Cisco 4221 Router IPv6 Problem

[rbo]

Hi,

Our Cisco 4221 routers we use, won't join the "all routers multicast group" FF02::2 after enabling ipv6 unicast-routing and configuring the interface with ipv6. Sometimes we have to disable "ipv6 unicast-routing" and enabling it again to get it work. As we use them for CCNA training, it is really annoying to help out the students without an explanation. Any advice? Known Issue?

Cisco ISR4221/K9

Cisco IOS XE Software, Version 16.09.02

pin6(config)#ipv6 unicast-routing
pin6(config)#int g0/0/0
pin6(config-if)#ipv6 address 2001:db8:abcd:a::1/64
pin6(config-if)#ipv6 address fe80::1 link-local
pin6(config-if)#no shut

pin6#show ipv6 interface g0/0/0
GigabitEthernet0/0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::1
  No Virtual link-local address(es):
  Global unicast address(es):
    2001:DB8:ABCD:A::1, subnet is 2001:DB8:ABCD:A::/64
  Joined group address(es):
    FF02::1
    FF02::1:FF00:1
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ICMP unreachables are sent
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds (using 30000)
  ND NS retransmit interval is 1000 milliseconds

pin6(config)#no ipv6 unicast-routing
pin6(config)#ipv6 unicast-routing
pin6(config)#exit
pin6#
pin6#
pin6#show ipv6 interface g0/0/0
*Oct 26 10:20:06.661: %SYS-5-CONFIG_I: Configured from console by console
GigabitEthernet0/0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::1
  No Virtual link-local address(es):
  Global unicast address(es):
    2001:DB8:ABCD:A::1, subnet is 2001:DB8:ABCD:A::/64
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::1:FF00:1

[paul driver]

Hello

ipv6 unicast -routing 

int x/x

no ipv6 enable
clear ipv6 nd on-link prefix
clear ipv6 neighbours

[rbo]

Hi Paul,

Sorry for the late response, but this doesn't help at all. I could reconstruct the problem with the Router-Advertisements. You can see that the router sends out RA's every 5 seconds and you can see that some of them doesn't include the "ICMPv6 Option (Source link-layer address: 10:b3:d6:04:d3:c0).

As soon as these Router Advertisement are received by the client, it can't resolve the IP-Address to their correspondent mac-address.

After a while a correct Router Advertisement with the including MAC address of the router interface is received, and pings are going through for 5seconds. (till another bad RA is received)!!!!

I've tested it on a cisco 1941 series router and could see that there are not that many RA's and all of them included the source link-layer address.