Cisco Catalyst 3550 Series, Software Configuration Manual, Page: 841 / 992

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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 34 Configuring IP Multicast Routing
Configuring Advanced DVMRP Interoperability Features
Rejecting a DVMRP Nonpruning Neighbor
By default, Cisco devices accept all DVMRP neighbors as peers, regardless of their DVMRP capability.
However, some non-Cisco devices run old versions of DVMRP that cannot prune, so they continuously
receive forwarded packets, wasting bandwidth.
Figure 34-13 shows this scenario.
Figure 34-13 Leaf Nonpruning DVMRP Neighbor
You can prevent the multilayer switch from peering (communicating) with a DVMRP neighbor if that
neighbor does not support DVMRP pruning or grafting. To do so, configure the multilayer switch (which
is a neighbor to the leaf, nonpruning DVMRP machine) with the ip dvmrp reject-non-pruners interface
configuration command on the interface connected to the nonpruning machine as shown in
Figure 34-14 .
In this case, when the multilayer switch receives DVMRP probe or report message without the
prune-capable flag set, the switch logs a syslog message and discards the message.
Si
Router A
Router B
Multilayer
switch
RP
Valid
multicast
traffic
Unnecessary
multicast
traffic
44970
Source router or RP
PIM dense mode
Leaf nonpruning
DVMRP device
Receiver
Stub LAN with no members