[TICTOC]Re: Enterprise Profile: Support for Non standard TCs

[Doug Arnold <[e-mail]>]

Hello Ron,

For Ethernet - IEEE 802.1Q, I can't remember the RFCs for IPv4 and IPv6 but you can look them up.

Here is the thing. I understand from a network layer model perspective a TC should not change the payload for a frame/packet and just forward it.  However, there is no other way to do a cut-through 1-step TC. I pointed that out to the folks in IEEE 802.1 but they ignored me.  I know for a fact that multiple companies' implementations of TCs do not replace the source address before retransmitting.  I don't blame them.  The standards are preventing a valuable use case just to preserve the purity of their layer model.  I would be surprised if 1588 is the only technology that needs to change message fields on the fly in a cut through switch.

Regards,
Doug
________________________________
From: Ron Cohen <[e-mail]>
Sent: Wednesday, May 22, 2024 2:58 AM
To: Doug Arnold <[e-mail]>; [e-mail] <[e-mail]>
Subject: RE: Enterprise Profile: Support for Non standard TCs


Hi Doug,



TC are not supposed to change source IP address of delay requests.



If the TC is a layer2 switch/bridge, it must not modify the source MAC address while forwarding and must never touch the layer3 addresses.

If the TC is a layer3 IP router, it must not modify the source IP address while forwarding and must change the source MAC address to the MAC address of its egress port.



If the TC is a layer4 device, e.g., a NAT device, it modifies the source IP address of messages as it is its functionality. It may be the case that such functionality is required in the enterprise. My point is that it is far from obvious and the draft needs to elaborate why it’s needed.



>> This is required by the standards that specify the transport networks.

I would appreciate if you point to the relevant standards.



The draft states that additional support is required for this deployment scenario:

“For this deployment scenario timeTransmitters will need to have configured tables of timeReceivers' IP addresses and associated Clock Identities in order to send Delay Responses to the correct PTP Nodes”



These tables would be part of the IEEE1588 spec if this TC behavior was standard. It is not trivial to add support for these tables in HW, if you want to support scale and speed.



Best,

Ron



From: Doug Arnold <[e-mail]>
Sent: Wednesday, May 22, 2024 12:36 AM
To: Ron Cohen <[e-mail]>; [e-mail]
Subject: [EXTERNAL] Re: Enterprise Profile: Support for Non standard TCs



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________________________________

Hello Ron,



Yes.  A TC is required to change the source address of a message at least for Ethernet and IP mappings.  This is not an IEEE 1588 decision.  This is required by the standards that specify the transport networks. Ethernet (IEEE 802.1Q) IPv4 and IPv6.  A TC effectively changes the payload of the messages from the point of view of L2 and L3, so it is a new frame and new packet to those layers.  I think that IPv4 has an option to alter a message in-route, but the node is supposed to zero out the source address.



Regards,

Doug



________________________________

From: Ron Cohen <[e-mail]<mailto:[e-mail]>>
Sent: Tuesday, May 7, 2024 12:43 PM
To: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Subject: [TICTOC]Enterprise Profile: Support for Non standard TCs



Hi,



I’m late to the game here. I apologize in advance if this has already been discussed and decided:



I can’t figure out why the profile needs to support non-standard TCs, or what seems to be a strange combination of a NAT+TC devices:



“In PTP Networks that contain Transparent Clocks, timeTransmitters

   might receive Delay Request messages that no longer contains the IP

   Addresses of the timeReceivers.  This is because Transparent Clocks

   might replace the IP address of Delay Requests with their own IP

   address after updating the Correction Fields.  For this deployment

   scenario timeTransmitters will need to have configured tables of

   timeReceivers' IP addresses and associated Clock Identities in order

   to send Delay Responses to the correct PTP Nodes.”



Is a standard TC allowed to change the source IP address of messages?



There should be a strong reason to require support for such devices in a standard profile.



Best,

Ron



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