Re: actpass redux

Hi All,

There was a discussion regarding the setup attribute value in subsequent
offers when establishing new DTLS association is not desired. Based on that
discussion it was decided that setup value can be either currently
negotiated value or actpass. There are also UDP/DTLS without STUN NAT
traversal scenarios that only work when end point behind NAT is active. I
think sending actpass in offers is a generally safer option, but I think
SHOULD here is more appropriate then MUST.

Please note that https://tools.ietf.org/html/rfc5763#section-5 says:

The endpoint MUST use the setup attribute defined in [RFC4145]. The
endpoint that is the offerer MUST use the setup attribute value of
setup:actpass and be prepared to receive a client_hello before it receives
the answer.


This applies not only to initial but to ALL offers.

Finally, I can double check, but I am fairly sure there are current
implementation that violate this rule.

Regards,

_____________
Roman Shpount

On Fri, Jun 2, 2017 at 12:44 PM, Eric Rescorla <[email protected]> wrote:

> Hi folks,
>
> RFC 5763 required (and JSEP imported) that all offers include
>
>   a=setup:actpass
>
> However, assuming I am reading:
>   https://tools.ietf.org/html/draft-ietf-mmusic-dtls-sdp-24
>
> correctly, S 4.2 allows the initial offer to contain anything,
> though encourages actpass:
>
>    When an offerer sends the initial offer, the offerer MUST insert an
>    SDP 'setup' attribute according to the procedures in [RFC4145], and
>    one or more SDP 'fingerprint' attributes according to the procedures
>    in [RFC8122].  In addition, the offerer MUST insert in the offer an
>    SDP 'tls-id' attribute with a unique value.
>
>    If the offerer inserts the SDP 'setup' attribute with an 'actpass' or
>    'passive' attribute value, the offerer MUST be prepared to receive a
>    DTLS ClientHello message (if a new DTLS association is established by
>    the answerer) from the answerer before the offerer receives the SDP
>    answer.
>
> For subequent offers, it also gives flexibility but points at 4145.
>
>
> So...
>
> 1. Changing the behavior for initial offers seems like it presents
> a serious interop risk, because previously you could depend on
> the offer being actpass.
>
> 2. JSEP requires actpass for all offers, so at least it's stricter.
>
>
> What was the rationale for these changes? Feel free to point me at the
> mailing list discussion where that happened.
>
> -Ekr
>  Hi folks,
>
> RFC 5763 required (and JSEP imported) that all offers include
>
>   a=setup:actpass
>
> However, assuming I am reading:
>   https://tools.ietf.org/html/draft-ietf-mmusic-dtls-sdp-24
>
> correctly, S 4.2 allows the initial offer to contain anything,
> though encourages actpass:
>
>    When an offerer sends the initial offer, the offerer MUST insert an
>    SDP 'setup' attribute according to the procedures in [RFC4145], and
>    one or more SDP 'fingerprint' attributes according to the procedures
>    in [RFC8122].  In addition, the offerer MUST insert in the offer an
>    SDP 'tls-id' attribute with a unique value.
>
>    If the offerer inserts the SDP 'setup' attribute with an 'actpass' or
>    'passive' attribute value, the offerer MUST be prepared to receive a
>    DTLS ClientHello message (if a new DTLS association is established by
>    the answerer) from the answerer before the offerer receives the SDP
>    answer.
>
> For subequent offers, it also gives flexibility but points at 4145.
>
>
> So...
>
> 1. Changing the behavior for initial offers seems like it presents
> a serious interop risk, because previously you could depend on
> the offer being actpass.
>
> 2. JSEP requires actpass for all offers, so at least it's stricter.
>
>
> What was the rationale for these changes? Feel free to point me at the
> mailing list discussion where that happened.
>
> -Ekr
>
>
> _______________________________________________
> mmusic mailing list
> [email protected]
> https://www.ietf.org/mailman/listinfo/mmusic
>
>

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