Overlay as a link

Tony Tauber ttauber at 1-4-5.net
Wed Nov 19 17:42:54 UTC 2014

Hi Glen,

Perhaps I'm stating the obvious or something that's out of scope for what
you have in mind.

However, one property where they differ is that a physical link has a
physical capacity for carrying traffic (i.e., bandwidth).
A virtual interface inherits it's capacity from the physical link(s) that
underlie it.  Some may be locally attached but most will be indirect.

Hence it's not possible to know how near it is to its limits.

Again, maybe outside what you're thinking about, but you asked "what can
possibly be the difference".


On Wed, Nov 19, 2014 at 2:03 AM, Glen Kent <glen.kent at gmail.com> wrote:

> Hi,
> When youre doing overlay networking, i.e., you have tunnels from one
> virtual machine in a DC to another in another DC, then can i consider a
> tunnel between the two virtual machines as a "physical link" that exists in
> a regular network?
> I am wondering on what possibly can be the difference between a tunnel
> being considered as a link and a true physical link.
> I could run routing algorithms on both. The tunnel would only be considered
> as an interface. Or i could run BFD on both.
> Once difference that i can think of is that while you can send multiple
> frames together on a tunnel (for example if there are ECMP paths within the
> tunnel), you may not be able to send multiple frames at the same time on a
> physical link. Anything else?
> Glen

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