Hands-on commands to verify and troubleshoot IPv6 reachability from the shell. 16.11.2025 | reading time: 3 min Want to know if your host can reach the IPv6 internet? Run a few simple commands and read the answers: this short guide shows which checks to run and how to interpret their output. Try a quick ICMP probe Do it now: run an ICMP probe to a public IPv6 address to confirm basic reachability, for example: ```bash $ ping6 -c 3 2001:4860:4860::8888 PING 2001:4860:4860::8888(2001:4860:4860::8888) 56 data bytes 64 bytes from 2001:4860:4860::8888: icmp_seq=1 ttl=115 time=12.3 ms 64 bytes from 2001:4860:4860::8888: icmp_seq=2 ttl=115 time=13.1 ms 64 bytes from 2001:4860:4860::8888: icmp_seq=3 ttl=115 time=12.8 ms --- 2001:4860:4860::8888 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2002ms rtt min/avg/max/mdev = 12.342/12.768/13.142/0.401 ms ``` If that succeeds you have ICMPv6 reachability; next, test TCP/HTTP over IPv6 with `curl -6` to exercise application-layer connectivity and DNSv6 resolution. Inspect local configuration When probes fail, check the host configuration: run `ip -6 addr` to see IPv6 addresses and `ip -6 route` to confirm routes; use `sysctl net.ipv6.conf.all.disable_ipv6` to verify IPv6 is enabled; if an address is missing, inspect RA/DHCPv6 on the network or the NIC driver. Simulate a TCP connection Test a TCP handshake to a remote IPv6 server to rule out ICMP filtering: use `curl -6 -I https://[2606:4700:4700::1111]/` or a raw TCP check with `nc -6` to a known service port; a successful TCP SYN/ACK proves end-to-end IPv6 for TCP. Common failure modes and remedies Packets drop if the ISP or upstream router does not route IPv6, if firewall rules block ICMPv6 neighbor discovery or if NAT64/DNS64 is misconfigured; check router advertisements, firewall rules for ICMPv6 types 133/134/135/136, and confirm DNS returns AAAA records when expected. Related verification commands For path and latency troubleshooting use `tracepath -6` or `traceroute -6`; for DNS lookups use `dig AAAA` or `getent ahosts`; and capture packets with `tcpdump -i any ip6` to see neighbor discovery and ICMPv6 traffic. Next steps Having validated reachability, automate checks in a script or monitoring system and log failures so you spot regressions quickly; keep practicing these commands to build reliable IPv6 troubleshooting habits and deepen Linux network skills. Join Bits & Bytes Academy First class LINUX exam preparation. network troubleshooting utilities
