Configuring Unidirectional Link Routing
UDLR Tunnel Configuration Task List
IPC-508
Cisco IOS IP Configuration Guide
In the scenario in Figure 82, the following sequence of events occurs:
1. User 1 joins multicast group G.
2. Router C sends a Protocol Independent Multicast (PIM) join message hop-by-hop to the rendezvous
point (Router B).
3. Router B receives the PIM join message and adds a forwarding entry for group G on LAN B.
4. Router B periodically checks its mroute table, and forwards an IGMP report for each multicast group
in which it is the reporter.
5. Router A creates and maintains a forwarding entry on the UDL.
In an enterprise network, for example, it is desirable to be able to receive IP multicast traffic via satellite
and forward the traffic throughout the network. With IGMP UDLR alone, this scenario is not possible
because receiving hosts must be directly connected to the downstream router. IGMP Proxy overcomes
this limitation by creating an IGMP report for (*, G) entries in the multicast forwarding table. To make
this scenario functional, you must configure PIM sparse mode (PIM-SM) in the network, make the UDL
downstream router the rendezvous point (RP) for a select set of addresses, and configure mroute proxy
on interfaces leading to PIM-enabled networks with potential members. When the UDL downstream
router has a (*, G) forwarding entry for an mroute proxy interface, an IGMP report for the group is
created and sent to a loopback interface (IGMP Proxy interface). The loopback interface then uses the
same mechanism as IGMP UDLR to forward reports upstream.
Note Because PIM messages are not forwarded upstream, each downstream network and the upstream
network has a separate domain.
UDLR Tunnel Configuration Task List
To configure a UDLR tunnel, perform the required tasks described in the following section:
•Configuring UDLR Tunnel (Required)

Prerequisite

Before configuring UDLR tunnel, ensure that all routers on the UDL have the same subnet address. If
all routers on the UDL cannot have the same subnet address, the upstream router must be configured with
secondary addresses to match all the subnets that the downstream routers are attached to.

Configuring UDLR Tunnel

When configuring a UDLR tunnel, you must configure both the upstream and downstream routers to
meet the following conditions:
•You need not assign an IP address to the tunnel (you need not use the ip address or ip unnumbered
interface configuration commands).
•You must configure the tunnel endpoint addresses.
•The tunnel mode defaults to GRE.