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<@1145576664366055464>  Hi,

I have my PBX connected to Retell, and I was wondering whether you provide a fixed list of IP addresses that Retell uses to connect to my PBX.

If so, could you share those IPs so I can whitelist them and block all other traffic?

Or are the IP addresses dynamic, making this kind of restriction impossible?

Thanks!

Thanks for tagging me <@612572507345649664>. I'll look through relevant sources and get back to you shortly.

### Answer
 Retell provides fixed IP blocks that you can whitelist for your PBX connection. [(1) ](<https://docs.retellai.com/deploy/custom-telephony>)

The IP ranges are: 
- `18.98.16.120/30` (All regions) 
- `143.223.88.0/21` (Certain United States traffic) 
- `161.115.160.0/19` (Certain United States traffic) 

You can use these IP blocks to whitelist traffic to Retell's SIP server. This allows you to restrict your PBX to only accept connections from Retell's infrastructure.

Feel free to tag <@1145576664366055464> with additional questions. I also appreciate feedback, it helps me improve.

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To learn more, see the sources I considered:

[[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony)
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