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

[Pasi.Eronen (Pasi.Eronen]

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
>