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When a multicast-capable internetwork is between two subnets with broadcast-only-capable hosts, you can convert broadcast traffic to IP multicast traffic at the first hop router and convert it back to broadcast traffic at the last hop router to deliver the packets to the broadcast clients. You can thus take advantage of the multicast capability of an intermediate IP multicast helper. Configuring an intermediate IP multicast helper allows the transport of broadcast packets across an IP multicast-enabled network, thereby preventing unnecessary replication at the intermediate routers.
For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks" section.
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•Prerequisites for Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks
•Information About Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks
•How to Configure an Intermediate IP Multicast Helper Between Broadcast-Only Networks
•Configuration Examples for an Intermediate IP Multicast Helper Between Broadcast-Only Networks
•You understand the concepts documented in the "IP Multicast Technology Overview" module.
•You have IP multicast configured in your network environment and your IP multicast network is between broadcast-only networks. See the "Configuring Basic IP Multicast" module for more information about configuring IP multicast.
To configure an intermediate IP multicast helper between broadcast-only networks, you should be familiar with the following concept:
•Intermediate IP Multicast Helper Capability
An intermediate IP multicast helper allows the transport of broadcast packets across an IP multicast-enabled network, thereby preventing unnecessary replication at the intermediate routers.
When configuring an intermediate IP multicast helper between broadcast-only networks, you must configure the first hop router to convert broadcast traffic to IP multicast traffic and the last hop router to convert IP multicast traffic back to broadcast traffic.
This section contains the following procedures:
•Configuring the First Hop Router to Convert Broadcast Traffic to IP Multicast Traffic (required)
•Configuring the Last Hop Router to Convert the IP Multicast Traffic Back to Broadcast Traffic (required)
Perform this task to convert broadcast traffic to IP multicast traffic on the first hop router. The first hop router is on the border between the broadcast-only network and IP multicast network.
•This task assumes that you have an IP multicast network configured between two broadcast-only networks. For more information about configuring IP multicast, see the "Configuring Basic IP Multicast" module.
1. enable
2. configure terminal
3. access-list access-list-number {deny | permit} udp {any | [host] source-address source-wildcard} [operator [port]] {any | [host] destination-address destination-wildcard} [operator [port]]
4. interface type number
5. ip multicast helper-map broadcast group-address access-list
6. exit
7. ip forward-protocol udp [port]
8. end
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Step 1 |
enable Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
configure terminal Router# configure terminal |
Enters global configuration mode. |
Step 3 |
access-list access-list-number {deny | permit} udp {any | [host] source-address source-wildcard} [operator [port]] {any | [host] destination-address destination-wildcard} [operator [port]] Router# access-list 105 permit udp host 126.1.22.199 host 126.1.22.255 eq 4000 |
Creates an extended IP access list to control which UDP broadcast packets are translated. Note For more information about creating IP access lists, see the "Creating an IP Access List and Applying It to an Interface" module in the Cisco IOS XE Security Configuration Guide: Securing the Data Plane, Release 2. |
Step 4 |
interface type number Router(config)# interface gigabitethernet 0/0/0 |
Enters interface configuration mode. •For the type and number arguments, select an incoming interface on the first hop router that is receiving broadcast-only traffic |
Step 5 |
ip multicast helper-map broadcast group-address access-list Router(config-if)# ip multicast helper-map broadcast 239.254.2.5 105 |
Allows IP multicast routing in a multicast-capable internetwork between two broadcast-only internetworks. •In the configuration on the first hop router, the ip multicast helper-map command is used with the broadcast keyword and group-address argument to specify the traffic to be converted from broadcast to multicast. The multicast group address specified for the group-address argument is the address to which the converted traffic will be directed. •For the access-list argument, specify the name or number of the access list created in Step 3 of this task. Note The form of the ip multicast helper-map command used in the configuration of the first hop router is different from the form of the command used in the configuration of the last hop router. See the "Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks: Example"section for an example of this task. |
Step 6 |
exit Router(config-if)# exit |
Exits interface configuration mode and returns to global configuration mode. |
Step 7 |
ip forward-protocol udp [port] Router(config)# ip forward-protocol udp 4000 |
Configures the forwarding of UDP broadcast messages destined for the specified port. |
Step 8 |
end Router(config)# end |
Exits global configuration mode and enters privileged EXEC mode. |
Perform this task to convert the IP multicast traffic back to broadcast traffic on the last hop router. The last hop router is on the border between the intermediate IP multicast network and broadcast-only network.
•This task assumes that you have an IP multicast network configured between two broadcast-only networks. For more information about configuring IP multicast, see the "Configuring Basic IP Multicast" module in the Cisco IOS IP XE Multicast Configuration Guide, Release 2.
1. enable
2. configure terminal
3. access-list access-list-number {deny | permit} udp {any | [host] source-address source-wildcard} [operator [port]] {any | [host] destination-address destination-wildcard} [operator [port]]
4. interface type number
5. ip multicast helper-map group-address broadcast-address access-list
6. exit
7. interface type number
8. ip directed-broadcast
9. exit
10. ip forward-protocol udp [port]
11. end
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Step 1 |
enable Router> enable |
Enables privileged EXEC mode. •Enter your password if prompted. |
Step 2 |
configure terminal Router# configure terminal |
Enters global configuration mode. |
Step 3 |
access-list access-list-number {deny | permit} udp {any | [host] source-address source-wildcard} [operator [port]] {any | [host] destination-address destination-wildcard} [operator [port]] Router# access-list 105 permit udp host 126.1.22.199 host 126.1.22.255 eq 4000 |
Creates an extended IP access list to control which UDP broadcast packets are translated. Note For more information about creating IP access lists, see the "Creating an IP Access List and Applying It to an Interface" module in the Cisco IOS XE Security Configuration Guide: Securing the Data Plane, Release 2. |
Step 4 |
interface type number Router(config)# interface gigabitethernet 1/0/0 |
Enters interface configuration mode. •For the type and number arguments, select an incoming interface on the last hop router that is receiving IP multicast traffic. |
Step 5 |
ip multicast helper-map group-address broadcast-address access-list Router(config-if)# ip multicast helper-map 239.254.2.5 126.1.28.255 105 |
Allows IP multicast routing in a multicast-capable internetwork between two broadcast-only internetworks. •In the configuration on the last hop router, the ip multicast helper-map command is used with the group-address and broadcast-address arguments to specify the traffic to be converted from IP multicast to broadcast. The multicast group address specified for the group-address argument is the address of the traffic to be converted from IP multicast to broadcast. The broadcast address specified for the broadcast-address argument is the address to which the broadcast traffic will be sent. •For the access-list argument, specify the name or number of the access list created in Step 3 of this task. Note The form of the ip multicast helper-map command used in the configuration of the first hop router is different from the form of the command used in the configuration of the last hop router. See the "Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks: Example"section for an example of this task. |
Step 6 |
exit Router(config-if)# exit |
Exits interface configuration and returns to global configuration mode. |
Step 7 |
interface type number Router(config)# interface gigabitethernet 2/0/0 |
Enters interface configuration mode. •For the type and number arguments, select an outgoing interface on the last hop router that is facing the destination broadcast-only subnet. |
Step 8 |
ip directed-broadcast Router(config-if)# ip directed-broadcast |
Enables the translation of a directed broadcast to physical broadcasts. |
Step 9 |
exit Router(config-if)# exit |
Exits interface configuration and returns to global configuration mode. |
Step 10 |
ip forward-protocol udp [port] Router(config)# ip forward-protocol udp 4000 |
Configures the forwarding of UDP broadcast messages destined for the specified port. |
Step 11 |
end Router(config)# end |
Exits global configuration mode and enters privileged EXEC mode. |
This section provides the following configuration example:
•"Configuring an Intermediate IP Multicast Helper Between Broadcast-Only Networks: Example" section
This example shows how to configure an intermediate IP multicast helper between broadcast-only networks. The topology used for this example is illustrated in Figure 1.
Figure 1 IP Multicast Helper Example Topology
In this example, a server on the LAN connected to Gigabit Ethernet interface 0/0/0 of Router A is sending a UDP broadcast traffic with a source address of 126.1.22.199 and a destination address of 126.1.22.255:4000. The configuration on the first hop router converts the broadcast traffic arriving at incoming Gigabit Ethernet interface 0/0/0 destined for UDP port 4000 to IP multicast traffic. The access list permits traffic being sent from the server at 126.1.22.199 being sent to 126.1.22.255:4000. The traffic is sent to group address 239.254.2.5. The ip forward-protocol command specifies the forwarding of broadcast messages destined for UDP port 4000.
Note This example primarily displays the configuration related to configuring an intermediate IP multicast helper. Protocol Independent Multicast-Sparse Mode (PIM-SM) is the multicast protocol used in this example. PIM-SM requires the use of a rendezvous point (RP). For more information about configuring RPs, see the Configuring Basic IP Multicast module in the Cisco IOS XE IP Multicast Configuration Guide.
The configuration on the last hop router converts the IP multicast traffic at incoming Gigabit Ethernet interface 1/0/0 back to broadcast at outgoing Gigabit Ethernet interface 2/0/0. Again, not all multicast traffic emerging from the multicast network should be converted from multicast to broadcast, only the traffic destined for 126.1.22.255:4000.
The configurations for Router A and Router C are as follows:
Router A—First Hop Router Configuration
interface gigabitethernet 0/0/0
ip address 126.1.22.1 255.255.255.0
ip pim sparse-mode
ip multicast helper-map broadcast 239.254.2.5 105
access-list 105 permit udp host 126.1.22.199 host 126.1.22.255 eq 4000
ip forward-protocol udp 4000
Router C—Last Hop Router Configuration
interface gigabitethernet 1/0/0
ip address 126.1.26.1 255.255.255.0
ip pim sparse-mode
ip multicast helper-map 239.254.2.5 126.1.28.255 105
!
interface gigabitethernet 2/0/0
ip address 126.1.28.1 255.255.255.0
ip directed-broadcast
access-list 105 permit udp host 126.1.22.199 any eq 4000
ip forward-protocol udp 4000
The following sections provide references related to configuring an intermediate IP multicast helper between broadcast-only networks.
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Basic IP multicast concepts, configuration tasks, and examples |
"Configuring Basic IP Multicast" module |
Overview of the IP multicast technology area |
"IP Multicast TechnologyOverview" module |
IP multicast commands: complete command syntax, command mode, command history, command defaults, usage guidelines, and examples |
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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None |
To locate and download MIBs for selected platforms, Cisco IOS XE releases, and feature sets, use Cisco MIB Locator found at the following URL: |
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No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
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Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.