Answers to Chapter 6 Configuration Exercises

1 What global Cisco IOS Software command is required to enable IP multicast routing? Answer: ip multicast routing

2 Show the commands that enable PIM on an interface in dense mode sparse mode and sparse dense mode

Answer*

xp pim dense-mode lp pirn sparse-mode lp pim sparse-dense mode

3 Show the command to statically specify an^pP with an address of 172.18.20.4. Answer* lp pim rp-address 172.18.20.4

4 Write the configuration statements necessary to statically map groups 239.1.2.3 and 228.1.8.0 - 228.1.8.255 to RP 192.168.15.5, and group 239.6.7.8 to RP 192.168.20.10. Map all other groups to RP 192.168.25.1.

Answer*

ip pim rp-address 192.168.15.5 1 lp pim rp-address 192.168.20.10 2 ip pim rp-address 192.168.25.1

access-list 1 permit 239.1.2.3 0.0.0.0 access-list 1 permit 228.1.8.0 0.0.0.255 access-list 2 permit 239.6.7.8 0.0.0.0

5 All router interfaces shown m Figure 6-11 are running in sparse-dense mode. Show the relevant configurations m order for R1 to be the RP for only groups whose addresses begin with 226.13.0.0/24. R2 should only be the RP for groups whose addresses begin with 239.0.0.0/8. R3 is the mapping agent; ensure that the mapping agent will recognize only R1 and R2 as RPs, and only for the specified groups. All Auto-RP messages should have a TTL of 20.

Figure 6-11 The Topology for Configuration Exercises 5-8

Figure 6-11 The Topology for Configuration Exercises 5-8

Answer:

ip pim send rp announce LoopbackO scope 20 group list 1 !

access list 1 permit 226 13 0 0 0 0 0 255

ip pim send rp announce LoopbackO scope 20 group list 1 i access list 1 permit 239 0 0 0 0 255 255 255

ip pim rp announce filter rp list 10 group list 11 ip pim rp announce filter rp list 20 group list 21 ip pim send rp discovery LoopbackO scope 20

access list 10 permit 172 16 50 1

access list 11 permit 226 13 0 0 0 0 0 255

access list 20 permit 172 16 50 2

access list 21 permit 239 0 0 0 0 255 255 255

6 Given the configurations of Configuration Exercise 5 suppose a source originates traffic for group 228 23 14 135 and a member requests a join to that group What will happen?

Answer: Neither R1 nor R2 is configured to become the RP for that group Because all interfaces are running in sparse dense mode however, dense mode is invoked for the group and an SPT is built between the source and member.

7 Again referring to Figure 6 11 write the necessary configurations to enable the bootstrap protocol making R1 and R2 C RPs for the same group addresses described in Configuration Exercise 5 Make R3 the BSR and make R4 a backup BSR

Answer:

ip pim rp candidate LoopbackO group list 1 !

access list 1 permit 226 13 0 0 0 0 0 255

ip pim rp candidate LoopbackO group list 1 ยป

access list 1 permit 239 0 0 0 0 255 255 255

ip pim bsr candidate LoopbackO 50

ip pim bsr candidate LoopbackO 0

8 Write configurations for the topology in Figure 6 11 that allow multicast load balancing between source 172 16 1 75 and group member 172 16 2 100 Use unnumbered addressing on the tunnel interfaces referencing E0 and assume the IGP is advertising those addresses

Answer:

R6

interface TunnelO

ip unnumbered Ethernet0

ip pim sparse dense mode

tunnel source LoopbackO

tunnel destination 172 16 50

i

7

ip mroute 172 16 1 75 255 255

255 255 TunnelO

R7

interface TunnelO

ip unnumbered EthernetO

ip pim sparse dense mode

tunnel source LoopbackO

tunnel destination 172 16 50

6

9 Examine the configurations of Homburg and Porkpie shown in the case study

Multicast Load Sharing Each router is running OSPF in passive mode on the tunnel interfaces Why?

Answer: By putting the unicast protocol (in this case OSPF) into passive mode the protocol is aware of the interface addresses necessary for the multicast RPF function while at the same time preventing unicast traffic from using the tunnel

10 What is the purpose of the command ip pim spt threshold 100 group list 25?

Answer: When the arrival rate of packets for the group address or addresses specified in access list 25 exceeds 100 Kbps the PIM SM router switches from the shared tree to the shortest path tree

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