Use VLANs to limit Multicasting

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Hey guys,

I will try and make this make sense.  First of all if there is
another
group that this might be suited for please point me in the right
direction.


I have a situation where I have multiple IP cameras on L2 switches.
These switches are NOT IGMP capable.  The two backbone switches are
layer 3 and support multicasting just fine.  The manufacturer and the
customer want the cameras using multicasting.  Since the switches are
L2 without IGMP they will broadcast the multicast feed over all
interfaces.  These switches do support VLANS.  Could I create a VLAN
for every camera?  Will this work?

Re: Use VLANs to limit Multicasting
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It should work, but you need to keep in mind that if there is a device
that listens to traffic from both cameras, then it must be capable
of participating on multiple VLANs.  Also, typically (although it
doesn't have to be that way), a VLAN corresponds to an IP subnet,
so this might affect the way you assign addresses in the network.
Finally, if you do have a device listening to multiple cameras,
the port that goes to that device would most likely have to be
tagged.  Basically, what you want to do can be done, but there
are lots of gotchas you need to be aware of.

Anoop

Re: Use VLANs to limit Multicasting
anoop wrote:
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As multicast was mentioned I would presume the use of IP
multicast addresses.  Probably comp.protocols.tcp-ip would be
a better group for the IP specific part of the question.

-- glen


Re: Use VLANs to limit Multicasting

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Note that switches can be L2 and therefore not perform the proper IGMP
per se. But sometimes, they can do what's called "IGMP snooping." If
they do this, then they will not flood L2 multicast frames to all of
their ports. Only to those ports which are necessary to reach the IP
multicast end systems.

Creating VLANs for every camera might be possible, although that
depends on where the destinations are, whether they are likely to
move, etc. I'm not sure how this would be set up.

Bert

Re: Use VLANs to limit Multicasting
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yes. but the 1st Q is - do you care?

say your cameras are doing something fairly high quality - maybe 5 to 15
Mbps MPEG2?

with 10 cameras on a 100 Mbps LAN, then you have 50 Mbps of load (50%)

unless the cameras dont like the background traffic it is going to just
work.

These switches do support VLANS.  Could I create a VLAN
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you could, but that implies all your traffic flows go to the central
switches without any local flows - which might be a bit limiting if you have
users mixed in with the cameras.

and the 2nd Q - if you have all these cameras, lots of traffic, then why not
just replace the switches with something that does do IGMP snooping?

IGMP capable switches are not going to be expensive compared to good IP
cameras.....

--
Regards

stephen_hope@xyzworld.com - replace xyz with ntl



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