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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 17 Co nfiguring IGMP S noo ping and M VR
Configuring IG MP Snooping
Beginning i n privileged E X EC mo de , follow these s teps to g loba ll y ena ble IGM P snoo ping on the
switch:
To globa ll y dis able I GMP sno oping on al l V LAN in terfa ces, use th e no ip igmp snooping global
configurati on comm a nd.
Beginning in privileged EXEC mode, follo w these steps to enable IGMP snooping on a VLAN interface:
To disable IGMP snooping on a VLAN interface, use the no ip igmp snooping vlan vlan-id globa l
configurati on comm and for the specified VLAN numbe r.

Setting the Snooping Method

Multicast-capable router ports are added to the forwarding table for every Layer 2 multicast entry. The
switch learn s of such port s through one of these me thods:
•Snooping on IGMP queries, Protocol Independent Multicast (PIM) packets, and Distance Vector
Multicas t Routing Protocol (DVMRP) packets
•Listening t o Cisco Gro up Manageme nt Proto col (CGMP) packe ts from other routers
•Statically connecting to a multicast router port with the ip igmp snooping mrouter global
configurat ion c omm and
Yo u can configure the switch either to snoop on IGMP que ri es and PIM/ DVMRP packets or to listen to
CGMP se lf-joi n or p rox y-join pa ckets. By default , the swi tch snoops on PIM /DVMRP packets on all
VLANs. To lea rn o f mu ltica st r oute r po rts t hrough only CGMP pac k e ts, u se t he ip igmp snooping vlan
vlan-i d mr outer learn cgmp global configuration command. When this command is entered, the router
listens to only CG M P self-jo in and CGMP prox y-jo in pac kets and no other CG MP packe ts. To lear n of
multicast rout er po rt s th rou gh onl y PIM-DVMRP pac kets, use the ip igmp snooping vlan vlan-id
mrouter learn pim-dvmrp global co nfigurati on comm and.
Command Purpose
Step 1 configure terminal Enter globa l configurati on mode.
Step 2 ip igmp snooping Globally enable IGMP snooping in all existing VLAN interfaces.
Step 3 end Return to privileged EXEC mode.
Step 4 copy running-config startup-config (Optiona l) Save your entries in the co nfigurati on file.
Command Purpose
Step 1 configure terminal Enter globa l configurati on mode.
Step 2 ip igmp snooping vlan vlan-id Enabl e I GMP snoo ping on the VL AN int erface.
Step 3 end Return to privileged EXEC mode.
Step 4 copy running-config startup-config (Optiona l) Save your entries in the co nfigurati on file.