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Multicasting with an SGE2010P


Hi,

I have just purchased a SGE2010p switch. I am hoping to multicast with windows deployment services WDS
and also hoping someone might be able to give a basic explanation (configuration would be brilliant!) on the process.

On the switch webpage, we ticked the box for IGMP snooping. WDS configured with multicasting and that part of
it works. Getting transfer rates of 16,000KBps (according to WDS console). Would have thought gigabyte should be
better than that, but still better than the 250KBps without IGMP snooping.

The problem is that all traffic is still being sent to all other ports on the switch. There is only the switch
and no routers involved. Some documents indicate IGMP querier is required, but there seems no option for that that
I can find. I believe we later enabled autolearn (but not certain - dont have access to the switch at the moment)
and then WDS broke <again>.

So I am hoping someone can please educate me!

What needs to be done to prevent the switch from forwarding data to all ports
Is AutoLearn the same as an IGMP querier?
What is bridge multicast forwarding? Sounds like passing multicasts across routers?.
Do we need to create a multicast group on the switch? I would think no, that WDS does all that.
Does this switch support MLD snooping?

Any help appreciated
thank you!
2 REPLIES
Cisco Employee

Re: Multicasting with an SGE2010P

In addition to enabling IGMP snooping did you define a Multicast Group also?  If not this may likely be the cause of all ports receiving the multicast traffic.  Page 247 of the Admin Guide addresses setting this up as well as the IGMP snooping.  Another resource for Partners with these types of design related questions is the Partner Design Support (PDS).  They provide support for all Cisco Small Business & Small Business Pro categories of products.

Regards,

Glenn

New Member

Re: Multicasting with an SGE2010P

That's not going to work; manually defining groups means static multicasting (ie not dynamic nor scalable). That sort of defeats the purpose of IGMP snooping.

The problem is Microsoft's default multicast range is incompatible with IGMP and switches.

When a multicast layer 3 address is mapped to layer 2 (for the switch multicast layer 2 address), only the last 23 bits of the IPv4 address come across. The other bits are lost as we need specify the ethernet OUID owned by iana.  (01-00-5e).

So the default range by microsoft 239.0.0.1-239.0.0.255 maps out at the ethernet layer:  01-00-5e-00-00-01 to 01-00-5e-00-00-ff
The problem is, the 224.x.x.x mulicast control messages also map out like that, e.g. 224.0.0.1 maps to 01-00-5e-00-00-01.

So 224.0.0.1 and 239.0.0.1 map to the same ethernet (layer 2) mac address. Therefore the switch has no alternative but to broadcast as 224.0.0.1 = all nodes.
So try changing the default WDS address to something that wont get confused by the switch, e.g. 239.67.54.3 to 239.67.54.255.

Have tested this in a lab only but should fix the problem.

bye

Oh, bridge multicast forwarding is for when the traffic needs to be forwarded (ie to another switch or router). Filtering is only to be touched to block all multicast traffic - perhaps for permanent groups that need to be manually configured. You dont need to touch that.

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