# Reserved identifiers for diagnostic and debugging tools

**URL:** <https://forum.opencyphal.org/t/reserved-identifiers-for-diagnostic-and-debugging-tools/1833>\
**Category:** Specification\
**Created:** [February 27, 2023, 10:55pm UTC](https://forum.opencyphal.org/t/reserved-identifiers-for-diagnostic-and-debugging-tools/1833 "2023-02-27T22:55:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![scottdixon](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/scottdixon/32/39_2.png) [@scottdixon](https://forum.opencyphal.org/u/scottdixon)\
**Post date:** [February 27, 2023, 10:55pm UTC](https://forum.opencyphal.org/t/reserved-identifiers-for-diagnostic-and-debugging-tools/1833/1 "2023-02-27T22:55:03Z")

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Section 5.2.1 of the Cyphal specification reads:

> …  
> The two uppermost node-ID values are reserved for diagnostic and debugging tools; these node-ID values  
> should not be used in fielded systems.

This seems to create a wart for a mixed system using both CAN and UDP where the spec reserves node identifiers 126 and 127 on CAN but 65534 and 65535 on UDP (etc). Perhaps we should reword this to be fixed to 126 and 127 regardless of protocol since:

> Valid values of node-ID range from 0 up to a transport-specific upper boundary which is guaranteed to be  
> above 127 for any transport.

Proposed new text is then:

> …  
> Node-ID values 126 and 127 are reserved for diagnostic and debugging tools; these node-ID values  
> should not be used in fielded systems.

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<div class="post-metadata">

**Author:** ![pavel.kirienko](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/pavel.kirienko/32/9_2.png) [@pavel.kirienko](https://forum.opencyphal.org/u/pavel.kirienko)\
**Post date:** [February 28, 2023, 12:45am UTC](https://forum.opencyphal.org/t/reserved-identifiers-for-diagnostic-and-debugging-tools/1833/2 "2023-02-28T00:45:07Z")

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+1.