[Serusers] Loose Routing ramifications

[justiceguy at pobox.com]

Hello list,

I am new to SER and trying to understand the ramifications and 
downsides of SIP Loose Routing versus Strict.  I have read RFC3261 
and some net documentation, but I'm still having trouble seeing 
the big picture.  In particular, we are testing a SIP route to an 
ITSP, and they have specified to us "no SIP loose routing".  I'm 
trying to understand, why do providers do this?  What is the 
downside?  What are Industry Best Practices?

We have some downstream customers that might be connecting 
Asterisk IAX to us, and then we will be routing these calls via 
SIP to the ITSP provider.  It seems to me that there might be 
ramifications for loose versus strict routing in how we process 
these calls.

Can anyone with SIP routing experience explain best practices or 
Advantages/Disadvantages, or point me to a link?

I found a document that explains the 'problem' with Strict 
routing:

“Strict” routing (Route/Record-Route as defined in bis-05 and 
before) was too strict. Service logic could not affect routing of 
the initial request.

* Strict routing conflates the request target with the next hop 
destination.

* Strict route processing throws away the information in the 
received Request-URI.

* Behavior of UAs with default-outbound-proxies problematic.

* Brittle system failure if any element misroutes.

TIA,
Jason Ostrom