a conditional match statement?
- The routes are discarded, and a syslog message is logged.
- All routes are discarded.
- All routes are accepted.
- An error is assigned when linking the route map to a BGP peer.
Explanation: All routes are accepted and processed.
6. What happens to a route that does not match the PrefixRFC1918 prefix list when using the following route map?
route-map QUESTION deny 10 match ip address prefix-list PrefixRFC1918 route-map QUESTION permit 20 set metric 200
- The route is allowed, and the metric is set to 200.
- The route is denied.
- The route is allowed.
- The route is allowed, and the default metric is set to 100.
Explanation: Because the route does not match the prefix list, sequence 10 does not apply, and the route moves on to sequence 20 which sets the metric to 200. It is implied that the route proceeds because it was modified.
7. True or false: A BGP AS_Path ACL and a prefix list can be applied to a neighbor at the same time.
- True
- False
Explanation: A distribute list and a prefix list cannot be used at the same time for a neighbor. All other filtering techniques can be combined.
8. Which of the following is not a well-known BGP community?
- No_Advertise
- Internet
- No_Export
- Private_Route
Explanation: The other communities are common global communities.
9. Which of the following techniques is the second selection criterion for the BGP best path?
- Weight
- Local preference
- Origin
- MED
Explanation: Local preference is the second selection criterion for the BGP best path.
10. True or false: For MED to be used as a selection criterion, the routes must come from different autonomous systems.
- True
- False
Explanation: For MED to be used, the routes must come from the same AS.