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Webcast-Catalyst9k
New Member

Multicast Null Flag !!

Hi every1, i was playing with PIM-SM, i am not going into the detail of my network but just showing you the output i want you guys to check.

R3#sh 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

(*, 225.5.5.5), 00:07:55/00:03:28, RP 10.1.4.4, flags: SJC

Incoming interface: Serial0/1, RPF nbr 12.0.0.1

Outgoing interface list:

Ethernet1/0, Forward/Sparse, 00:07:55/00:03:28

(20.0.0.1, 225.5.5.5), 00:00:20/00:02:39, flags:

Incoming interface: Serial0/0, RPF nbr 0.0.0.0

Outgoing interface list:

Ethernet1/0, Forward/Sparse, 00:00:20/00:03:28

(*, 224.0.1.40), 00:07:59/00:03:27, RP 10.1.4.4, flags: SJCL

Incoming interface: Serial0/1, RPF nbr 12.0.0.1

Outgoing interface list:

Ethernet1/0, Forward/Sparse, 00:07:53/00:03:27

Serial0/0, Forward/Sparse, 00:07:59/00:01:57

Kindly look for this statement

(20.0.0.1, 225.5.5.5), 00:00:20/00:02:39, flags:

Why there is no flag set ?? let me tell you that R3 is connected to a multicast client directly on its lan interface and when i tested my multicast network, client was able to get it successfully, but i am confused why no flag is set ?

am i missing something here ???

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Multicast Null Flag !!

Ovais,

You can use the mtrace command from the router connected to the receiver to find out to trace back to the source.

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
6 REPLIES
New Member

Re: Multicast Null Flag !!

Guys, its done, i was missing a config :-), but it was an interesting observation, no flag, no rpf neighbour but still multicast was successful :)

Re: Multicast Null Flag !!

What exactly was missing from the config? (So I can add it in my experience bank.)

Kevin Dorrell

Luxembourg

New Member

Re: Multicast Null Flag !!

Dear Kevin, actually on the SPT path, pim sparse wasnt enable, so thats why i was experiencing this issue, and 1 thing more, even after that i was seeing 2 flags against the same entry, "JT", can some 1 tell me how will you guys interpret this flag, T means that the router has switched over to SPT, whereas J means that its joining the SPT right ? how can they come both at the same time ?, i am really getting confused regarding the different flag combination, i referred to Beau famous book and no doubt its a great book but this area is really confusing me, does cisco gives any detail inside on what different combinations of flags mean ? ( any cisco doc ?? )

Kindly help me out in this.

Cisco Employee

Re: Multicast Null Flag !!

Ovais,

The mcast stream was simply forwarded down the shared tree as the source tree entry was imcomplete.

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Multicast Null Flag !!

Dear Hritter, can you tell me how to trace the multicast packet like we do for unicast packets ? i want to see that how it was going through the shared tree !

Thanks in advance and for clearing my confusion :)

Cisco Employee

Re: Multicast Null Flag !!

Ovais,

You can use the mtrace command from the router connected to the receiver to find out to trace back to the source.

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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