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

[Kevin P. Fleming]

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
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