Configuration Exercises

Table 3-4 shows the routers and addresses used for configuration exercises 1 through 13.

Table 3-4 Routers/Addresses for Configuration Exercises 1-13

Autonomous System

Router

Interface

IP Address/Mask

1

R1

LO

10.255.255.1/32

SO

192.168.100.1/30

EO

192.168.100.5/30

El

192.168.100.13/30

R2

LO

10.255.255.2/32

SO

192.168.100.9/30

SI

192.168.100.57/30

EO

192.168.100.6/30

El

192.168.100.17/30

R3

LO

10.255.255.3/32

SO

192.168.100.25/30

EO

192.168.100.18/30

El

192.168.100.21/30

R4

LO

10.255.255.4/32

SO

192.168.100.29/30

SI

192.168.100.33/30

EO

192.168.100.22/30

El

192.168.100.14/30

Table 3-4 Routers/Addresses for Configuration Exercises 1-13 (Continued)

Autonomous System

Router

Interface

IP Address/Mask

2

R5

SO

192.168.100.2 /30

EO

192.168.1.129/26

R6

SO

192.168.100.10/30

EO

192.168.1.130/26

3

R7

LO

10.255.255.7/32

SO

192.168.100.26/30

SI

192.168.100.41/30

EO

192.168.100.37/30

El

172.16.1.1/24

4

R8

LO

10.255.255.8/32

SO

192.168.100.30/30

SI

192.168.100.45/30

EO

192.168.100.38/30

El

172.16.2.1/24

5

R9

LO

10.255.255.9/32

SO

192.168.100.42/30

EO

192.168.9.1/24

El

192.168.150.1/24

RIO

LO

10.255.255.10/32

SO

192.168.100.46/30

EO

192.168.10.1/24

El

192.168.100.53/30

E2

192.168.150.2/24

Rll

LO

10.255.255.11/32

SO

192.168.100.34/30

EO

192.168.100.54/30

El

192.168.11.1/24

6

R12

LO

192.168.255.1/32

SO

192.168.100.58/30

EO

192.168.16.83/27

Table 3-4 lists the autonomous systems, routers, interfaces, and addresses used in configuration exercises 1 through 13. All interfaces of the routers are shown. For each exercise, if the table indicates that the router has a loopback interface, that interface should be the source of all IBGP connections. EBGP connections should always be between physical interface addresses, unless otherwise specified in an exercise. Hint: Draw the internetwork, based on the subnets listed in the table, before attempting the exercises.

1 AS 1 in Table 3-4 is a transit AS, and the IGP is OSPF. Area 0 spans the entire AS. N< > networks internal to the AS are advertised outside of the AS. None of the subnets over which EBGP is run should be advertised into AS 1. Write BGP configurations for the routers in AS 1, putting all internal neighbors in a peer group called LOCAL. For R3 only, EBGP peering should be performed between loopback interfaces. Authenticate all IBGP connections with the password ExeRCisel.

2 AS 2 in Table 3-4 is a stub (nontransit) AS, and its IGP is EIGRP. Configure the routers in AS 2 to speak EBGP to any external peers and to redistribute any EIGRP routes into BGP. Redistribute BGP-learned routes into EIGRP. Implement any necessary filters to prevent incorrect routes from being redistributed.

3 Networks 192.168.1.0, 192.168.2.0, 192.168.3.0, 192.168.4.0, and 192.168.5.0 exisi within AS 2. The administrator of this AS wants the neighboring AS to prefer R5 when sending traffic to 192.168.1.0 and 192.168.3.0. The neighboring AS should prefer R6 when sending traffic to 192.168.2.0 and 192.168.4.0. In each case, the less-preferred link serves as a backup to the more-preferred link. 192.168.5.0 is a private network and must not be advertised to any EBGP peer. Modify the configurations written in Exercise 2 to implement this policy.

4 Configure the EBGP neighbors of R5 and R6 to advertise a default route to AS 2. No other routes are to be advertised.

5 The administrator of AS 2's neighboring AS disagrees with part of the policy set in Exercise 2. He wants all routers in his AS to send traffic destined for 192.168.3.0 to R6, with R5 as a backup. All traffic destined for 192.168.4.0 should be sent to R5, with R6 as a backup. The rest of the policy set in Exercise 2 is acceptable. Write configurations to implement this policy.

6 AS 3 in Table 3-4 is a stub AS, and AS 4 is a transit AS. The IGP of both autonomous systems is OSPF, and the internal interfaces of R7 and R8 are both in area 0. Write BGP and OSPF configurations for R7 and R8, advertise the internal addresses shown in Table 3-4 to all EBGP peers, and ensure that routers in the OSPF domains can reach any external destination. Do not redistribute routes in either direction. Also, ensure that the BGP router ID of R7 is 192.168.3.254.

7 Modify the configurations of Exercise 6 so that R7 and R8 speak OSPF across the link directly connecting them; remove BGP from the link. Traffic between subnets 172.16.3.0/24 and 172.16.4.0/24 should prefer this direct link and should use any EBGP links only as backup. Traffic between the other addresses internal to AS 3 and AS 4 should use the EBGP links and should use the direct link only as a backup. Additionally, traffic from other autonomous systems can use the direct link as a backup route. If an EBGP link to AS 4 fails, for example, the neighboring AS can send traffic destined for AS 4 to AS 3, to be forwarded to AS 4 across the direct link.

8 AS 5 in Table 3-4 is a transit AS, and its IGP is IS-IS. The Level 2 area 47.0001 spans the entire AS. The internal networks are 192.168.9.0,192.168.10.0,192.168.11.0, and 192.168.12.0. Write IS-IS and BGP configurations for R9, RIO, and R11. Ensure that all external routes are known by the routers in the IS-IS domain and that all internal networks are advertised to all EBGP peers. Do not redistribute IS-IS routes into BGP

9 Modify the configurations written in Exercise 8 so that network 192.168.12.0 is known only by AS 4, and no other autonomous system.

10 Modify the configurations written in Exercise 9 so that AS 3 and AS 4 prefer the path through AS 1 to reach network 192.168.11.0.

11 The networks internal to AS 6 in Table 3-4 are 192.168.16.0, 192.168.17.0,

192.168.18.0, and 192.168.19.0. Write a BGP configuration for R12 that advertises these networks to the neighboring AS and that also advertises a summary route for the networks. The neighboring AS should advertise only the summary to other autonomous systems.

12 Modify the most recent configuration you wrote for R12's EBGP neighbor so that the neighbor does not accept prefixes that do not belong to the aggregate being advertised by R12, does not accept prefixes longer than 24 bits, and does not accept more than five prefixes.

13 Example 3-164 shows a BGP configuration for R7 in Table 3-4. The internal prefixes shown in Table 3-4 are advertised by OSPF.

example 3-164 BGP Configuration of Router R7

router bgp 3 redistribute ospf 1 neighbor NEIGHBORS peer-group neighbor NEIGHBORS ebgp-multihop 2 neighbor NEIGHBORS update-source LoopbackO neighbor NEIGHBORS route-map EX13 out neighbor 10.255.255.8 remote-as 4 neighbor 10.255.255.8 peer-group NEIGHBORS neighbor 10.255.255.9 remote-as 5 neighbor 10.255.255.9 peer-group NEIGHBORS neighbor 10.255.255.3 remote-as 1 neighbor 10.255.255.3 peer-group NEIGHBORS no auto-summary

ip classless ip as-path access-list 1 permit A1 2$ i access-list 1 permit 172.16.1.0 access-list 2 permit 172.16.3.0 i route-map EX13 permit 10 match ip address 1 set as-path prepend 2

i route-map EX13 permit 20 match ip address 2 set as-path prepend 1

i route-map EX13 permit 30 match as-path 1 set as-path prepend 4 5

i route-map EX13 deny 40

Explain the effects of route map EX13.

14 Router R1 in Figure 3-36 is a route reflector for routers R2, R3, and R4 and is connected to those neighbors via Frame Relay PVCs. Write a BGP configuration for R1 that provides full connectivity for the networks attached to the four routers. The cluster ID is 6500.

Figure 3-36 The Route Reflection Cluster for Configuration Exercise 14

Figure 3-36 The Route Reflection Cluster for Configuration Exercise 14

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