A dummy error - low MTU vs ipv6

After configuring IPv6 under an interface, see the ipv6 neighbor or host resolution doesn't work.

Router1.10:36:22(config-if-Po5)#sh ipv6 interface po5
Port-Channel5 is up, line protocol is up (connected)
  IPv6 is stalled, link-local is unassigned
  Global unicast address(es):
    2000:170:1:170::1, subnet is 2000:170:1:170::/64 [INACTIVE]
  No joined group addresses
  ND DAD status is unavailable
  ND Reachable time is 30000 milliseconds
  ND retransmit interval is 1000 milliseconds

The reason is that, I have a line of a left-over configuration of smaller-than-normal mtu size - 1200. The lowest MTU size of IPv6 is 1280.

interface Port-Channel5
   description Cdn_Test_upLink
   mtu 1200
   no switchport
   vrf IxCdn
   ip address 170.1.170.1/24
   ipv6 nd cache expire 60
   ipv6 enable
   ipv6 address 2000:170:1:170::1/64
   ipv6 nd ra disabled all
   no mpls ip
   no qos trust
   spanning-tree bpdufilter enable

After removing this line, everything is fine.

Port-Channel5 is up, line protocol is up (connected)
  IPv6 is enabled, link-local is fe80::464c:a8ff:fea5:1140/64
  Global unicast address(es):
    2000:170:1:170::1, subnet is 2000:170:1:170::/64
  Joined group address(es):
    ff02::1
    ff02::1:ff00:1
    ff02::1:ffa5:1140