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[armd] Multicast in the data center [was Re: address resolution requirement from hosts to overlay edge nodes. Any opinion?]

Thomas Narten <narten@us.ibm.com> Wed, 15 February 2012 14:09 UTC

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To: Mike McBride <mmcbride7@gmail.com>
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Comments: In-reply-to Mike McBride <mmcbride7@gmail.com> message dated "Tue, 14 Feb 2012 13:16:28 -0800."
Date: Wed, 15 Feb 2012 09:07:38 -0500
From: Thomas Narten <narten@us.ibm.com>
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Subject: [armd] Multicast in the data center [was Re: address resolution requirement from hosts to overlay edge nodes. Any opinion?]
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Mike McBride <mmcbride7@gmail.com> writes:

> Large L2 overlay networks?  I don't know. Would be good to find out
> from the community about performance and scalability of multicast in
> the DC.

My impression is that many data centers do not enable IP multicast on
their routers. That means you can use link-local multicast (which
works fine within one IP subnet and doesn't really have scaling
issues). But if you want multicast that goes beyond one link (and IP
subnet), which is presumably necessary for an overlay like
VXLAN/NVGRE, that is where you have problems.

The question is not even whether L3 multicast scales. It's whether the
DC operater is willing to enable such multicast.

Thomas

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