Wednesday 14 November 2012

Multicast: Configuring IGMP helper command:


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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