How to avoid flooding with broadcaste/multicaste frame

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Jan 20th, 2009
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How to avoid flooding with broadcaste/multicaste frame


Scenario: I would to distribute ghost image from a server in server vlan A to another end devices in same vlan B but in different Cisco switch. Do I have to be aware flooding issue in my network and in the case how can I avoid? Tanks in advance.


sfanayei

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Giuseppe Larosa Tue, 01/20/2009 - 01:16
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Hello Shanryar,


as explained in this recent thread


http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=LAN%2C%20Switching%20and%20Routing&topicID=.ee71a04&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cc2cd67


you need to enable :

ip multicast routing

+

ip pim sparse-dense mode

on L3 SVI interfaces Vlan A and Vlan B (or router subinterfaces)


on L2 only switches you need to enable ip igmp snooping


verify with

sh ip igmp snooping


if it is enabled on L2 switches


Hope to help

Giuseppe


sfanayei Tue, 01/20/2009 - 04:29
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Hi Giuseppe

Many tanks for your fast reply. Can you tell too that how I can to monitore the process?


I appreciat!


sfanayei


Giuseppe Larosa Tue, 01/20/2009 - 04:42
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Hello Shanryar,


on the router L3 switch use


sh ip igmp groups


look at the time the group is joined



sh ip mroute multicast-group-address


check that the oilist contains Vlan A and/or Vlan B



on the L2 switch

check if IGMP is enabled with:


sh ip igmp snooping



you can see the multicast addresses in


sh mac-address-table int type x/y


there is a second section after unicast MAC addresses


Hope to help

Giuseppe


mariov652 Tue, 01/20/2009 - 04:52
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Hi,


Giuseppe helped me out earlier with that post he recommended, so I'll give him a break and try to answer your question.


You should be able to check that IGMP snooping is active on the switch by typing "sh ip igmp snooping"


This gives you the IGMP snooping global settings as well as individual settings per vlan.


An easy way to check if broadcasts are only forwarded to the ports you want is to use a network sniffer (such as wireshark) on 2 or more systems in the same VLAN.


Start by monitoring both systems without the multicast requestor application running.


Then, on one system, start the application (and hence the multicast requests) - You should see multicast broadcasts only to that system and not the other.



I hope that helps.

sfanayei Tue, 01/20/2009 - 05:09
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Hi,

Tanks a lot. I will test it like you said.


sfanayei

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