Multicast:
Configuring IGMP helper command:
·
When
there is a stub router and it cannot be configured to process multicast
messages, but still wants to receive multicast traffic, we can make use of IGMP
helper command.
·
Let
me take a topology of just 2 routers:
R1---—ser1/0-------------10.1.12.0--------ser1/0----R2
·
R1
is the stub router and doesn’t want to process multicast traffic
·
R2
is the server
·
Configuration
is very simple:
R1#show run int ser1/0
Building
configuration...
Current
configuration : 140 bytes
!
interface
Serial1/0
ip address 10.1.12.1 255.255.255.0
ip pim dense-mode
ip igmp helper-address 10.1.12.2
serial restart-delay 0
end
R1#show run
int loop0
Building
configuration...
Current
configuration : 115 bytes
!
interface
Loopback0
ip address 1.1.1.1 255.255.255.255
ip pim dense-mode
ip igmp join-group 227.27.27.27
end
R1#
R2#show run
int ser1/0
Building
configuration...
Current
configuration : 133 bytes
!
interface
Serial1/0
ip address 10.1.12.2 255.255.255.0
ip pim neighbor-filter 12
ip pim dense-mode
serial restart-delay 0
end
R2#show run
int loop0
Building
configuration...
Current
configuration : 82 bytes
!
interface
Loopback0
ip address 2.2.2.2 255.255.255.255
ip pim dense-mode
end
R2#
Observation:
·
IGMP
helper command is configure under R1’s Ser1/0
·
Since
R1 doesn’t want to process multicast messages, PIM neighbor-relationship is
blocked in R2’s Ser1/0 for R1’s ser1/0, 10.1.12.1
·
R1’s
loopback0 has configured as client to receive 227.27.27.27
·
Now,
I’m initiating ping form the server, R2’s loopback0
R2#ping
227.27.27.27 source 2.2.2.2
Type
escape sequence to abort.
Sending
1, 100-byte ICMP Echos to 227.27.27.27, timeout is 2 seconds:
Packet
sent with a source address of 2.2.2.2
Reply
to request 0 from 10.1.12.1, 84 ms
R2#
Observation:
·
Multicast
functionality is fine, R1 is receiving multicast traffic from R2.
·
Now,
let me see multicast routing tables:
R1#show ip
mroute
IP
Multicast Routing Table
Flags:
D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F
- Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP
created entry,
X - Proxy Join Timer Running, A -
Candidate for MSDP Advertisement,
U - URD, I - Received Source Specific
Host Report,
Z - Multicast Tunnel, z - MDT-data group
sender,
Y - Joined MDT-data group, y - Sending
to MDT-data group
Outgoing
interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD,
State/Mode
(*,
227.27.27.27), 00:11:33/stopped, RP 2.2.2.2, flags: SJCLF
Incoming interface: Serial1/0, RPF nbr
10.1.12.2
Outgoing interface list:
Loopback0, Forward/Dense, 00:09:31/00:00:00
(2.2.2.2,
227.27.27.27), 00:00:18/00:02:43, flags: LJTA
Incoming interface: Serial1/0, RPF nbr
10.1.12.2
Outgoing interface list:
Loopback0, Forward/Dense, 00:00:18/00:00:00
(*,
224.0.1.40), 10:53:50/00:02:54, RP 1.1.1.1, flags: SJCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial1/0, Forward/Dense, 00:15:51/00:00:00
Serial1/1, Forward/Sparse,
05:16:20/00:02:54
R1#
R2#show ip
mroute
IP
Multicast Routing Table
Flags:
D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F
- Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP
created entry,
X - Proxy Join Timer Running, A -
Candidate for MSDP Advertisement,
U - URD, I - Received Source Specific
Host Report,
Z - Multicast Tunnel, z - MDT-data group
sender,
Y - Joined MDT-data group, y - Sending
to MDT-data group
Outgoing
interface flags: H - Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD,
State/Mode
(*,
227.27.27.27), 00:00:36/stopped, RP 2.2.2.2, flags: SP
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list: Null
(2.2.2.2,
227.27.27.27), 00:00:36/00:02:23, flags: PTA
Incoming interface: Loopback0, RPF nbr
0.0.0.0
Outgoing interface list: Null
(*,
228.28.28.28), 08:42:46/00:02:41, RP 2.2.2.2, flags: S
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial1/1, Forward/Sparse, 08:42:46/00:02:41
(*,
224.0.1.40), 10:54:11/00:02:38, RP 2.2.2.2, flags: SJCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial1/1, Forward/Sparse,
05:14:42/00:02:38
R2#
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