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CGMP switch got flooded when 6509 got "%MCAST-6-DELGDA:Deleting a GDA"

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Jun 12th, 2002
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We have a c6509 as central switch with some IGMP snooping switches and CGMP switches. The problem is that every time when c6509 pop up a console message of "%MCAST-6-DELGDA:Deleting a GDA 01-00-5e-02-11-0b in vlan 1", all ports in those CGMP switch got flooded with multicast packet for a while until the c6509 show a message of received an IGMP report. From the MRTG graph, it shows a lot of traffic coming from sc0, too. However, there is no problem with those IGMP-snooping switches.


My configuration on c6509 (router part) is:

!

ip multicast-routing

!

!

!

interface Vlan1

ip pim sparse-mode

ip cgmp

!


My CGMP switch config is:

!

#cgmp

set cgmp enable

!


Is there any mistakes that I have done ?

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milan.kulik Thu, 06/13/2002 - 00:00
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Are you really routing multicasts from one VLAN to other in your network?

If you use pim just for "translation" IGMP to CGMP in one VLAN (that's what I do), simly remove ip multicast-routing from your router config.


HTH,

Milan

yeunggordon Thu, 06/13/2002 - 17:52
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We have tried it but the result of the removal of "ip multicast-routing" will stop the IGMP query action and therefore stop the IGMP to CGMP translation.


From: http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/switch_r/xrdscmd2.htm#1029668


The command description of "ip multicast-routing" is :

When IP multicast routing is disabled, the Cisco IOS software does not forward any multicast packets.


So, the "ip multicast-routing" command is must for IGMP to be run properly.


Also, is it normal as shown below that 15/1 is joining all multicast groups ?


> (enable) show multicast group

VLAN Dest MAC/Route Des [CoS] Destination Ports or VCs / [Protocol Type]

---- ------------------ ----- -------------------------------------------

1 01-00-5e-00-01-01 3/10,15/1

1 01-00-5e-00-01-16 2/8,3/13,15/1

1 01-00-5e-00-01-18 3/10,3/15,15/1

1 01-00-5e-00-01-28 15/1

1 01-00-5e-00-01-3c 4/29,15/1

1 01-00-5e-02-11-0b 15/1

1 01-00-5e-02-11-0c 3/10,15/1

1 01-00-5e-02-7f-fe 3/13,15/1

1 01-00-5e-02-7f-ff 3/13,15/1

1 01-00-5e-07-07-00 3/13,15/1

1 01-00-5e-7f-ff-fa 3/14,4/29,15/1


I found that even there is no one join a group, say, 01-00-5e-02-11-0b,

the 15/1 still join the group. I believe that it's cause of the DELGDA message per 300 seconds and cause multicast flooding to all ports in CGMP switch but we still don't know how to prevent 15/1 from joining all the groups !!!


2002 Jun 14 09:38:23 HKT +08:00 %MCAST-6-DELGDA:Deleting a GDA 01-00-5e-02-11-0b in vlan 1

2002 Jun 14 09:43:23 HKT +08:00 %MCAST-6-DELGDA:Deleting a GDA 01-00-5e-02-11-0b in vlan 1


Please help !!! Thanks


Best regards,

Gordon



milan.kulik Thu, 06/13/2002 - 22:20
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Gordon,

you are not correct, the removal of "ip multicast-routing" will not stop the IGMP to CGMP translation. It will only stop multicast forwarding from one VLAN to others. See

http://www.cisco.com/warp/public/473/38.html')">http://www.cisco.com/warp/public/473/38.html for more info.

Regarding port 15/1: This behaviour is typical for trunks. If 15/1 is not a trunk I would span this port to a protocol analyzer and see is the connected device is really sending IGMP join packets.


Another question: Is 01-00-5e-02-11-0b the only multicast group causing your trouble or are there several of them?

Regards,

Milan

yeunggordon Sat, 06/15/2002 - 20:13
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From my observation, if there are no one joining any multicast group, the

"show multicast group" command will show all groups that are subscribed

by interface 15/1. I observe that for those groups that are "ONLY" subscribed by 15/1 (e.g. no one subscribed the group), the DELGDA message will show up once every 300sec. During that instant, all CGMP switch will be flooded with the multicast packets until the 6509 received any IGMP report. The worst case is... if there are no one sending any IGMP report, all the CGMP switch port will get flooded forever ....

milan.kulik Sun, 06/16/2002 - 23:35
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It seems like default CAM aging time (300 sec) to me. Are you sure that your CGMP work fine on your switches? I would connect an IGMP device to an CGMP switch and observe if the switch detects the port belonging to the multicast group correctly....


Regards,

Milan


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