Cannot reach one specific IPv6 from one specific network

TwinTurbo@lemmy.world to Selfhosted@lemmy.world – 12 points –

My home ISP does CGNAT for IPv4, but provides native IPv6. I can use IPv6 just fine to access most of my resources, except for one specific server. I can access the server over IPv4 from my home network, and either over v4 or v6 from other networks I've tried. But I can't access it over IPv6 from my home network.

What could be the problem here? Where do I begin to diagnose it

3

Couple questions:

  • What’s your ISP at home?
  • What’s the ISP of the remote IPv6 server?
  • Are the other networks you’ve tried from the same or different?

I’d start with traceroute and see how far your IPv6 traffic gets before it fails. It could very well be some peering or routing issue between some of the ISPs in between you and wherever that IPv6 address lives. If this ends up identifying where the traffic dies, a lot of the tier 1 ISPs have BGP looking glass servers so you can get an idea of what they know about that subnet.

I've tried from networks outside my home and I can access the server from there. Looking at a traceroute, I stop getting anything somewhere between my ISP and the datacenter the server is in.

You should be able to look up the last hop that responds (via ARIN or whoever the internet number agency is in your region) and see who that ISP is. Now the annoying part is some ISPs just drop ICMP at their border so it’s not s smoking gun that they are the issue.