Ipv4 Multicast
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1IP
4 M
V
ULTICAST
packetlife.net
Layer 2 Addressing
Group Ranges
239.142.57.6
224.0.0.0/24
Local network control
11101111 10001110 00111001 00000110
224.0.1.0/24
Internetwork control
232.0.0.0/8
Source-specific
01-00-5E-0E-39-06
233.0.0.0/8
GLOP (RFC 3180)
00000001 00000000 01011110 00001110 00111001 00000110
239.0.0.0/8 Admin-scoped
Terminology
Common Groups
Reverse Path Forwarding (RPF)
Verifies that multicast traffic travels in the reverse direction of
224.0.0.1
All hosts
unicast traffic, away from the tree root
224.0.0.2
All routers
Cisco Group Management Protocol (CGMP)
224.0.1.39
Cisco RP Announce
A proprietary protocol used by switches to obtain multicast
membership information for end hosts (deprecated)
224.0.1.40
Cisco RP Discovery
Internet Group Management Protocol (IGMP)
Distribution Trees
Hosts send IGMP requests to local routers to join multicast groups
Shared
IGMP Configuration
A common set of links which carry all
multicast traffic; statically configured
IGMP Support
Router(config-if)# ip igmp [version <#>]
Source-Rooted
IGMP Snooping
Switch(config)# ip igmp snooping
Provides the shortest paths from the
source to receivers
Protocol Independent Multicast (PIM)
Dense Mode
IGMP
The initial tree encompasses all multicast routers; after a period of
IGMPv1
time, routers without IGMP members prune back branches
Original IGMP specification
Sparse Mode
IGMPv2
The tree is grown from a central rendezvous point out to the
Adds support for dynamic leave requests
multicast source and recipients
and querier election to original IGMP
Sparse-Dense Mode
IGMPv3
Allows a PIM-enabled interface to function in either sparse or dense
Adds multicast source filtering to v2
mode per group
IGMP Snooping
PIMv1
A switch passively inspects IGMP
Provides automatic RP discovery with Auto-RP (Cisco proprietary)
requests to determine which hosts
PIMv2
should receive multicast traffic
Automatic RP discovery is accomplished by the bootstrap router
(BSR) method (standard)
IGMP Troubleshooting
show ip igmp
PIM Configuration
show ip igmp group
ip multicast-routing
show ip igmp interface
!
interface FastEthernet0/0
show ip igmp snooping
ip pim {sparse-mode | dense-mode | sparse-dense-mode}
ip pim version {1 | 2}
ip igmp join-group
RP Configuration
PIM Troubleshooting
ip pim rp-address <IP>
Manual
show ip mroute
ip pim send-rp-discovery scope <TTL>
Auto-RP Mapping Agent
show ip pim interface
ip pim send-rp-announce <interface>
Auto-RP Candidate
show ip pim neighbor
BSR Candidate
ip pim bsr-candidate <interface>
show ip pim rp [mapping]
BSR RP Candidate ip pim rp-candidate <interface>
show ip rpf <IP>
by Jeremy Stretch
v2.0
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