Understanding Dvmrp - Cisco 3750G - Catalyst Integrated Wireless LAN Controller Configuration Manual

Chapter 40 Configuring IP Multicast Routing
Figure 40-2
source 151.10.3.21
is forwarded.
Table 40-1
Network
151.10.0.0/16
198.14.32.0/32
204.1.16.0/24
PIM uses both source trees and RP-rooted shared trees to forward datagrams (described in the
DM" section on page 40-4
differently for each:
•
•
Sparse-mode PIM uses the RPF lookup function to decide where it needs to send joins and prunes:
•
•
DVMRP and dense-mode PIM use only source trees and use RPF as previously described.

Understanding DVMRP

DVMRP is implemented in the equipment of many vendors and is based on the public-domain mrouted
program. This protocol has been deployed in the MBONE and in other intradomain multicast networks.
Cisco routers and multilayer switches run PIM and can forward multicast packets to and receive from a
DVMRP neighbor. It is also possible to propagate DVMRP routes into and through a PIM cloud. The
software propagates DVMRP routes and builds a separate database for these routes on each router and
multilayer switch, but PIM uses this routing information to make the packet-forwarding decision. The
software does not implement the complete DVMRP. However, it supports dynamic discovery of DVMRP
routers and can interoperate with them over traditional media (such as Ethernet and FDDI) or over
DVMRP-specific tunnels.
OL-8550-02
RPF Check
Multicast
packet from
Gigabit Ethernet 0/1
Layer 3 switch
Gigabit Ethernet 0/3
Routing Table Example for an RPF Check
Port
Gigabit Ethernet 1/0/1
Gigabit Ethernet 1/0/3
Gigabit Ethernet 1/0/4
and the
If a PIM router or multilayer switch has a source-tree state (that is, an (S,G) entry is present in the
multicast routing table), it performs the RPF check against the IP address of the source of the
multicast packet.
If a PIM router or multilayer switch has a shared-tree state (and no explicit source-tree state), it
performs the RPF check on the RP address (which is known when members join the group).
(S,G) joins (which are source-tree states) are sent toward the source.
(*,G) joins (which are shared-tree states) are sent toward the RP.
Understanding Cisco's Implementation of IP Multicast Routing
Multicast
packet from
source 151.10.3.21
packet is discarded.
Gigabit Ethernet 0/2
Gigabit Ethernet 0/4
"PIM SM" section on page
Catalyst 3750 Switch Software Configuration Guide
40-5). The RPF check is performed
"PIM
40-7