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Prerequisites for IGMP Proxy
All devices on the IGMP UDL have the same subnet address. If all devices on the UDL cannot have the same subnet address, the upstream device must be configured with secondary addresses to match all of the subnets to which the downstream devices are attached.
IP multicast is enabled and the PIM interfaces are configured.
Use the following guidelines when configuring PIM interfaces for IGMP proxy:
Use PIM sparse mode (PIM-SM) when the interface is operating in a sparse-mode region and you are running static RP, bootstrap (BSR), or Auto-RP with the Auto-RP listener capability.
Use PIM sparse-dense mode when the interface is running in a sparse-dense mode region and you are running Auto-RP without the Auto-RP listener capability.
Use PIM dense mode (PIM-DM) when the interface is operating in dense mode and is, thus, participating in a dense-mode region.
Use PIM-DM with the proxy-register capability when the interface is receiving source traffic from a dense-mode region that needs to reach receivers that are in a sparse-mode region.
Information about IGMP Proxy
An IGMP proxy enables
hosts in a unidirectional link routing (UDLR) environment that are not directly
connected to a downstream router to join a multicast group sourced from an
The figure below
illustrates a sample topology that shows two UDLR scenarios:
routing scenario--A UDL device with directly connected receivers.
scenario--UDL device without directly connected receivers.
IGMP UDLs are
needed on the upstream and downstream devices.
following illustration and example uses routers in the configuration, any
device (router or switch) can be used.
Scenario 1--Traditional UDLR
Scenario (UDL Device with Directly Connected Receivers)
For scenario 1, no
IGMP proxy mechanism is needed. In this scenario, the following sequence of
User 2 sends an
IGMP membership report requesting interest in group G.
receives the IGMP membership report, adds a forwarding entry for group G on LAN
B, and proxies the IGMP report to Router A, which is the UDLR upstream device.
The IGMP report
is then proxied across the Internet link.
receives the IGMP proxy and maintains a forwarding entry on the unidirectional
Scenario 2--IGMP Proxy
Scenario (UDL Device without Directly Connected Receivers)
For scenario 2, the
IGMP proxy mechanism is needed to enable hosts that are not directly connected
to a downstream device to join a multicast group sourced from an upstream
network. In this scenario, the following sequence of events occurs:
User 1 sends an
IGMP membership report requesting interest in group G.
Router C sends
a PIM Join message hop-by-hop to the RP (Router B).
receives the PIM Join message and adds a forwarding entry for group G on LAN B.
periodically checks its mroute table and proxies the IGMP membership report to
its upstream UDL device across the Internet link.
creates and maintains a forwarding entry on the unidirectional link (UDL).
In an enterprise
network, it is desirable to be able to receive IP multicast traffic via
satellite and forward the traffic throughout the network. With unidirectional
link routing (UDLR) alone, scenario 2 would not be possible because receiving
hosts must be directly connected to the downstream device, Router B. The IGMP
proxy mechanism overcomes this limitation by creating an IGMP report for (*, G)
entries in the multicast forwarding table. To make this scenario functional,
therefore, you must enable IGMP report forwarding of proxied (*, G) multicast
static route (mroute) entries (using the
ipigmpmroute-proxy command) and enable the mroute proxy
service (using the
ipigmpproxy-service command) on interfaces leading to
PIM-enabled networks with potential members.
messages are not forwarded upstream, each downstream network and the upstream
network have a separate domain.
This step is performed to enable the forwarding of IGMP reports to a proxy service interface for all (*, G) forwarding entries in the multicast forwarding table.
In this example, theipigmpmroute-proxy command is configured on Gigabit Ethernet interface 1/0/0 to request that IGMP reports be sent to loopback interface 0 for all groups in the mroute table that are forwarded to Gigabit Ethernet interface 1/0/0.
Exits interface configuration mode and returns to global configuration mode.
Device(config)# interface loopback 0
Enters interface configuration mode for the specified interface.
In this example, loopback interface 0 is specified.
Device(config-if)# ip igmp helper-address udl gigabitethernet 0/0/0
Configures IGMP helpering for UDLR.
This step allows the downstream device to helper IGMP reports received from hosts to an upstream device connected to a UDL associated with the interface specified for the
In the example topology, IGMP helpering is configured over loopback interface 0 on the downstream device. Loopback interface 0, thus, is configured to helper IGMP reports from hosts to an upstream device connected to Gigabit Ethernet interface 0/0/0.
Device(config-if)# ip igmp proxy-service
Enables the mroute proxy service.
When the mroute proxy service is enabled, the device periodically checks the static mroute table for (*, G) forwarding entries that match interfaces configured with the
ipigmpmroute-proxy command (see Step 7) based on the IGMP query interval. Where there is a match, one IGMP report is created and received on this interface.
ipigmpproxy-service command is intended to be used with the
ipigmphelper-address (UDL) command.
In this example, the
ipigmpproxy-service command is configured on loopback interface 0 to enable the forwarding of IGMP reports out the interface for all groups on interfaces registered through the
ipigmpmroute-proxy command (see Step 7).
Ends the current configuration session and returns to privileged EXEC mode.
Device# show ip igmp interface
(Optional) Displays multicast-related information about an interface.
Device# show ip igmp udlr
(Optional) Displays UDLR information for directly connected multicast groups on interfaces that have a UDL helper address configured.
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