Hi Everyone,
Im playing around with multicast and found an interesting issue where I
have the following setup:
r6 -- r1 --- r9 --- r5
I'm running pim sparse mode on all interfaces and ospf for unicast
connectivity.
I have R6 setup as the RP with a static command on R6, R1 and R5 'ip pim
rp-address 215.0.0.6'.
R9 has *no* RP configuration.
I join a group on R6s loopback and ping from R5. The ping is successful.
This is confusing to me as the way I understand PIM, R5 would send a group
'Register' to the RP via R9. R9 would receive this but having no knowledge
of the RP, would simply drop the packet and respond back with a Register
Stop.
However, somehow the group register is making its way to the RP, SPT is
built and pings flow.
How/why is R9 forwarding the PIM register message if it does not know where
the RP is?
Thanks
James
PIM Debugs below show the tree being built.
r5
----
R5(config)#do ping 232.8.8.8
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 232.8.8.8, timeout is 2 seconds:
*Mar 1 01:20:28.727: PIM(0): Check RP 215.0.0.6 into the (*, 232.8.8.8)
entry
*Mar 1 01:20:28.727: PIM(0): Send v2 Register to 215.0.0.6 for 215.0.0.5,
group 232.8.8.8
*Mar 1 01:20:28.727: IP(0): s=215.0.0.5 (Loopback0) d=232.8.8.8 id=187,
ttl=254, prot=1, len=100(100), mroute olist null
*Mar 1 01:20:28.751: PIM(0): Received v2 Join/Prune on FastEthernet0/1.59
from 215.5.9.9, to us
*Mar 1 01:20:28.751: PIM(0): Join-list: (215.0.0.5/32, 232.8.8.8), S-bit
set
*Mar 1 01:20:28.755: PIM(0): Add FastEthernet0/1.59/215.5.9.9 to
(215.0.0.5, 232.8.8.8), Forward state, by PIM SG Join.
R5(config)#do un all
All possible debugging has been turned off
R5(config)#do ping 232.8.8.8
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 232.8.8.8, timeout is 2 seconds:
Reply to request 0 from 215.1.6.6, 28 ms
R5(config)#
r9
---
R9(config-subif)#
*Mar 1 01:20:26.907: PIM(0): Received v2 Join/Prune on FastEthernet0/1.19
from 215.1.9.1, to us
*Mar 1 01:20:26.907: PIM(0): Join-list: (215.0.0.5/32, 232.8.8.8), S-bit
set
*Mar 1 01:20:26.907: PIM(0): Add FastEthernet0/1.19/215.1.9.1 to
(215.0.0.5, 232.8.8.8), Forward state, by PIM SG Join
*Mar 1 01:20:26.907: PIM(0): Insert (215.0.0.5,232.8.8.8) join in nbr
215.5.9.5's queue
*Mar 1 01:20:26.907: PIM(0): Building Join/Prune packet for nbr 215.5.9.5
*Mar 1 01:20:26.907: PIM(0): Adding v2 (215.0.0.5/32, 232.8.8.8), S-bit
Join
*Mar 1 01:20:26.907: PIM(0): Send v2 join/prune to 215.5.9.5
(FastEthernet0/1.59)
R9(config-subif)#
R9(config-subif)#do sh ip mroute
(*, 232.8.8.8), 00:01:40/stopped, RP 0.0.0.0, flags: SP
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list: Null
(215.0.0.5, 232.8.8.8), 00:01:40/00:02:33, flags: T
Incoming interface: FastEthernet0/1.59, RPF nbr 215.5.9.5
Outgoing interface list:
FastEthernet0/1.19, Forward/Sparse, 00:01:40/00:02:48
R9(config-subif)#
r1
---
R1(config)#
*Mar 1 01:20:27.907: PIM(0): Received v2 Join/Prune on FastEthernet0/0.16
from 215.1.6.6, to us
*Mar 1 01:20:27.907: PIM(0): Join-list: (215.0.0.5/32, 232.8.8.8), S-bit
set
*Mar 1 01:20:27.907: PIM(0): Check RP 215.0.0.6 into the (*, 232.8.8.8)
entry
*Mar 1 01:20:27.907: PIM(0): Add FastEthernet0/0.16/215.1.6.6 to
(215.0.0.5, 232.8.8.8), Forward state, by PIM SG Join
*Mar 1 01:20:27.907: PIM(0): Insert (215.0.0.5,232.8.8.8) join in nbr
215.1.9.9's queue
*Mar 1 01:20:27.907: PIM(0): Building Join/Prune packet for nbr 215.1.9.9
*Mar 1 01:20:27.907: PIM(0): Adding v2 (215.0.0.5/32, 232.8.8.8), S-bit
Join
R1(config)#
*Mar 1 01:20:27.907: PIM(0): Send v2 join/prune to 215.1.9.9
(FastEthernet0/0.19)
R1(config)#
r6
---
R6(config)#
*Mar 1 01:20:28.439: PIM(0): Received v2 Register on FastEthernet0/0.16
from 215.5.9.5
*Mar 1 01:20:28.439: for 215.0.0.5, group 232.8.8.8
*Mar 1 01:20:28.447: PIM(0): Insert (215.0.0.5,232.8.8.8) join in nbr
215.1.6.1's queue
*Mar 1 01:20:28.447: PIM(0): Forward decapsulated data packet for
232.8.8.8 on Loopback0
*Mar 1 01:20:28.447: PIM(0): Building Join/Prune packet for nbr 215.1.6.1
*Mar 1 01:20:28.447: PIM(0): Adding v2 (215.0.0.5/32, 232.8.8.8), S-bit
Join
*Mar 1 01:20:28.447: PIM(0): Send v2 join/prune to 215.1.6.1
(FastEthernet0/0.16)
R6(config)#do un all
All possible debugging has been turned off
R6(config)#
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