[asterisk-users] chan_sip sending from wrong source address when multiple interfaces are used

[Jeff LaCoursiere]

On Thu, 2012-07-12 at 15:49 +1200, Alec Davis wrote:
> I've seen similar.
> 
> We tried 4 interfaces. On 4 lans, are these considered to be overlapping?
> 192.168.1.1
> 192.168.2.1
> 192.168.3.1
> 192.168.4.1
> 

Depends on the netmask you use :)  Assuming you used /24, so "no", they
don't overlap.

This does exhibit the problem though.  Your OS stack assumes one of
those addresses - the first identified interface? - is the one that all
replies will appear to come from.  So phones on the 192.168.2.0/24
network that try to register get replies from 192.168.1.1 and ignore
them.


j

> I tried this months ago on 1.8, and set provisioned phones to register with
> asterisk interface on the lan they were on.
> The phones won't register, we're un-responsive, 60 of them.
> 
> Removed the bindings, and left only one.
> Reprovisioned the phones again, all 60 of them. All is well.
> 
> Have I tried again. No.
> Did I have enough time to debug. No.
> Sorry.
> 
> Alec Davis
>  
> 
> > -----Original Message-----
> > From: asterisk-users-bounces at lists.digium.com 
> > [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of 
> > Kevin P. Fleming
> > Sent: Thursday, 12 July 2012 2:28 a.m.
> > To: asterisk-users at lists.digium.com
> > Subject: Re: [asterisk-users] chan_sip sending from wrong 
> > source address when multiple interfaces are used
> > 
> > On 07/11/2012 07:51 AM, Olle E. Johansson wrote:
> > >
> > > 10 jul 2012 kl. 20:50 skrev Kevin P. Fleming:
> > >
> > >> On 07/10/2012 03:24 AM, Olle E. Johansson wrote:
> > >>
> > >>> The Asterisk SIP channel has no knowledge about 
> > interfaces and can't 
> > >>> bind to a specific interface for communication. In fact, 
> > it's a well 
> > >>> known bug that if you have multiple interfaces with different IP 
> > >>> networks, Asterisk will send from the wrong IP on some of 
> > the interfaces.
> > >>
> > >> Are you sure about that? The only problem area that I'm 
> > aware of is when there are multiple *overlapping* interfaces 
> > (on the same subnet, or providing the same route(s)). In that 
> > case, Asterisk can receive messages on one IP address out of 
> > the overlapping set, but reply using a different one from the 
> > set, because it doesn't specify the source IP address and 
> > instead lets the UDP/IP stack select one.
> > >>
> > >> If the interfaces don't overlap in any way, I don't see 
> > how it would be possible for Asterisk to send messages with 
> > the wrong source IP address, since it does not specify the 
> > source IP address at all. If this is occurring, it must 
> > involve the operating system's IP stack in some fashion.
> > >
> > > Yes, I still use quite a lot of IPtables tricks to overcome 
> > this issue.
> > 
> > That's quite interesting; can you describe a scenario where 
> > this occurs?
> > 
> > --
> > Kevin P. Fleming
> > Digium, Inc. | Director of Software Technologies
> > Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | 
> > Skype: kpfleming
> > 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA Check us 
> > out at www.digium.com & www.asterisk.org
> > 
> > 
> > 
> > --
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