Posted on June 1, 2021 8:16 am
 |  Asked by Lasse Johnsen
 |  108 views
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Hello,

I am interested in ptp transparent clock operation on the 7150S switch. I have configured:

ptp mode e2etransparent

…..

interface Ethernet3

switchport access vlan 10

ptp enable

!

interface Ethernet4

switchport access vlan 10

ptp enable

!

On one port I have a PTP clock, on the other a PTP client.

I can see the counter incrementing:

– show ptp interface counters

Interface Ethernet3

Sync messages sent: 0

Sync messages received: 10372

Follow up messages received: 10370

Delay request messages sent: 10370

Delay request messages received: 0

Delay response messages sent: 0

Delay response messages received: 10371

Interface Ethernet4

Sync messages sent: 10370

Sync messages received: 0

Follow up messages sent: 10370

Follow up messages received: 0

Delay request messages sent: 0

Delay request messages received: 10371

Delay response messages sent: 10371

Delay response messages received: 0

I’ve reviewed this:

https://www.arista.com/en/um-eos/eos-precision-time-protocol-ptp-commands

and this:

https://www.arista.com/assets/data/pdf/Whitepapers/Technical_Solution_Guide___Precision_Time_Protocol.pdf

In the first reference it says:

“e2etransparent: The device acts as an end-to-end transparent clock, synchronizing all ports to a connected master clock and updating the time interval field of forwarded PTP packets using switch residence time.”

…. so I don’t really know what that means. In PTP terms, that’s nonsense. There is no “time interval field” (there is a logMessageInterval field which a transparent clock should not touch), but I am going to assume what is inferred is the correctionField as defined in IEEE1588-2008 section 13.3.2.7.

Now I don’t know if the Arista is a one-step or two-step transparent clock and I don’t really care, but my observation is that on no packet exchanged between the clock and the client through the switch is the correction field any other value than 0.

Does this feature work in the 7150S – can it act as a transparent clock? for unicast? for multicast? (it should do both)

Hardware DCS-7150S-24-CL-R. Software 4.23.7.1M

All the best,

Lasse

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Posted by Sarthak P Shetty
Answered on June 2, 2021 11:18 pm

Hi Lasse,

Hope you are well.
By default, we will act as two step transparent clock here. And you are right in assuming that the correction field is updated by the TC.
To answer your other questions, we will need a few more details and ultimately it will also be better to take a look at your setup.
Would you mind sending an email to support@arista.com?
This will open a case and it will be easier for correspondence with us. It will also be easier for us to involve appropriate folks to get all questions answered.

 

Thanks,
Sarthak (East Coast TAC)

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Posted by Sarthak P Shetty
Answered on June 9, 2021 8:44 pm

Hi Lasse,

Hope you are doing well. Just to close the loop on this thread, your questions were answered after some discussions with Arista on a different channel where some configuration tuning assisted in achieving desired results. At this point do let us know if you have any outstanding questions, otherwise we can go ahead and mark this thread as resolved.

Thanks,
Sarthak (East Coast TAC)

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