All things related to multicast

["Wallace, Steven S" <>]

It's my understanding that all IGMP snooping Ethernet switches will not
forward Host Reports to any segment other than to the querier.  This is to
insure all members are forced to send host reports, so that the switch can
identify all segment that contain members.  I'm not sure if our HP switches
send all host reports to the querier or just a period one.

Steven 

> -----Original Message-----
> From: Gordon Rogier 
> [mailto:]
> Sent: Wednesday, July 12, 2000 7:13 PM
> To: 
> 
> Subject: 3Com 3300 switch and IGMP Multicast Learning
> 
> 
> I am having a little problem with the 3Com SuperStack II 3000 ethernet
> switch and IGMP Multicast Learning.  I am interested to see 
> if anyone else
> has experience and/or reported this issue to 3Com.
> 
> This issue was identified up to and including the latest SSII 
> 3000 code
> available of v2.43.
> 
> When in IGMP Multicast Learning mode, it appears to me that 
> the 3Com 3000
> does not forward the IGMPv2 Membership Report (8bit 'type' 
> field of 0x16)
> to which is sent to the 224.0.0.2 group in response to an IGMP Group
> Specific Query (it does not send it anywhere, esp. back towards the
> querier router). Because this membership report does not get 
> back to the
> querier and in the case that this is _not _ the only receiver on the
> segment, the mcast router prunes down the group until a General Query
> rolls around.  This effectively can cut off the mcast traffic
> inappropriately and cause mcast traffic 'ghosting' type 
> problems for most
> applications.  Effectively bad systemic jitter at best.
> 
> Turning off IGMP Multicast Learning clearly does "flood" all 
> mcast traffic
> as expected.
> 
> It basically looks like the 3Com 3300 actually "eats" all 
> IGMP packets and
> makes specific forwarding decisions for IGMP packets.
> 
> Has anyone else seen this problem???
> 
> I am quite concerned about this.  It is quite debatable to me if this
> feature should be turned on or off.  If high bandwidth 
> applications are
> present, it almost has to be on for reasonable traffic 
> control..... but,
> it you need to support lower bandwidth applications like SLP services,
> then this could cause some noticable ghosting issues... and 
> for video type
> services where side by side receivers are 'channel-surfing' 
> they can very
> easily cause noticable IGMP induced "jitter" in the traffic 
> stream on the
> local segment.
> 
> If I can figure out a valid support email address for 3Com I 
> will forward
> this them also. 
> 
> --*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*--
> Gordon Rogier                        
> 
>   
>           
> Network Engineer                     785-864-0381wk 785-550-4468 cell
> Great Plains Network                 785-864-9330 FAX
>