Re: [asterisk-biz] OT Preventing VoipSpam Was RE: [OT] Reporting Spam

On Nov 7, 2008, at 7:48 AM, Alexander Lopez wrote:

> Would a system such as SPF or DomainKeys work for Voip calls.
>
> It is beneficial to have your SIP PBX accept guest calls but it
> would be
> nice if those guest calls could be validated somehow as a legitimate
> call without having to use something like Zapateller oops I mean,
> Dahadi-teller???

It would be possible right now to create a filter mechanism that would
allow you to whitelist/blacklist callers based on "Caller ID" in the
From: header, using existing DNS tools with probably very few
downsides. It's like SPF (or RPF, if you're a router geek) in some
ways, but uses SRV records or A records to determine if the call is
'valid' as an origin. It doesn't talk at all about creating the
whitelist/blacklist, only about how you verify that the From: header
(or other header) is originating from an IP address that is authorized
to send it.

Check out this proposal I did a while ago:

https://mail.internet2.edu/wws/arc/sip.edu/2006-07/msg00012.html

and a version of the Asterisk AGI script that's a little less mangled:

http://forum.e164.org/index.php?topic=16.0

JT

---
John Todd
jtodd@digium.com +1-256-428-6083
Asterisk Open Source Community Director

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