In our network, we have several Cisco 1721 routers located at branch offices connected back to the main office via T-1 circuits. All the 1721s are running the same IOS and configured the same, with static global IPv6 addresses on the LAN interface. Here are the relevant configuration items:
ipv6 unicast-routing ! interface FastEthernet0 ip address 172.25.22.254 255.255.255.0 no ip proxy-arp speed auto ipv6 address 2001:xxxx:xxxx:22::1/64 ipv6 enable ! interface Serial0 ip address 172.25.7.42 255.255.255.252 no ip proxy-arp ipv6 enable no ipv6 nd suppress-ra priority-group 1 ! ipv6 route ::/0 Serial0
But I have one router where the FastEthernet0 interface is not initializing IPv6 properly. The IPv6 addresses stay at tentative status:
FastEthernet0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::20C:30FF:FE8E:B1F0 [TENTATIVE] Global unicast address(es): 2001:xxxx:xxxx:22::1, subnet is 2001:xxxx:xxxx:22::/64 [TENTATIVE] Joined group address(es): FF02::1 FF02::2 FF02::1:FF8E:B1F0 FF02::1:FF00:1 MTU is 1500 bytes ICMP error messages limited to one every 100 milliseconds ICMP redirects are enabled ND DAD is enabled, number of DAD attempts: 1 ND reachable time is 30000 milliseconds ND advertised reachable time is 0 milliseconds ND advertised retransmit interval is 0 milliseconds ND router advertisements are sent every 200 seconds ND router advertisements live for 1800 seconds Hosts use stateless autoconfig for addresses.
What could cause this to happen? Where should I start troubleshooting next?
I did try
ipv6 nd dad attempts 0 on that interface with no success.