196
C
HAPTER
15: M
ULTICAST
O
VERVIEW
RPF Check
The basis for an RPF check is a unicast route. A unicast routing table contains the
shortest path to each destination subnet. A multicast routing protocol does not
independently maintain any type of unicast route; instead, it relies on the existing
unicast routing information in creating multicast routing entries.
When performing an RPF check, a router searches its unicast routing table. The
specific process is as follows: The router automatically chooses an optimal unicast
route by searching its unicast routing table, 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
considers the path along which the packet from the RPF neighbor arrived on the
RPF interface to be the shortest path that leads back to the source.
Assume that unicast routes exist in the network, as shown in Figure 59. Multicast
packets travel along the SPT from the multicast source to the receivers.
Figure 61
RPF check process
■
A multicast packet from Source arrives to VLAN-interface 1 of Switch C, and
the corresponding forwarding entry does not exist in the multicast forwarding
table of Switch C. Switch C performs an RPF check, and finds in its unicast
routing table that the outgoing interface to 192.168.0.0/24 is VLAN-interface
2. This means that the interface on which the packet actually arrived is not the
RPF interface. The RPF check fails and the packet is discarded.
■
A multicast packet from Source arrives to VLAN-interface 2 of Switch C, and
the corresponding forwarding entry does not exist in the multicast forwarding
table of Switch C. The router performs an RPF check, and finds in its unicast
routing table that the outgoing interface to 192.168.0.0/24 is the interface on
which the packet actually arrived. The RPF check succeeds and the packet is
forwarded.
Source
192 .168 .0.1/24
Receiver
Receiver
Router A
Switch B
Switch C
Vlan -int2
Vlan -int1
Vlan -int1
Vlan -int2
Multicast packets
Destination/Mask
IP Routing Table on Switch C
192.168.0.0/24
Interface
Vlan -int2
Summary of Contents for Switch 4210 9-Port
Page 22: ...20 CHAPTER 1 CLI CONFIGURATION ...
Page 74: ...72 CHAPTER 3 CONFIGURATION FILE MANAGEMENT ...
Page 84: ...82 CHAPTER 5 VLAN CONFIGURATION ...
Page 96: ...94 CHAPTER 8 IP PERFORMANCE CONFIGURATION ...
Page 108: ...106 CHAPTER 9 PORT BASIC CONFIGURATION ...
Page 122: ...120 CHAPTER 11 PORT ISOLATION CONFIGURATION ...
Page 140: ...138 CHAPTER 13 MAC ADDRESS TABLE MANAGEMENT ...
Page 234: ...232 CHAPTER 17 802 1X CONFIGURATION ...
Page 246: ...244 CHAPTER 20 AAA OVERVIEW ...
Page 270: ...268 CHAPTER 21 AAA CONFIGURATION ...
Page 292: ...290 CHAPTER 26 DHCP BOOTP CLIENT CONFIGURATION ...
Page 318: ...316 CHAPTER 29 MIRRORING CONFIGURATION ...
Page 340: ...338 CHAPTER 30 CLUSTER ...
Page 362: ...360 CHAPTER 33 SNMP CONFIGURATION ...
Page 368: ...366 CHAPTER 34 RMON CONFIGURATION ...
Page 450: ...448 CHAPTER 39 TFTP CONFIGURATION ...
Page 451: ......
Page 452: ...450 CHAPTER 39 TFTP CONFIGURATION ...
Page 470: ...468 CHAPTER 40 INFORMATION CENTER ...
Page 496: ...494 CHAPTER 44 DEVICE MANAGEMENT ...