Configuring Multicast Routing and Forwarding 1105■ Specifying boundary interfaces, which form a closed multicast forwarding area,or■ Setting the minimum time to live (TTL) value required for a multicast packet tobe forwarded.You can configure a forwarding boundary specific to a particular multicast groupon all interfaces that support multicast forwarding. A multicast forwardingboundary sets the boundary condition for the multicast groups in the specifiedrange. If the destination address of a multicast packet matches the set boundarycondition, the packet will not be forwarded. Once a multicast boundary isconfigured on an interface, this interface can no longer forward multicast packets(including packets sent from the local device) or receive multicast packets.You can configure the minimum TTL required for a multicast packet to beforwarded on all interfaces that support multicast forwarding. Before beingforwarded from an interface, every multicast packet (including multicast packetfrom the local device) is subject to a TTL check:■ If the TTL value of the packet (already decremented by 1 on this router) is largerthan the minimum TTL value configured on the interface, the packet will beforwarded.■ If the TTL value of the packet is smaller than or equal to the minimum TTL valueconfigured on the interface, the packet will be discarded.Follow these steps to configure a multicast forwarding range:Configuring MulticastForwarding Table SizeToo many multicast routing entries can exhaust the router’s memory and thusresult in lower router performance. Therefore, the number of multicast routingentries should be limited. You can set a limit on the number of entries in themulticast routing table based on the actual networking situation and theperformance requirements. In any case, the number of route entries must notexceed the maximum number allowed by the system.If the configured maximum number of downstream nodes (namely, the maximumnumber of outgoing interfaces) for a routing entry in the multicast forwardingtable is smaller than the current number, the downstream nodes in excess of theconfigured limit will not be deleted immediately; instead they must be deleted bythe multicast routing protocol. In addition, newly added downstream nodescannot be installed to the routing entry in the forwarding table.To do... Use the command... RemarksEnter system view system-view -Enter interface view interface interface-typeinterface-number-Configure a multicastforwarding boundarymulticast boundarygroup-address { mask |mask-length }RequiredNo forwarding boundary bydefaultConfigure the minimumpacket TTL required for amulticast packet to beforwardedmulticast minimum-ttlttl-valueOptional1 by default
