91-414 Data Communications II
LAB5 IP MULTICAST
Sources: Mastering Networks, Liebeherr & Zarki
Kurose & Ross
Resources: man pages msend, mreceive
IETF IGMP RFC
Save data needed in directory /labdata. Save files to floppy.
Send answers to numbered questions via email.
Ethereal data traces should be submitted in printed or printable form.
Note: On the PCs, eth0 is the port below and eth1 is the port above.
PC
PC1
PC2
PC3
PC4
Eth0
10.0.1.11/24
10.0.1.21/24
10.0.1.31/24
10.0.1.41/24
Eth1
10.0.2.12/24
10.0.2.22/24
10.0.2.32/24
10.0.2.42/24
Cisco Router Ethernet0
Ethernet1
Router1
10.0.1.1/24 10.0.2.1/24
Multicast on a single segment
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Reboot the PCs.
Connect eth0 interfaces of the four PCs to the same hub.
Make sure the eth1 interface on each of the four PCs is disabled
Verify that the PCs are connected to the console ports of routers. PC1 should be
connected to Router1 and so on. Verify that you can connect to the routers using
the Kermit command.
Use ping to verify that all interfaces are correctly configured.
On each PC, add a route to address 224.0.0.0/8 for eth0:
o route add –net 224.0.0.0/8 dev eth0.
Start ethereal to capture traffic on eth0 of PC1.
Start a multicast sender on PC1:
o msend –I eth0 –g 224.1.2.3 –p 4444 –text “PC1”
Observe the traffic with ethereal:
1. What are the MAC address and destination IP address of the transmitted packets?
2. What is the transport protocol used?
3. Which IGMP messages do you observe? How many IGMP packets do you
observe?
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91-414 Data Communications II
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Start a multicast receiver on PC2 and PC3
o mreceive –g 224.1.2.3 –p 4444
4. What, if any, extra packets do PC2 and PC3 generate?
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Start a new multicast sender on PC4
o msend –g 224.1.2.3 –p 4444 –text “PC4”
5. How do the receivers handle the transmissions from multiple senders?
6. There is no IP multicast support for TCP. What are the implications? Speculate
why there is no multicast version for TCP.
7. What is the impact of adding and deleting multicast senders and receivers to a
multicast group.
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Stop everything.
Enable IGMP at a router
Set up Router1 so that it used IGMP. For now, don’t enable multicast packet forwarding
since there is only one IP network segment, but set up for pim dense mode as the
multicast routing protocol.
Router> enable
Router(config)# ip routing
Password: <enable secret>
Router# configure terminal
Router(config)# no ip routing
Router(config)# ip routing
Router(config)# no ip multicast-routing
Router(config-if)# interface Ethernet0
Router(config-if)# no shutdown
Router(config-if)# ip pim dense-mode
Router(config-if)# end
The following IOS commands may be useful:
ip mroute
- displays the multicast routing table for all groups
clear ip mroute *
- deletes all multicast routing table entries
show ip igmp groups - displays multicast groups with members
IGMP Packets
 Start ethereal on PC4. Observe the IGMP packets that are exchanged between
hosts and the router.
 Start multiple senders and/or receivers on the PCs. Start each in a separate
window.
On PC1:
msend –g 224.1.1.1 –p 1111 –t 8 –text “PC1”
msend –g 224.2.2.2 –p 2222 –t 8 –text “PC1”
mreceive –g 224.3.3.3 –p 3333
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91-414 Data Communications II
On PC2:
msend –g 224.3.3.3 –p 3333 –t 8 –text “PC2”
msend –g 224.1.1.1 –p 1111 –t 8 –text “PC2”
On PC3:
msend –g 224.2.2.2 –p 2222 –t 8 –text “PC3”
msend –g 224.3.3.3 –p 2222 –t 8 –text “PC3”
On PC4:
mreceive –g 224.1.1.1 –p 1111
mreceive –g 224.2.2.2 –p 2222
mreceive –g 224.3.3.3 –p 3333
8. Which types of IGMP message do you see?
9. What are their TTL values:
10. What is the destination IP address of IGMP Leave messages?
On PC4, ping a mcast group (ping –c 5 224.0.0.1)
224.0.0.1 is a special mcast group that all IP interfaces that are IP mcast enabled are
joined to.
11. How many hosts responded?
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Stop everything
Multicast on multiple segments
This part involves how IP multicast works on a network with multiple IP neworks.
Here, two segments are connected by a multicast enabled router. For each segment,
the router keeps track of which hosts have joined a multicast group.
Ethernet0
10.0.1.1/24
Router1
Ethernet1
10.0.2.1/24
Hub2
Hub1
Eth0
10.0.1.11/24
24
PC1
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Eth0
10.0.1.21/24
24
PC2
Eth1
10.0.2.32/24
24
PC3
PC4
Eth1
10.0.2.42/24
24
Set up the network as above using instructions from previous labs. Note that
PC3 and PC4 are connected to the hub via Eth1.
For each PC, add a default route for Router1. For PC1 and PC2, a default
route is set to 10.0.1.1. For PC3 and PC4, a default route is set to 10.0.2.1.
On each PC add a second route for 224.0.0.0/8.
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91-414 Data Communications II
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o On PC1 and PC2: route add –net 224.0.0.0/8 dev eth0
o On PC3 and PC4: route add –net 224.0.0.0/8 dev eth1
Disable the unused interfaces on each PC.
Use the ping command to verify that all interfaces are correctly configure.
Set up Router1 so that if runs IGMP on both interfaces but IP multicast
forwarding remains disabled on the router. Refer to instructions above.
Start an ethereal session on PC1 that captures data on eth0 and a session on
PC3 that captures data on eth1.
Use the same commands above to start multicast senders and receivers as
were used above.
12. At the router, show the igmp groups and include the output in the lab report.
 Stop everything.
Enable multicast forwarding
 Make sure PIM-DM is enabled on both router interfaces.
 Enable IP multicast forwarding on Router 1 (Router(config) ip multicastrouting).
 Start an ethereal capture of IGMP as before.
 Start msends and mreceives as before.
13. What are the destination IP addresses of IGMP queries from the multicast router?
14. What is the destination IP address of an IGMP report?
15. Is a report generated for every host for each group it joins?
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