IPv6 IP lookup trouble
i'm trying to get a reliable public ipv6 for my server instances using a custom ip lookup script. it works for ipv4 addresses, but i'm hitting a wall with ipv6.
specifically, i'm seeing inconsistent behavior where some ipv6 endpoints just timeout or return connection refused, even when direct ping works. is there some common gotcha i'm missing?
here's a snippet of the console output:
curl -6 ifconfig.co
curl: (7) Couldn't connect to server
# (or similar timeout/refused error)help a brother out please...
1 Answers
MD Alamgir Hossain Nahid
Answered 35 seconds agoHello Diya Singh,
I've definitely run into this exact type of IPv6 connectivity headache myself, and it can be incredibly frustrating when you're trying to nail down reliable IP resolution for your server instances. First off, just a quick heads-up on your 'i'm trying' โ a capital 'I' always feels a bit more assertive when you're wrestling with network issues, right?
The core issue here is often not with the `curl` command itself, but with the underlying network configuration or firewall rules. When `ping` works but `curl` (which uses TCP) fails with timeout or connection refused, it strongly suggests that ICMP traffic (used by ping) is allowed, but TCP traffic on port 80/443 (used by curl) is being blocked or routed incorrectly. Common culprits include:
- Local Firewall: Your server's local firewall (e.g., `ufw`, `firewalld`, `iptables`) might be configured to allow IPv4 but not explicitly IPv6 for outgoing connections, or it might be blocking the response traffic. Check your `ip6tables -L` or `ufw status verbose` output.
- Upstream Firewall/Security Group: If your server is hosted with a cloud provider, their security groups or network ACLs might be configured to allow IPv4 outbound/inbound but not IPv6. Double-check these settings.
- IPv6 Routing Issues: While less common if ping works, there could be specific routing table entries missing or incorrect for TCP over IPv6 that don't affect ICMP. Verify your `ip -6 route` output.
- Target Service: Although `ifconfig.co` is generally reliable, try an alternative IPv6 lookup service like `curl -6 ipv6.icanhazip.com` or `curl -6 api6.ipify.org` to rule out an issue with the specific endpoint you're querying.
Are your server instances behind any kind of cloud-provider-managed firewall or NAT64 setup?