IPv6 is stalled

vid ett par tillfällen har jag varit med om att IPv6 har stannat på ett interface på Cisco-utrustning. T.ex. kan det se ut så här på ett vlan-interface:

Switch#sh ipv6 int vlan 3 
Vlan3 is up, line protocol is up 
  IPv6 is stalled, link-local address is FE80::EE30:91FF:FE4B:5842 [DUP] 
  No Virtual link-local address(es): 
  Global unicast address(es): 
    2001:aaaa:bbbb:1206::1, subnet is 2001:aaaa:bbbb:1206::/64 [TEN] 
  Joined group address(es): 
    FF02::1 
  MTU is 1500 bytes 
  ICMP error messages limited to one every 100 milliseconds 
  ICMP redirects are enabled 
  ICMP unreachables are sent 
  Output features: Check hwidb 
  ND DAD is enabled, number of DAD attempts: 1 
  ND reachable time is 30000 milliseconds (using 22646) 
  Default router is FE80::EE30:91FF:FE4B:1BC1 on Vlan2

Switchen tyckte att det var duplicate på link-local adressen.

Jag löste det så här genom at först sätta en fast link-local address och sedan ta bort den igen:

Switch(config)#int vlan 3 
Switch(config-if)#ipv6 address fe80::1111 link-local 
Switch(config-if)#^Z 
Switch# 
Switch#sh ipv6 int vlan 3 
Vlan3 is up, line protocol is up 
  IPv6 is enabled, link-local address is FE80::1111 
  No Virtual link-local address(es): 
  Global unicast address(es): 
    2001:aaaa:bbbb:1206::1, subnet is 2001:aaaa:bbbb:1206::/64 
  Joined group address(es): 
    FF02::1 
    FF02::2 
    FF02::1:FF00:1 
    FF02::1:FF00:1111 
  MTU is 1500 bytes 
  ICMP error messages limited to one every 100 milliseconds 
  ICMP redirects are enabled 
  ICMP unreachables are sent 
  Output features: Check hwidb 
  ND DAD is enabled, number of DAD attempts: 1 
  ND reachable time is 30000 milliseconds (using 33127) 
  ND advertised reachable time is 0 (unspecified) 
  ND advertised retransmit interval is 0 (unspecified) 
  ND router advertisements are sent every 200 seconds 
  ND router advertisements live for 1800 seconds 
  ND advertised default router preference is Medium 
  Hosts use stateless autoconfig for addresses. 
Switch#sh run int vlan 3 
Building configuration... 

Current configuration : 133 bytes 
! 
interface Vlan3 
 ip address 10.4.6.1 255.255.255.0 
 ipv6 address FE80::1111 link-local 
 ipv6 address 2001:aaaa:bbbb:1206::1/64 
end 

Switch#conf t 
Enter configuration commands, one per line. End with CNTL/Z. 
Switch(config)#int vlan 3 
Switch(config-if)#no ipv6 address fe80::1111 link-local 
Switch(config-if)#^Z

Efter det såg det bättre ut.

Switch#sh run int vlan 3 
Vlan3 is up, line protocol is up 
  IPv6 is enabled, link-local address is FE80::EE30:91FF:FE4B:5842 
  No Virtual link-local address(es): 
  Global unicast address(es): 
    2001:aaaa:bbbb:1206::1, subnet is 2001:aaaa:bbbb:1206::/64 
  Joined group address(es): 
    FF02::1 
    FF02::2 
    FF02::1:FF00:1 
    FF02::1:FF4B:5842 
  MTU is 1500 bytes 
  ICMP error messages limited to one every 100 milliseconds 
  ICMP redirects are enabled 
  ICMP unreachables are sent 
  Output features: Check hwidb 
  ND DAD is enabled, number of DAD attempts: 1 
  ND reachable time is 30000 milliseconds (using 33127) 
  ND advertised reachable time is 0 (unspecified) 
  ND advertised retransmit interval is 0 (unspecified) 
  ND router advertisements are sent every 200 seconds 
  ND router advertisements live for 1800 seconds 
  ND advertised default router preference is Medium 
  Hosts use stateless autoconfig for addresses. 
Switch#

Varför det blev ett sådant här fel kan jag inte säga med bestämdhet, men jag misstänker att någon har råkat koppla ihop två portar på switchen så att den ser sig själv.