Outside Multicast Server Example Inside Receiving Hosts

Tue, 15 Dec 2015 | SNPA

1. Host 10.0.0.11 sends an IGMP report:

Source 10.0.0.11 Destination 224.0.1.50 IGMP group 224.0.1.50

2. The security appliance accepts the packet, and IGMP places the inside interface on the output list for the group.

3. The security appliance forwards the IGMP packet to the multicast router:

Source 172.16.0.1 Destination 224.0.1.50 IGMP group 224.0.1.50

4. The router places the input interface on the output list for the group.

5. Packets from the multicast server arrive at the router, which forwards them to the necessary interfaces.

6. The security appliance accepts the packets and forwards them to the interfaces for the group.

172.16.0.1

Multicast Router

Multicast Server

IGMP Reports

Multicast Group 224.0.1.50

Multicast

Client 10.0.0.11

fw1(config)# access-list 120 permit udp any host 224.0.1.50

fw1(config)# interface ethernet2

fw1(config-if)# igmp access-group 120

fw1(config)# interface ethernet1

fw1(config-if)# igmp forward interface dmz

The figure shows the use of the interface command with corresponding igmp subcommands. Multicasting is permitted on the DMZ and inside interfaces. The igmp forward interface command enables the security appliance to forward IGMP reports from inside hosts to the multicast router on its DMZ interface.

In the example in the figure, host 10.0.0.11 joins multicast group 224.0.1.50. The security appliance enables host 10.0.0.11 to receive multicasts from the multicast server.

Configuring Other IGMP Options
1 ^^^^^^^^ c,iïuuuijiii 1
	firewall(config-if)#
	igmp version {1 \| 2}
	• Sets the version of IGMP to be used
	firewall(config-if)#
	igmp query-interval seconds
	• Configures the frequency at which IGMP query messages are sent by the interface
	firewall(config-if)#
	igmp query-max-response-time seconds
	• Sets the maximum query response time (for IGMP 2 only)
	fwl(config)# interface ethernetO fw1(config-if)# igmp version 2 fw1(config-if)# igmp query-interval 120 fw1(config-if)# igmp query-max-response-time 25
© 2005 Ci	sco Systems, Inc. All rights reserved. SNPA v4	1.0-8-25

There are some other IGMP options that can be set by an administrator. The administrator can choose an IGMP version and configure the IGMP timers with the igmp query-interval and igmp query-max-response-time commands. To specify the version of IGMP, use the igmp version command. This configures which version of IGMP is used on the subnet that is represented by the specified interface. The default is version 2.

IGMP v2 offers bandwidth-conserving features that are not available in version 1. The Leave Group message is one of these features. This message reduces the bandwidth waste between the time the last host in a subnet drops membership and the time the router times out for its queries and decides there are no more members present for that group.

For further information on the differences between IGMP v1 and IGMP v2, see RFC 2236.

Use the igmp query-interval command to configure the frequency at which IGMP query messages are sent by the interface. The default is 60 seconds. The permitted range of values is from 1 through 65535. Use the command no igmp query-interval to set the query interval back to the default.

The igmp query-max-response-time command specifies the maximum query response time and is available only with IGMP v2. The default is 10 seconds. The permitted range of values is from 1 to 25. Use the command no igmp query-max-response-time to set the query response time back to the default.

igmp query-interval seconds igmp query-max-response-time seconds igmp version {1 | 2}

igmp query-interval seconds igmp query-max-response-time seconds

query-interval	The query response time interval.
query-max-response-time	The maximum query response time interval.
seconds	The number of seconds to wait.

Protocol Independent Multicast Sparse Mode Overview

Multicast Server

Multic Clie

: Multicast Client

In Protocol Independent Multicast sparse mode (PIM SM), each data stream goes to a relatively small number of segments in the campus network. Instead of flooding the network to determine the status of multicast members, PIM SM defines a rendezvous point. The rendezvous point keeps track of multicast groups. When a user wants to send data, the user first sends to the rendezvous point. When a user wants to receive data, the user registers with the rendezvous point. After the data stream begins to flow from sender to rendezvous point to receiver, the routers in the path will optimize the path automatically to remove any unnecessary hops. PIM SM assumes that no hosts want the multicast traffic unless they specifically ask for it. Sparsemode protocols begin with an empty distribution tree and add branches only as the result of explicit requests to join the distribution.

PIM SM is optimized for environments in which there are many multipoint data streams. PIM SM is most useful when:

■ There are few receivers in a group

■ The type of traffic is intermittent

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