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[mininet-discuss] Significance of DPID

Rushit Parekh rparekh081052 at gmail.com
Tue Apr 22 13:46:35 PDT 2014


dpid=datapath index
controller manages datapath indexes


On Tue, Apr 22, 2014 at 11:20 AM, Murphy McCauley <murphy.mccauley at gmail.com
> wrote:

> This is really an OpenFlow question, and it's answered in the OpenFlow
> spec.  Sort of.
>
> The short of it is that it's a unique identifier for a switch so that
> someone/something (e.g., an OpenFlow controller) can uniquely identify the
> switch.  It's 64 bits, so it's not an ethernet address, though the spec
> claims the lower 48 bits are *intended* to be the switch's ethernet
> address.  In my opinion, this statement has always been a bit confusing --
> traditionally, a switch isn't an endpoint, so what addresses does a switch
> even really have?  The only answer that makes sense to me is that it's the
> ethernet address associated with the IP address used for the OpenFlow
> control channel.  But in implementations, this is not always the case
> because the OpenFlow control channel often may originate from one of
> several interfaces and it'll use whatever ethernet address goes with it.
>
> In practice, its pretty arbitrary, and often user-configurable independent
> of any ethernet address.  My advice is to always just treat it as an opaque
> value which should be unique.  If a vendor happens to base it on some
> particular ethernet address, I'd treat that as an implementation detail for
> how they achieve uniqueness and not as there being any sort of real
> relationship between the two.
>
> To give a different type of answer:  With Open vSwitch, it defaults to the
> ethernet address of the switch's "local" port with the top 16 bits zeroed
> (this ethernet address being generated at random when last I checked).
>  With Mininet, this generally gets overridden to match the number of the
> Mininet switch.
>
> Hope that helps?
>
> -- Murphy
>
> On Apr 21, 2014, at 10:11 PM, Karthik Sharma <karthik.sharma at gmail.com>
> wrote:
>
> Hi,
>
> When you are creating switches for mininet topology you pass the dpid as
> given below.
>
>
>
>     info( '*** Add switches\n')
>
>     s1 = net.addSwitch('s1', cls=OVSKernelSwitch, dpid='0000000000000201')
>
>     s2 = net.addSwitch('s2', cls=OVSKernelSwitch, dpid='0000000000000202')
>
>     s3 = net.addSwitch('s3', cls=OVSKernelSwitch, dpid='0000000000000203')
>
>     s4 = net.addSwitch('s4', cls=OVSKernelSwitch, dpid='0000000000000204')
>
>     s5 = net.addSwitch('s5', cls=OVSKernelSwitch, dpid='0000000000000205')
>
>     s6 = net.addSwitch('s6', cls=OVSKernelSwitch, dpid='0000000000000206')
>
>
>
> My question is
>
>
>
> What is dpid? How is it related to MAC addresses for each port of the Ethernet
>
> switch.Suppose the switch has 12 ports (for e.g) each of the ports will have a
>
> MAC address.(48 -bits long).How come a switch has a single data path identifier?
>
> How is related to MAC address?
>
>
> Regards,
> Karthik.
>
>
>
>
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>


-- 

With Regards,

Rushit Parekh
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