Hi, I have an issue with what seems like a trivial ipv6 configuration. interface FastEthernet0/48 description cocytus no switchport ip address 10.0.9.42 255.255.255.252 load-interval 30 ipv6 address 2001:4830:1252::1/64 ipv6 enable no cdp enable end -=[~]=- -=[Thu Feb 05]=- -=[01:32:30]=- [root@cocytus]# ifconfig vr3 vr3: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 lladdr 00:00:24:c8:e1:07 groups: egress media: Ethernet autoselect (100baseTX full-duplex) status: active inet 10.0.9.41 netmask 0xfffffffc broadcast 10.0.9.43 inet6 2001:4830:1252::2 prefixlen 64 -=[~]=- -=[Thu Feb 05]=- -=[01:32:34]=- [root@cocytus]# ping 10.0.9.42 PING 10.0.9.42 (10.0.9.42): 56 data bytes 64 bytes from 10.0.9.42: icmp_seq=0 ttl=255 time=0.839 ms 64 bytes from 10.0.9.42: icmp_seq=1 ttl=255 time=0.614 ms --- 10.0.9.42 ping statistics --- 2 packets transmitted, 2 packets received, 0.0% packet loss round-trip min/avg/max/std-dev = 0.614/0.726/0.839/0.115 ms -=[~]=- -=[Thu Feb 05]=- -=[01:33:19]=- [root@cocytus]# ping 10.0.9.42 -=[~]=- -=[Thu Feb 05]=- -=[01:33:22]=- [root@cocytus]# ping6 2001:4830:1252::1 PING6(56=40+8+8 bytes) 2001:4830:1252::2 --> 2001:4830:1252::1 ^C --- 2001:4830:1252::1 ping6 statistics --- 4 packets transmitted, 0 packets received, 100.0% packet loss -=[~]=- -=[Thu Feb 05]=- -=[01:33:29]=- [root@cocytus]# ndp -a Neighbor Linklayer Address Netif Expire S Flags 2001:4830:1252::1 (incomplete) vr3 expired I 3 2001:4830:1252::2 0:0:24:c8:e1:7 vr3 permanent R ... -=[~]=- -=[Thu Feb 05]=- -=[01:33:32]=- [root@cocytus]# I've also tried all this using eui64, again, not working. The host side is OpenBSD cisco is: Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE, RELEASE SOFTWARE (fc1)