Bill,Carrier grade NAT means you aren't issued a Public IP on the WAN interface facing your ISP. There's a block of IP space (100.64.0.0/10) used for this purpose. CG NAT exists because of exhaustion of the Global IPv4 space.Yes, this would mean you cannot control receipt of protocols like: TCP, UDP and importantly for AMPR - IP Protocol No. 4.It sounds like they may have recently implemented this on their customer network. The ISP can offer their own services because they use their Public IP space on those needed servers. Another example where they use Global IPs - is on the CG NAT router that connects you to the Internet.It's possible they now offer a Public IP as an added service. You could inquire about that.73,LynwoodKB3VWG  -------- Original message --------From: Harold Kinchelow via 44net <44net(a)mailman.ampr.org> Date: 10/4/22 22:32 (GMT-05:00) To: 44net(a)mailman.ampr.org Subject: [44net] New ISP blocking VoIP I am reposting this for William Horne because he post using a prevous message of mine but it came directly to me.  Please take a look @ his issue below. Thanks Harold K7ILO From: E. William Horne <malassimilation(a)gmail.com> Sent: Sunday, October 2, 2022 2:57 PM To: Harold Kinchelow <k7ilo(a)outlook.com> Subject: New ISP blocking VoIP   OM, I humbly request that you help me in any way you can to get around my new ISP blocking  VoIP phone calls. On 9/4/2022, they stopped without warning or justification: both Callcentric and Hamshack Hotline went dead at the same time. On Monday, 9/5, I complained to the "Tech Support" number, and I listened to their employee being told to "Blame it on his router," and then to her doing so. I told her that wouldn't cut it, and she said she would "reset my modem" and then Callcentric came back online. I made a call with my Cisco SIP phone, and talked to my brother-in-law in Massachusetts for a few minutes, but right after we hanged up, the Callcentric line was dead again. I complained again, with nothing but gobbledygook and shaming and finger-pointing to show for it. The ISP had some flack call me, and he told me that they were doing "Cee-Gee-NAT," and couldn't map the ports required for Voip. I asked him how the ISP could offer it's own VoIP service, right on their public-facing website, if that were so. He said he'd have to do some more research, and I've never heard back. Here's a fervent "TIA" for any help you can offer. 73, Bill Horne, W4EWH 828-380-1440 (Cell)