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

[Pasi.Eronen (Pasi.Eronen]

Pat Calhoun wrote:
> 
> 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?

How would the WTP know whether the data channel is control+1, or 
found by another SRV lookup?

Something like "If the control channel port in the SRV record 
is 5246, data port is 5247; otherwise, the WTP MUST perform another
SRV lookup" would work, but IMHO it sounds like unnecessary
complexity -- is there any reason why the AC can't just pick 
two consecutive ports?

Best regards,
Pasi