Trying to figure out what the heck is going on here. Any good explanations cheerfully accepted. Background: Home internet router is a Linksys WRT1200AC that had been running OpenWRT 15.05.01. IPv6 worked just fine - Comcast handed me a /60 via DHCP-PD and no issues. I reflashed it to Lede 17.01, and after doing all the reconfig, I'm hitting a really strange IPv6 issue. Symptoms - IPv6 still configures correctly, but IPv6 packets appear to go out and disappear into the ether when they leave the Linksys. Doing a traceroute to any IPv6 destination makes things work again - for a while (from 15 minutes to an hour or two). As seen from my laptop (I have the matching tcpdump from the outbound interface on the Linksys): [~] ping -6 -c 3 listserv.vt.edu PING listserv.vt.edu(listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769)) 56 data bytes --- listserv.vt.edu ping statistics --- 3 packets transmitted, 0 received, 100% packet loss, time 2070ms [~] traceroute -6 listserv.vt.edu traceroute to listserv.vt.edu (2001:468:c80:2105:211:43ff:feda:d769), 30 hops max, 80 byte packets 1 2601:5c0:c001:69e2::1 (2601:5c0:c001:69e2::1) 2.417 ms 3.077 ms 5.358 ms 2 * * * 3 * * * 4 * * * 5 * * * 6 * hu-0-10-0-7-pe04.ashburn.va.ibone.comcast.net (2001:558:0:f5c1::2) 31.478 ms 31.975 ms 7 2001:559::d16 (2001:559::d16) 32.406 ms 17.102 ms 24.751 ms 8 2001:550:2:2f::a (2001:550:2:2f::a) 23.245 ms 23.519 ms 22.185 ms 9 2607:b400:f0:2003::f0 (2607:b400:f0:2003::f0) 29.782 ms 28.604 ms 29.891 ms 10 2607:b400:90:ff05::f1 (2607:b400:90:ff05::f1) 30.423 ms * 30.680 ms 11 * * * 12 listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769) 34.562 ms 39.072 ms 24.633 ms [~] ping -6 -c 3 listserv.vt.edu PING listserv.vt.edu(listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769)) 56 data bytes 64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=1 ttl=53 time=33.3 ms 64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=2 ttl=53 time=24.3 ms 64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=3 ttl=53 time=46.0 ms --- listserv.vt.edu ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2003ms rtt min/avg/max/mdev = 24.334/34.595/46.093/8.927 ms So it looks like something times out somewhere and fails to pass packets back. TCP connections don't keep IPv6 alive. I have a browser window that auto-updates every 5 minutes, and a SmokePing process on a Raspberri Pi uploads to a server at work every few minutes, and those eventually drop back to IPv4 when the IPv6 TCP fails to connect. And normal UDP doesn't seem to keep it alive - NTP pointing at IPv6 peers loses connectivity as well. But a traceroute wakes it up. It's almost like some router is losing the route to me out of the FIB, and fixes it when it has to handle a packet on the CPU slow path (like send back a 'time exceeded'). But I'm mystified why this started when I reflashed my router.