Multicast router passing traffic when OIL = NULL

Unanswered Question
Apr 11th, 2008

R4

/ \

R1 R3

| |

R2 R5

| |

--------- <----- Ethernet

|

R6

All interfaces have pim sparse-dense mode enabled.

All routers have R4 configured as static RP (4.4.4.4).

R6 has a igmp join-group 239.0.0.6 on its ethernet interface.

After R5 sends a ping to 239.0.0.6, R6 does reply.

However this is how the mroute tables look on R5 and R2:

R5#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

(*, 239.0.0.6), 00:35:13/stopped, RP 4.4.4.4, flags: SP

Incoming interface: Serial1/0, RPF nbr 172.12.35.3

Outgoing interface list: Null

(172.12.25.5, 239.0.0.6), 00:00:14/00:02:51, flags: PT

Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0

Outgoing interface list: Null

(*, 224.0.1.40), 00:49:30/00:02:16, RP 4.4.4.4, flags: SJPL

Incoming interface: Serial1/0, RPF nbr 172.12.35.3

Outgoing interface list: Null

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

(*, 239.0.0.6), 00:35:16/stopped, RP 4.4.4.4, flags: SP

Incoming interface: Serial1/0, RPF nbr 172.12.12.1

Outgoing interface list: Null

(172.12.25.5, 239.0.0.6), 00:00:17/00:02:44, flags: PT

Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0

Outgoing interface list: Null

(*, 224.0.1.40), 00:51:48/00:02:14, RP 4.4.4.4, flags: SJPCL

Incoming interface: Serial1/0, RPF nbr 172.12.12.1

Outgoing interface list: Null

How can R6 get the ping request when all the outgoing interface lists towards R6 are NULL?

Thanks,

-B

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Overall Rating: 4 (1 ratings)
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dodgerfan78 Fri, 04/11/2008 - 16:47

sorry for the bad drawing.

This is how it is

R4 - R1 - R2--|

R4 - R3 - R5--|-- R6

R6, R2 and R5 are on the same LAN

all other links are p2p.

R1 is also connected to R3.

R5 has to send the pim register up to R4, then R4 sends the traffic right back...

Harold Ritter Sat, 04/12/2008 - 05:25

Bryan,

This behavior is due to the fact that R5 receives the IGMP report message from R6 and therefore responds directly. Try issuing the ping from r3 instead and you should see a different behavior.

Regards,

dodgerfan78 Mon, 04/14/2008 - 16:08

Thanks. I do see different and interesting behavior. I am sure I will have many more questions :)

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