Review Questions
1 What is the most important difference between BGP-4 and earlier versions of BGP?
2 What two problems was CIDR developed to alleviate?
3 What is the difference between classful and classless IP routers?
4 What is the difference between classful and classless IP routing protocols?
5 Given the addresses 172.17.208.0/23, 172.17.210.0/23, 172.17.212.0/23, and
172.17.214.0/23, summarize the addresses with a single aggregate, using the longest possible address mask.
6 What is an address prefix?
7 The routing table in Example 2-16 is taken from a classless router. To what next-hop address does the router forward packets with each of the following destination addresses?
172.21.255.254
172.16.50.50
172.16.0.224
172.16.51.50
172.17.40.1
172.17.41.1
172.30.1.1
16 'The Routing Table for Review Question 7 Stratford#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, 0 - 0SPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is not set
172.20.0.0 is variably subnetted, 6 subnets, 2 masks D 172.20.0.0 255.255.0.0 [90/409600] via 172.20.5.2, 00:01:50, Ethernet©
D 172.20.2.0 255.255.255.0
[90/409600] via 172.20.6.2, 00:01:50, Ethernetl D 172.20.3.0 255.255.255.0
[90/5401600] via 172.20.6.2, 00:01:50, Ethernetl C 172.20.5.0 255.255.255.0 is directly connected, Ethernet©
C 172.20.6.0 255.255.255.0 is directly connected, Ethernetl
C 172.20.7.0 255.255.255.0 is directly connected, Ethernet2
172.16.0.0 is variably subnetted, 3 subnets, 2 masks D 172.16.50.0 255.255.255.0
[90/409600] via 172.20.6.2, 00:01:50, Ethernetl D 172.16.0.0 255.255.255.0
[90/460800] via 172.20.6.2, 00:01:51, Ethernetl D 172.16.0.0 255.255.0.0 [90/409600] via 172.20.7.2, 00:01:51, Ethernet2
172.17.0.0 is subnetted (mask is 255.255.255.0), 1 subnets D 172.17.40.0 [90/2841600] via 172.20.7.2, 00:01:52, Ethernet2
D 172.16.0.0 (mask is 255.240.0.0) [90/409600] via 172.20.5.2, 00:01:52, Ethernet©
Stratford#
8 Explain how summarization helps hide network instabilities.
9 Explain how summarization can cause asymmetric traffic patterns.
10 Is asymmetric traffic undesirable?
11 What is a NAP?
12 What is a route server?
13 What is a provider-independent address space, and why can it be advantageous to have one?
14 Why can it be a problem to have a /21 provider-independent address space?
15 What is a routing policy?
16 What is the underlying protocol that BGP uses to reliably connect to its neighbors?
17 What are the four BGP message types, and how is each one used?
18 In what state or states can BGP peers exchange Update messages?
19 What is NLRI?
20 What is a path attribute?
21 What are the four categories of BGP path attributes?
22 What is the purpose of the AS_PATH attribute?
23 What are the different types of AS_PATH?
24 What is the purpose of the NEXT_HOP attribute?
25 What is the purpose of the LOCAL_PREF attribute?
26 What is the purpose of the MULTI_EXITJDISC attribute?
27 What attribute or attributes are useful if a BGP speaker originates an aggregate route7
28 What is a BGP administrative weight?
29 Given an EBGP route and an IBGP route to the same destination, which route will a BGP router prefer?
30 A router has two IBGP routes to the same destination. Path A has a LOCAL_PREF of 300 and three AS numbers in the AS JPATH. Path B has a LOCAL_PREF of 200 and two AS numbers in the AS_PATH. Assuming no other differences, which path will the router choose?
31 What is route dampening?
32 Define the penalty, suppress limit, reuse limit, and half-life as they apply to route dampening.
33 What is IGP synchronization, and why is it important?
34 Under what circumstances can you safely disable IGP synchronization?
35 What is a BGP peer group?
36 What is a BGP community?
37 What is a route reflector? What is a route reflection client? What is a route reflection cluster?
38 What is the purpose of the ORIGINATORJD and the CLUSTER_LIST path attributes?
39 What is a BGP confederation?
40 Can route reflectors be used within confederations?
41 What is the purpose of the next-hop-self function? Are there any reasonable alternatives to using this function?
This chapter covers the following key topics:
• Basic BGP Configuration—This section provides a series of case studies for BGP configuration, including peering BGP routers, injecting IBGP routes into BGP, injecting BGP routes into an IGP, IBGP without an IGP, IBGP over an IGP, EBGP multihop, and aggregate routes.
• Managing BGP Connections—This section examines a variety of commands and tools that are available for making BGP connections more manageable from both an administrative and a maintenance standpoint.
• Routing Policies—This section discusses resetting BGP connections and provides a series of case studies covering filtering routes by network layer reachability information (NLRI), by AS_PATH, and with route maps; administrative weight; administering distances and backdoor routes; using the LOCALJPREF and MULTI_EXIT_DISC attributes; prepending the AS_PATH; route tagging; and route dampening.
• Large-Scale BGP—This section provides a series of case studies for large-scale BGP design, including BGP peer groups, BGP communities, private AS numbers, BGP confederations, and route reflectors.
Chapter
Continue reading here: Case Study Peering BGP Routers
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