HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 69

{ The router automatically chooses an optimal MBGP route by searching its MBGP routing table, and using the IP address of the packet source as the destination address. The outgoing interface in the corresponding routing entry is the RPF interface and the next hop is the RPF neighbor. { The router automatically chooses an optimal static multicast route by searching its static multicast routing table, and using the IP address of the packet source as the destination address. The corresponding routing entry explicitly defines the RPF interface and the RPF neighbor. 2. The router selects one of these optimal routes as the RPF route. The selection process is as follows: { If configured to use the longest match principle, the router selects the longest match route from these optimal routes. If the three routes have the same mask, the router selects the route with the highest priority. If the three routes have the same priority, the router selects a route as the RPF route according to the sequence of static multicast route, MBGP route, and unicast route. { If not configured to use the longest match principle, the router selects the route with the highest priority. If the three routes have the same priority, the router selects a route as the RPF route according to the sequence of static multicast route, MBGP route, and unicast route. The "packet source" means different things in different situations: • For a packet traveling along the shortest path tree (SPT) from the multicast source to the receivers or the rendezvous point (RP), the packet source for RPF check is the multicast source. • For a packet traveling along the rendezvous point tree (RPT) from the RP to the receivers, or along the source-side RPT from the multicast source to the RP, the packet source for RPF check is the RP. • For a bootstrap message from the bootstrap router (BSR), the packet source for RPF check is the BSR. For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see "Configuring PIM." RPF check implementation in multicast Implementing an RPF check on each received multicast data packet would be a big burden to the router. The use of a multicast forwarding table is the solution to this issue. When creating a multicast routing entry and a multicast forwarding entry for a multicast packet, the router sets the RPF interface of the packet as the incoming interface of the (S, G) entry. After receiving an (S, G) multicast packet, the router first searches its multicast forwarding table: 1. If the corresponding (S, G) entry does not exist in the multicast forwarding table, the packet undergoes an RPF check. The router creates a multicast routing entry based on the relevant routing information and adds the entry into the multicast forwarding table, with the RPF interface as the incoming interface. { If the interface that received the packet is the RPF interface, the RPF check succeeds and the router forwards the packet to all the outgoing interfaces. { If the interface that received the packet is not the RPF interface, the RPF check fails and the router discards the packet. 2. If the corresponding (S, G) entry exists, and the interface that received the packet is the incoming interface, the router forwards the packet to all the outgoing interfaces. 3. If the corresponding (S, G) entry exists, but the interface that received the packet is not the incoming interface in the multicast forwarding table, the multicast packet undergoes an RPF check. { If the RPF interface is the incoming interface of the (S, G) entry, it indicates that the (S, G) entry is correct but the packet arrived from a wrong path. The packet will be discarded. { If the RPF interface is not the incoming interface, it indicates that the (S, G) entry has expired, and router replaces the incoming interface with the RPF interface. If the interface on which the 58