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

[Christer Holmberg <[e-mail]>]

Hi,

    >> 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.
    >
    > There are two cases here: 0, and > 255.  The latter would be a syntax error for this option; the option description clearly limits the value to 
    > a single byte (Table 1).  Zero is not a syntax error, but a value that the authors chose to disallow.
    >
    >> 	• 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.
    >
    > A syntax error or a disallowed value in a request is a client error, no?

    The client may have included a valid value, but due to too many hops it reached 0. That is not a client error in my opinion.

    Sure, if the value is larger than 255 I guess 4.00 would be ok, because that is a protocol violation.

    >> 	• Based on my experience in SIP, it is VERY useful to have a dedicated response code for this (SIP defines ‘483 Too Many Hops’).
    >
    > We do have one for this case: TBA1 | Hop Limit Reached
    > But this is different from a syntax error.

    Yes, I noticed that (and just sent a reply about it).

    But, again, if the value reaches 0, shouldn't TBA1 be used instead of 4.00? 

    >> 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.
    >
    > Specific response codes are useful if you want specific state machine transitions to happen

    Specific response codes are also very useful for debugging - especially in this case where one probably should start by looking at the network/routing configurations instead of the endpoint implementations.

Regards,

Christer