We've been running ipv6 for a year or so now, but some of our newer instances (all on an ESX cluster) are not working. It looks like it's all of our Centos 6 instances. I'm hoping someone can point me in the right direction... tshark indicates that it's neighbor discovery that's failing: <centos666.peak.org> [26] # cat ../network NETWORKING=yes HOSTNAME=centos666.peak.org GATEWAY=207.55.16.1 NETWORKING_IPV6=yes IPV6_AUTOTUNNEL=no IPV6_DEFAULTGW=2607:f678::1 <centos666.peak.org> [27] # cat ifcfg-eth0 DEVICE="eth0" NM_CONTROLLED="no" ONBOOT="yes" TYPE=Ethernet BOOTPROTO=none IPADDR=207.55.16.66 PREFIX=22 GATEWAY=207.55.16.1 DNS1=69.59.192.71 DNS2=69.59.192.72 DOMAIN=peak.org DEFROUTE=yes IPV6INIT=yes NAME="System eth0" IPV6_AUTOCONF=no IPV6ADDR=2607:f678::16:66/64 IPV6_DEFROUTE=yes <centos666.peak.org> [28] # ifconfig eth0 Link encap:Ethernet HWaddr 00:50:56:98:70:8B inet addr:207.55.16.66 Bcast:207.55.19.255 Mask:255.255.252.0 inet6 addr: fe80::250:56ff:fe98:708b/64 Scope:Link inet6 addr: 2607:f678::16:66/64 Scope:Global UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1862 errors:0 dropped:0 overruns:0 frame:0 TX packets:266 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:136703 (133.4 KiB) TX bytes:33944 (33.1 KiB) ipv6 is working locally: <centos666.peak.org> [29] # ping6 2607:f678::16:66 PING 2607:f678::16:66(2607:f678::16:66) 56 data bytes 64 bytes from 2607:f678::16:66: icmp_seq=1 ttl=64 time=0.040 ms 64 bytes from 2607:f678::16:66: icmp_seq=2 ttl=64 time=0.038 ms ^C --- 2607:f678::16:66 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1870ms rtt min/avg/max/mdev = 0.038/0.039/0.040/0.001 ms but not on the lan: <centos666.peak.org> [5] # ping6 2607:f678::1 PING 2607:f678::1(2607:f678::1) 56 data bytes >From 2607:f678::16:66 icmp_seq=2 Destination unreachable: Address unreachable >From 2607:f678::16:66 icmp_seq=3 Destination unreachable: Address unreachable >From 2607:f678::16:66 icmp_seq=4 Destination unreachable: Address unreachable >From 2607:f678::16:66 icmp_seq=6 Destination unreachable: Address unreachable >From 2607:f678::16:66 icmp_seq=7 Destination unreachable: Address unreachable >From 2607:f678::16:66 icmp_seq=8 Destination unreachable: Address unreachable ^C --- 2607:f678::1 ping statistics --- 8 packets transmitted, 0 received, +6 errors, 100% packet loss, time 7892ms tshark for that ping: <centos666.peak.org> [38] # tshark -n -i eth0 ip6 Running as user "root" and group "root". This could be dangerous. Capturing on eth0 0.000000 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation 1.000019 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation 2.000043 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation 4.001030 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation 5.001076 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation 6.001045 2607:f678::16:66 -> ff02::1:ff00:1 ICMPv6 Neighbor solicitation ^C6 packets captured A centos 5.8 vm with the same virtual network connections works fine: <ns6.peak.org> [103] # ping6 2607:f678::1 PING 2607:f678::1(2607:f678::1) 56 data bytes 64 bytes from 2607:f678::1: icmp_seq=0 ttl=64 time=1.34 ms 64 bytes from 2607:f678::1: icmp_seq=1 ttl=64 time=0.894 ms 64 bytes from 2607:f678::1: icmp_seq=2 ttl=64 time=0.871 ms --- 2607:f678::1 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 0.871/1.035/1.342/0.219 ms, pipe 2 <ns6.peak.org> [104] # ping6 ipv6.google.com PING ipv6.google.com(pz-in-x67.1e100.net) 56 data bytes 64 bytes from pz-in-x67.1e100.net: icmp_seq=0 ttl=52 time=14.1 ms 64 bytes from pz-in-x67.1e100.net: icmp_seq=1 ttl=52 time=14.3 ms 64 bytes from pz-in-x67.1e100.net: icmp_seq=2 ttl=52 time=14.3 ms --- ipv6.google.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2001ms rtt min/avg/max/mdev = 14.185/14.296/14.380/0.081 ms, pipe 2 <ns6.peak.org> [489] # tshark -i eth0 -n ip6 Running as user "root" and group "root". This could be dangerous. Capturing on eth0 0.000000 2607:f678::56 -> 2607:f678::1 ICMPv6 Echo request 0.000720 2607:f678::1 -> 2607:f678::56 ICMPv6 Echo reply 1.000990 2607:f678::56 -> 2607:f678::1 ICMPv6 Echo request 1.001759 2607:f678::1 -> 2607:f678::56 ICMPv6 Echo reply 2.001004 2607:f678::56 -> 2607:f678::1 ICMPv6 Echo request 2.001841 2607:f678::1 -> 2607:f678::56 ICMPv6 Echo reply 3.002983 2607:f678::56 -> 2607:f678::1 ICMPv6 Echo request 3.003680 2607:f678::1 -> 2607:f678::56 ICMPv6 Echo reply 4.003991 2607:f678::56 -> 2607:f678::1 ICMPv6 Echo request 4.010478 2607:f678::1 -> 2607:f678::56 ICMPv6 Echo reply 4.650129 2607:f678::1 -> 2607:f678::56 ICMPv6 Neighbor solicitation 4.650171 2607:f678::56 -> 2607:f678::1 ICMPv6 Neighbor advertisement 12 packets captured