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[core] A couple of late comments on Hop-Limit

Christer Holmberg <christer.holmberg@ericsson.com> Wed, 16 October 2019 10:13 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: "core@ietf.org" <core@ietf.org>
Thread-Topic: A couple of late comments on Hop-Limit
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Date: Wed, 16 Oct 2019 10:13:24 +0000
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Subject: [core] A couple of late comments on Hop-Limit
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Hi,

I haven’t followed the hop-limit discussions, so I apologize if the following has already been discussed. I also know that my comments come very late in the process, so sorry for that.

Adam may have an opinion regarding Q2.


Q1:

The draft talks about “CoAP messages”. But, if I understand correctly, it is only intended to be used for CoAP request messages, right?


  *   Since you use a CoAP option, the mechanism can’t be used in an empty message.
  *   I assume you don’t want to use the mechanism when sending a response, because then there is a risk that the client will not receive it.

Unless I’ve missed it, I think it should be more explicit what the applicability of the mechanism is.


Q2:

The draft says that a CoAP message with the Hop-Limit option value set to 0 bigger than 255 must be rejected with a 4.00 Bad Request response.


  *   Is 4.00 really an appropriate response code? When reading the HTTP definition for 400 Bad Request (CoAP inherits the semantics), it is about a client error (miss formed message, etc), which is not the case here.
  *   Based on my experience in SIP, it is VERY useful to have a dedicated response code for this (SIP defines ‘483 Too Many Hops’). Because, when this happens, it is often related to *network configuration and/or routing issues* – not to client implementation issues – so it is VERY useful information when trying to figure out why the message was rejected.

Regards,

Christer

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