How to set up NAT in mikrotik with IP spoofing?

Question

SIP

The Big Three operator provides a SIP stream but allows connection to its server only from one of its IP addresses, how to set up NAT on a router when connecting to a SIP telephony server so that the source IP addresses are “substituted” for the given address and everything looks legitimate. NAT needs to be configured between the SIP interface and the local interface looking in my direction.
For the life of me, I’m confused in three pines, I can’t configure it, it won’t let me in .... the SIP
scheme, the

operator wants to see that they go to him from the IP address 1.1.1.2
How I did the sword, I send traffic through the gateway

Answer 1

You twist normal NAT.
SIP clients send their IPs in signaling messages.
The operator may not like exactly what is inside.

Answer 2

Here you don’t need to configure Mikrotik, but understand how to get an IP that the operator likes. We sit down and draw a connection diagram.

Answer 3

0) do you have sip - is it a separate 3rd wire, or does one of the first two additionally give sip? Are the ISPs tagged (reserve/balancing)?
1) why do you have eth9 in the picture - it's in and not out interface?
2) did mark-routing, and mark-packet based on mark-routing?
3) have you done:
- add 1.1.1.2 to eth9
- add route 1.1.1.2/24 (or what mask did sip-prover give you?) through 1.1.1.1
- add route 10.0.0.2/? through 1.1.1.2 with the required marking

Answer 4

strangely, the IP from ISP3 should be substituted (that is, the IP issued by the SIP provider)