asterisk users - Aug 2011 - Possibly odd sip.conf security requirements. Possible?

Hi,

Is the following possible in some way? I want to have several SIP
providers able to send me calls, each provider may send calls into
many possible DDIs. Each provider has a cluster of servers, but is
unable to authenticate with me, so the following would be a sort of
pseudo-code sip.conf example.


[general]
context = barred  ; Unknown/other source of calls

[provider 1]
type = peer
context = provider1-context   ; deal with provider's calls 1
deny = 0.0.0.0/0.0.0.0
permit = 12.13.14.0/24  ; This provider has servers in this range

[provider 2]
type = peer
context = provider2-context   ; deal with provider's calls 2
deny = 0.0.0.0/0.0.0.0
permit = 22.23.24.0/24  ; This provider has servers in this range

[provider 3]
type = peer
context = provider3-context   ; deal with provider's calls 3
deny = 0.0.0.0/0.0.0.0
permit = 32.33.34.0/24  ; This provider has servers in this range


Normally a call into SIP has one of 3 paths:
1) Unauthenticated, so use the default
2) Identifiable username
3) Identifiable IP address

In the above example, we have a BLOCK of IP addresses instead of a
single address. Can this be made to work?

Thanks for any pointers.

Regards,
Steve