[Freeswitch-users] Hostname vs IP in SDP

Thu Aug 4 19:35:46 MSD 2016

True, but newer RFCs (6947 for example) are adding extensions such as
"a=altc" which should allow you to advertise both IPv4 and IPv6 support in
an SDP. Having simply a hostname could make that easier. But I see your
point, if the two have to be advertised independently you might as well use
IPs instead of hostnames - there's no clear advantage to be gained one way
or the other.

Best,
Colin

On Thu, Aug 4, 2016 at 11:29 AM Steven Ayre <steveayre at gmail.com> wrote:

> > more and more dual stack endpoint
>
> Bear in mind that the SDP contains 'IN IP4' or 'IN IP6' to pick the IP
> version so you aren't going to be a in position where they can pick at will
> from A and AAAA records for your FQDN.
>
> On 4 August 2016 at 13:25, Colin Morelli <colin.morelli at gmail.com> wrote:
>
>> Hey Steven,
>>
>> I did check that as well. So far as I can tell, most of the shared
>> portions of the SDP come from RFC 4566. The ICE additions in RFC 5245 also
>> claim to allow FQDNs for candidate addresses.
>>
>> My assumption is that it's just not commonly used. But it seems much
>> easier to support hostnames everywhere as more and more dual stack
>> endpoints.
>>
>> Any thoughts on a per-channel advertised address?
>>
>> Best,
>> Colin
>>
>> On Thu, Aug 4, 2016 at 8:14 AM Steven Ayre <steveayre at gmail.com> wrote:
>>
>>> Should point out that although it might be allowed in SDP's RFC that
>>> doesn't necessarily mean it isn't restricted by other WebRTC
>>> specifications. You'll probably want to look into those as well.
>>>
>>> On 4 August 2016 at 12:17, Colin Morelli <colin.morelli at gmail.com>
>>> wrote:
>>>
>>>> Steven,
>>>>
>>>> Thanks for the clarification - that's really helpful (it also means I
>>>> can go file browser bugs which I'll do)
>>>>
>>>> Agreed it'll cause interop issues (for example the ones seen in
>>>> WebRTC). It's too bad, because it could be helpful in a few different
>>>> scenarios.
>>>>
>>>> That said, for now I'm just looking to slowly start using it on devices
>>>> that will have problems with IP addresses. Does anyone know if there's a
>>>> way, via a channel var, to set the advertised address in the SDP?
>>>>
>>>> Best,
>>>> Colin
>>>>
>>>> On Thu, Aug 4, 2016 at 7:03 AM Steven Ayre <steveayre at gmail.com> wrote:
>>>>
>>>>> RFC4566 5. SDP Specification
>>>>> "A session description can contain domain names in the "o=", "u=", "e=",
>>>>> "c=", and "a=" lines."
>>>>>
>>>>> It's a detail I'd expect some implementations may have skipped over
>>>>> though so I'd expect it could lead to interop issues. Also you need to
>>>>> assume it will resolve to the IP you expect, not necessarily the case if it
>>>>> resolves to multiple IPs for example or it has changed and the TTL has not
>>>>> expired yet. And it might not play well with SIP ALGs. I'd avoid it. That's
>>>>> not evidence based, purely gut instinct.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On 3 August 2016 at 06:10, Michael Jerris <mike at jerris.com> wrote:
>>>>>
>>>>>> I have not once in my life seen someone use a hostname instead of an
>>>>>> ip in an sdp, and I do not believe it is legal.
>>>>>>
>>>>>> > On Aug 2, 2016, at 1:00 PM, Colin Morelli <colin.morelli at gmail.com>
>>>>>> wrote:
>>>>>> >
>>>>>> > Hey all,
>>>>>> >
>>>>>> > So it looks like WebRTC has issues dealing with hostnames in the
>>>>>> SDP instead of IP addresses. Particularly, when including a hostname in the
>>>>>> SDP there's no audio in either direction. This is the case in both the
>>>>>> latest Firefox + Chrome browsers.
>>>>>> >
>>>>>> > This is particularly problematic for applications that are WebRTC +
>>>>>> mobile, now that Apple is enforcing applications to support IPv6-only
>>>>>> networks. Using hostnames in the record-route and SDP addresses meets the
>>>>>> requirement since the OS will synthesize an IPv6 address when a DNS query
>>>>>> is performed, but according to the documentation they strongly urge
>>>>>> applications to avoid using address literals in their applications.
>>>>>> >
>>>>>> > Has anyone had success with methods to switch between advertising a
>>>>>> hostname vs IP address in the SDP? Or other methods for solving this
>>>>>> problem?
>>>>>>
>>>>>>
>>>>>>
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