Capwap Mailing List: Re: Issue 156: Need more details on use of DNS for discovery

[Pat Calhoun (pacalhou) (pcalhoun]

The IANA service name has already been taken care of, and is already in
the IANA Considerations section in -12 (as requested during WG LC). I
do, however, have an issue with the last sentence in Pasi's proposed
text, as it states that data channel is control+1. However, in the
previous sentence he clearly states that control MAY NOT be the default
(assigned) port. So I would prefer to change the last sentence to:

"Note that the SRV record MAY specify a non-default port number for the
control channel; the default port number for the data channel is the
next port number (control channel port + 1). However, in the case where
the control channel uses a non-default port number, the WTP MAY perform
a SRV lookup with Service name "capwap-data" and Proto "udp". Thus, the
name resolved in DNS would be e.g., "_capwap-data._udp.example.com"."

Comments?

PatC 

-----Original Message-----
From: Margaret Wasserman [mailto:margaret [at] thingmagic.com] 
Sent: Thursday, August 07, 2008 5:43 AM
To: Pasi.Eronen [at] nokia.com
Cc: Pat Calhoun (pacalhou); capwap [at] frascone.com
Subject: Re: [Capwap] Issue 156: Need more details on use of DNS for
discovery

FWIW, Pasi's wording sounds good to me.  I also agree that we should ask
for an IANA-assigned service name, which implies a related change to the
IANA Considerations.

Margaret

On Aug 7, 2008, at 5:27 AM, <Pasi.Eronen [at] nokia.com>
<Pasi.Eronen [at] nokia.com> wrote:

> Hi Pat,
>
> The 'DNS name "CAPWAP-AC-Address" MAY be resolvable' part still isn't 
> quite right; that DNS name won't be resolvable (which is clear after 
> reading the third sentence). Also, some more details would be helpful 
> for the SRV record part. Would something like this match your intent?
>
>   DNS: The WTP MAY support use of DNS SRV records [RFC2782] to
>   discover the AC address(es).  In this case, the WTP first obtains
>   (e.g., from local configuration) the correct domain name suffix
>   (e.g., "example.com") and performs a SRV lookup with Service name
>   "capwap-control" and Proto "udp". Thus, the name resolved in DNS
>   would be, e.g., "_capwap-control._udp.example.com".  Note that the
>   SRV record MAY specify a non-default port number for the control
>   channel; the port number for the data channel is the next
>   port number (control channel port + 1).
>
> (I'm assuming the use of the IANA-assigned service name, instead of 
> non-registered "CAPWAP-AC-Address"; and with this text about SRV port 
> number handling, you might need small tweaking in Section 3.1, too.
> Or you might want to handle port number in some other way.)
>
> Best regards,
> Pasi
>
>> -----Original Message-----
>> From: ext Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com]
>> Sent: 31 July, 2008 01:38
>> To: Eronen Pasi (Nokia-NRC/Helsinki); capwap [at] frascone.com
>> Subject: RE: Issue 156: Need more details on use of DNS for discovery
>>
>> My apologies, Pasi. I'm not sure what I was thinking when I wrote the

>> text.
>>
>> What I should have sent was:
>>
>> <text>
>>    DNS:  The DNS name "CAPWAP-AC-Address" MAY be resolvable to one or
>>       more AC addresses.  A WTP that wishes to make use of DNS SHOULD
>>       use the format described in [RFC2782].  The recommended format 
>> for
>>       a lookup would be CAPWAP-AC-Address._udp.example.com.
>> </text>
>>
>> Does that make more sense?
>>
>> PatC
>>
>> -----Original Message-----
>> From: Pasi.Eronen [at] nokia.com [mailto:Pasi.Eronen [at] nokia.com]
>> Sent: Wednesday, July 30, 2008 12:29 PM
>> To: Pat Calhoun (pacalhou); capwap [at] frascone.com
>> Subject: RE: Issue 156: Need more details on use of DNS for discovery
>>
>> Pat Calhoun wrote:
>>>
>>> Pasi's comment was:
>>>
>>>    Section 3.3: there's a single sentence about DNS-based discovery;
>>>    probably slightly more details would be useful.
>>>
>>> Well... There's not much else we can say, but I am proposing the 
>>> following text In hopes that it will provide more clarity to the 
>>> implementor.
>>>
>>> <new text>
>>> 3.3.  AC Discovery
>>> [...]
>>>       DNS: The DNS name "CAPWAP-AC-Address" MAY be resolvable to one
>>>       or more AC addresses.  A WTP that wishes to make use of DNS
>>>       SHOULD use the format described in [RFC2782].  The
>> recommended
>>>       format for a lookup would be _capwap._udp.example.com.
>>> </new text>
>>
>> I have some trouble parsing the 'The DNS name "CAPWAP-AC-Address" MAY

>> be resolvable...' part. It seems to be suggesting doing a DNS query 
>> for DNS name "CAPWAP-AC-Address" -- or in other words, defining a new

>> Top-Level Domain. That probably isn't a good idea.
>>
>> The two latter sentences are also leaving awfully lot of details to 
>> the implementor -- RFC2782 has specific requirements about the labels

>> etc.
>> (E.g. RFC 3861 has much more text about using SRV records for another
>> purpose.)
>>
>> Best regards,
>> Pasi
>>
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