3Com Router User Manual

							Configuring IGMP507
Configuring the Version 
Number of IGMP at the 
Router InterfaceIGMP Version 2 is able to configure query message timeout and the maximum 
query response time. All the systems in the same subnet must run the same IGMP 
version because the routers are not able to check the version number of IGMP 
currently running on the interface. 
Make the following configuration in the interface view.
Ta b l e 578   Configure the IGMP Version Number Run at Router Interface
By default, IGMP Version 2 is operates at the router interface.
If the host does not support IGMP Version 2, then the router must be configured 
to use IGMP Version 1. 
Configuring the Time 
Interval of IGMP Host 
Sending Query 
MessagesThe router periodically sends membership query messages to the network it 
connects to. The query interval timer sets the time interval. Subscribers can change 
the time interval of the IGMP host that sends query messages by configuring the 
query interval timer. 
Make the following configuration in the interface view. 
Ta b l e 579   Configure the Time Interval of IGMP Host Sending Query Messages
By default, the interval for sending query messages is 125 seconds. 
Configuring IGMP 
Maximum Query 
Response TimeAfter the host receives the query message periodically sent by the router, it starts 
delay timers for each of the multicast groups it joins. A random number between 
zero and the maximum response time will be adopted to serve as the initial value. 
The maximum response time is the query message assigned maximum response 
time (the maximum response time of IGMP Version 1 is fixed at 10 seconds). The 
host broadcasts the membership report to the router before the timer times out. If 
the router does not receive a membership report when the maximum query 
response time times out, it assumes that there is no local group member, and it 
does not send the received multicast message to the network it connects to. 
Make the following configuration in interface view.
Ta b l e 580   Configure IGMP Maximum Query Response Time
OperationCommand
Configure the version number of IGMP 
operating at router interface igmp version { 1 | 2 }
Restore the default value of the version 
number of IGMP operating at router 
interfaceundo igmp version
OperationCommand
Configure the time interval of IGMP host 
sending query messages igmp timer query seconds
Restore the default value of the time 
interval of IGMP host sending query 
messages undo igmp timer query 
OperationCommand
Configure IGMP maximum query response 
time igmp max-response-time seconds 
						

							508CHAPTER 34: CONFIGURING IGMP
The default maximum query response time is 10 seconds but ranges from 1 to 25 
seconds.
This configuration can only be carried out if the current router interface is 
operating IGMP Version 2. 
Configuring Subnet 
Querier Survival TimeWhen there are several routers operating IGMP in a subnet, one router is chosen 
to serve as a querier to take charge of sending query messages to other routers in 
the network segment. In the network initialization, all the routers in the network 
segment act as querier by default, and send general query messages to all the 
multicast hosts in the subnet the routers connect to. Meanwhile, they compare 
the receiving IP address of the query message interface with the sending IP address 
of the query message interface. The router with the minimum IP address in the 
subnet will be chosen as querier, and the other routers become non-queriers. 
All the non-queriers start the other querier present interval timer. Before the timer 
times out, if the query message from the querier is received, the timer resets. If the 
timer times out, all the routers reset as querier. The querier selection process 
restarts. 
Make the following configuration in the interface view.
Ta b l e 581   Configure Subnet Querier Survival Time
By default, subnet querier timeout is 250 seconds. 
This configuration can only be carried out if the current router interface is 
operating IGMP Version 2.
Displaying and 
Debugging IGMPTa b l e 582   Display and Debug IGMP
After the previous configuration, execute the display command in all views to 
display IGMP configuration, and to verify the effect of the configuration. Execute 
the debugging command in system view to debug IGMP.
IGMP Configuration 
ExampleRouter A, Router B and a PC connect to one another through a Hub, and their 
interfaces are all fast Ethernet (FE).
Restore the default value of IGMP 
maximum query response time undo igmp max-response-time
OperationCommand
Configure subnet Querier survival timeigmp timer querier-present seconds
Restore the default value of the subnet 
Querier survival time undo igmp timer querier-present
OperationCommand
Display the group membership status in 
the direct connecting subnetdisplay igmp group [ group-address | 
interface type number ]
Display IGMP interface configuration 
informationdisplay igmp interface [ type number 
]
Turn on the switch of IGMP debugging 
informationdebugging igmp { all | event | host | 
packet | timer } 
						

							IGMP Configuration Example509
Figure 162   IGMP network diagram
1Configure the IP addresses of the interfaces of Router A, Router B and the PC.
[RouterA]interface e0
[RouterA-Ethernet0]ip address 10.16.1.3 24
[RouterB]interface e0
[RouterB-Ethernet0]ip address 10.16.1.2 24
2Execute the multicast routing-enable command on 3Com A and 3Com B to 
enable multicast routing.
[RouterA] multicast routing-enable
[RouterB] multicast routing-enable
Quidway A
PCQuidway B
HUB 10.16.1.3
10.16.1.2
10.16.1.0/24
10.16.1.1Router ARouter B 
						

							510CHAPTER 34: CONFIGURING IGMP 
						

							35
CONFIGURING PIM-DM
This chapter covers the following topics:
■PIM-DM Overview
■PIM-DM Configuration
■Displaying and Debugging PIM-DM
■PIM-DM Configuration Example
PIM-DM OverviewProtocol Independent Multicast--Dense Mode (PIM-DM) is applicable to the 
following conditions: 
■The transmitter and the receiver are close to each other, and there are a large 
number of multicast group receiving members in the network.
■Multicast packet traffic is large. 
■Multicast packet traffic is continuous.
PIM-DM constructs a multicast distribution tree from the source PIM router to all 
the other nodes employing unicast routing table. When sending a multicast 
packet, PIM-DM assumes that all the hosts in the network are ready for receiving 
the multicast packet. The multicast source begins distributing multicast packets to 
the downstream nodes of the network. The nodes without multicast group 
members will send prune message to the upstream router and inform it that there 
is no need for it to distribute data to the downstream nodes any more. When new 
members appear in the prune area, PIM-DM sends graft message to enable the 
pruned path to restore to distribution status. This mechanism is called 
broadcast-prune process. 
The PIM-DM broadcast-prune mechanism continues periodically. PIM-DM adopts 
reverse path forwarding (RPF) technology in the broadcast-prune process. When a 
multicast packet arrives, the router first judges the correctness of the arriving path. 
If the arriving port is the one directed to the multicast source according to the 
unicast routing instruction, the multicast packet is considered to be from the 
correct path. Otherwise, the multicast packet will be considered a redundant 
packet and will be discarded.
PIM-DM includes the following kinds of messages: 
■PIM Hello Message: PIM hello message is periodically sent neighbor interface in 
the same network segment to establish a relationship with the PIM-DM 
neighbors by the router interface operating the PIM-DM protocol. In addition, a 
designed router (DR) is required, in the IGMPv1, to send a host-query message. 
Meanwhile, the hello message takes charge of choosing a DR for the router  
						

							512CHAPTER 35: CONFIGURING PIM-DM
operating IGMPv1 (each PIM router periodically broadcasts a hello message, 
and the router with higher IP address is chosen to be the DR).
■Graft Message: The host informs the router which multicast groups it wants to 
join by a IGMP membership report message. At this time, the port sends a graft 
message to the upstream router. After the upstream router receives a graft 
message, it adds this port to the forwarding list of the multicast group. 
■Graft ACK Message: After the upstream router receives the graft message, it 
needs to send graft acknowledgement (ACK) message to the downstream 
router sending the graft message. 
■Prune Message: If the router interface forwarding list is empty, or the interface 
forwarding list becomes empty, the prune message will be sent to the 
upstream router to inform it to delete the downstream router from its interface 
neighbor list. 
■Assert Message: A shared network segment can have two upstream routers 
simultaneously. If both of them forward multicast packets to it, the 
downstream routers of this network segment will probably receive two same 
multicast packets. In order to avoid this condition, PIM-DM adopts the assert 
message mechanism. If a router receives multicast packets at the forwarding 
port of a shared LAN, it requires all the routers operating PIM-DM (group 
address is 224.0.0.13) to send an assert message. The downstream routers 
determine the winner by comparing the specific domains of the assert message 
according to the relevant series of rules. The router with little message 
preference wins. If the preference is the same, the router with the smaller 
message metric value wins. If the message metric value is the same, the router 
with the bigger IP address wins. The winner serves as the transmitter of the 
network segment, while the loser sends an output interface prune message. 
PIM-DM itself does not have a routing discovery mechanism, so it has to depend 
on a specific unicast routing protocol. Thus the protocol implementation is quite 
simple.
PIM-DM ConfigurationPIM-DM configuration includes tasks that are described in the following sections: 
■Enabling Multicast Routing
■Starting the PIM-DM Protocol
■Configuring the Time Interval for Hello Messages  
Enabling Multicast 
RoutingOnly after the multicast routing is enabled, can routers receive multicast packets. 
Make the following configuration in the system view.
Ta b l e 583   Enable Multicast Routing
By default, the system disables the multicast routing. 
OperationCommand
Enable multicast routingmulticast routing-enable
Disable multicast routingundo multicast routing-enable 
						

							Displaying and Debugging PIM-DM513
Starting the PIM-DM 
ProtocolYou must start the PIM-DM protocol at each interface. By default, the system 
disables the PIM-DM protocol.
Make the following configuration in the interface view. 
Ta b l e 584   Start/Disable PIM-DM Protocol
Configuring the Time 
Interval for Hello 
Messages After the interface starts PIM-DM protocol, it will periodically send to all the PIM 
routers (group address is 224.0.0.13) hello messages to find neighbors. PIM 
query-interval timer determines the time interval. If the interface receives the hello 
message, it means that there are adjacent PIM routers for this interface, and this 
interface adds the neighbor to its interface neighbor list. If the interface does not 
receive any hello message from the neighbors in the interface neighbor list within 
a specific period, it is assumed that the neighbor has left the multicast network. 
The time interval of sending hello message can be configured according to the 
bandwidth and the type of the network to which the interface connects. 
Make the following configuration in the interface view.
Ta b l e 585   Configure the Time Interval of Interface Sending Hello Messages
By default, the time interval of interface sending hello messages is 30 seconds. 
Displaying and 
Debugging PIM-DMTa b l e 586   Display and Debug PIM-DM
OperationCommand
Start PIM-DM protocolpim dm
Disable PIM-DM protocolundo pim dm
OperationCommand
Set the time interval of interface sending 
hello messages pim timer hello seconds
Restore the default value of the time 
interval of interface sending hello 
messagesundo pim timer hello
OperationCommand
Display multicast forwarding list 
informationdisplay multicast forwarding-table [ 
group-address | source-address ]
Display multicast core routing tabledisplay multicast routing-table [ 
group-address | source-address ]
Display IP multicast forwarding table 
informationdisplay multicast forwarding-table
Display PIM protocol interface informationdisplay pim interface [ type number ]
Display PIM protocol multicast routing 
table informationdisplay pim routing-table [ *g [ 
group-address ] | **rp [ rp-address ] 
| { group-address | source-address } 
]
Display PIM adjacent routers informationdisplay pim neighbor [ interface type 
number ]
Turn on the switch of multicast 
forwarding table debugging information debugging multicast forwarding
Turn on the switch of PIM general 
debugging informationdebugging pim common { all | event | 
packet | timer } 
						

							514CHAPTER 35: CONFIGURING PIM-DM
After making the previous configuration, execute the display command in all 
views to display the running of the PIM-DM configuration, and to verify the effect 
of the configuration. Execute the 
debugging command in system view to debug 
PIM-DM.
PIM-DM Configuration 
ExampleIn this example, the multicast source server is the multicast source, while RECEIVER 
1 and RECEIVER 2 are the two receivers of this multicast group. 
Figure 163   PIM-DM configuration and networking
1Enable multicast routing protocol
[Router] multicast routing-enable
2Enable PIM-DM protocol
[Router] interface Ethernet 0
[Router-Ethernet0] pim dm
[Router-Ethernet0] interface serial 0
[Router-Serial0] pim dm
[Router-Serial0] interface serial 1
[Router-Serial1] pim dm
Turn on the switch of PIM-DM debugging 
informationdebugging pim dm { alert | all | mrt 
| timer | warning | { recv | send } { 
all | assert | graft | graft-ack | 
join | prune } }
RouterR outer
Router
Multic as t
source
RECEIVER 1
RECEIVER 2 
						

							36
CONFIGURING PIM-SM
This chapter covers the following topics:
■PIM-SM Overview
■PIM-SM Configuration
■Displaying and Debugging PIM-SM
■PIM-SM Configuration Example
■Troubleshooting PIM-SM
PIM-SM OverviewProtocol Independent Multicast--Sparse Mode (PIM-SM) is used in the following 
conditions: 
■The distribution of the group members is relatively separate and the range is 
comparatively wide.
■The network bandwidth resource is limited. 
PIM-SM is independent of any specific unicast routing protocol. PIM -SM is called 
protocol independent because it can use the route information entered by any 
routing protocol, such as unicast protocols like OSPF, RIP, or multicasting protocols 
like DVRMP in the multicasting routing information base (RIB). It supposes that all 
the routers will not send multicast packets to the multicast group unless there is an 
explicit transmission request. PIM-SM informs all the PIM-SM routers of multicast 
information by configuring a rendezvous point (RP) and a bootstrap router (BSR). 
And it reduces data messages and controls the network bandwidth occupied by 
the messages occupy by allowing routers to explicitly join and leave multicast 
groups. PIM-SM constructs an RP path tree (RPT) with the RP its root so as to make 
the multicast packets transmitted along with the RPT. 
When a host joins a multicast group, the directly connected router sends a joining 
message to the RP PIM. The first hop router of the transmitter registers the 
transmitter at RP. The receivers DR adds the receiver to the RPT. Using the RPT 
with the RP its root not only reduces the protocol state that routers need 
maintenance, which improves the scalability of the protocol and reduces the 
routers processing cost, but also supports a large number of simultaneous 
multicast groups. When the data traffic flow reaches a certain degree, the data 
will switch from the RPT to the shortest path tree based on source so as to reduce 
the network delay. 
PIM-SM mainly includes the following kinds of messages: 
■PIM Hello Message: A PIM hello message is periodically sent to the other 
neighbor interface by a router interface that operates PIM-DM protocol in the 
same network segment. It establishes neighborship with the PIM-DM  
						

							516CHAPTER 36: CONFIGURING PIM-SM
neighbors. The hello message also takes charge of choosing a DR for the router 
operating IGMPv1.
■Register Message: When the DR receives the multicast message sent by the 
host in the local network, it encapsulates it in the register message and unicasts 
it to the RP to distribute the message along the RP tree. The source address in 
the IP header of the register message is DR address, and the destination 
address is RP address. 
■Register-Stop Message: It is unicast to the transmitter of the register message 
by RP to inform the transmitter to stop sending register messages. 
■Join/Prune Message: This message is sent in the direction of the source or RP. 
The join message establishes the RPT or SPT. When the receiver leaves the 
group, the prune message is used to prune the RPT or SPT. The join message 
and the prune message are placed in one message, but either of such two 
kinds of messages can be empty.
■Bootstrap Message: The router sends this message from all the interfaces 
except on that interface receiving this kind of message. This kind of message is 
generated in BSR, and is forwarded by all the routers. It is used to inform all the 
routers of the RP-Set information collected by BSR. 
■Assert Message: When there are multiple routers in the multiple access 
network, and the output interface for the routing item of a router receives 
multicast message, this kind of message is used to specify the transmitter. 
■Candidate-RP-Advertisement Message: This message is unicast to BSR by the 
candidate RP to report the service group address set of this candidate RP. 
PIM-SM ConfigurationPIM-SM configuration includes tasks that are discribed in the following sections: 
■Enabling Multicast Routing
■Starting the PIM-SM Protocol
■Configuring the Candidate BSR
■Configuring the Candidate RP
■Configuring the PIM-SM Domain Boundary 
■Configuring the Time Interval for Sending a Hello Message 
■Configuring the Threshold of the Shortest Path 
Enabling Multicast 
RoutingMake the following configuration in the system view.
Ta b l e 587   Enable/Disable Multicast Routing
By default, the system disables multicast routing.
Starting the PIM-SM 
ProtocolThe PIM-SM protocol is configured at each interface in turn. In normal conditions, 
the PIM-SM protocol should be started at all interfaces. 
Make the following configuration in the interface view.
OperationCommand
Enable multicast routingmulticast routing-enable
Disable multicast routingundo multicast routing-enable