Chapter 7: Multicast Routing Configuration Guide7 - 2SSR User Reference Manual• Pruning, which is an operation DVMRP routers perform to exclude interfaces not inthe shortest path tree.DVMRP uses the Reverse Path Multicasting (RPM) algorithm to perform pruning.InRPM, a source network rather than a host is paired with a multicast group. RPM per-mits the SSR to maintain multiple multicast groups.On the SSR, DVMRP can be configured on a per-interface basis. An interface does nothave to run both DVMRP and IGMP. You can start and stop DVMRP independentlyfrom other routing protocols. IGMP starts and stops automatically with DVMRP.To support backward compatibility on DVMRP interfaces, you can configure the rout-er expire time and prune time on each SSR DVMRP interface. This lets it work witholder versions of DVMRP.You can use threshold values and scopes to control internetwork traffic on each DVM-RP interface. Threshold values determine whether traffic is either restricted or not re-stricted to a subnet, site, or region. Scopes define a set of multicast addresses of devicesto which the SSR can send DVMRP data. Scopes can include only addresses of deviceson a company's internal network and cannot include addresses that require the SSR tosend DVMRP data on the internet.You can also configure tunnels on SSR DVMRP interfaces. A tunnel is used to sendpackets between routers separated by gateways that do not support multicast routing.A tunnel acts as a virtual network between two routers running DVMRP. A tunnel doesnot run IGMP.Configure IGMPYou configure IGMP on the SSR by performing the following configuration tasks.• Creating IP interfaces.• Setting global parameters that will be used for all the interfaces on which DVMRPis enabled.• Configuring IGMP on individual interfaces. You do so by enabling and disablingIGMP on interfaces and then setting IGMP parameters on the interfaces on whichIGMP is enabled.Configuring IGMP on an IP InterfaceBy default IGMP is disabled on the SSR.
