When having VLAN without IPv6 address on L3 enabled switch, no RA is passed through VLAN unless there is IPv6 address assigned to the VLAN. Static assigments however are reachable fine.

Switch(config)#interface Vlan 3
  no ipv6 address autoconfig # RA from mikrotik not working
  ipv6 address autoconfig # RA from mikrotik suddenly starts working
  no ipv6 address autoconfig # IPMI immediately losts SLAAC IPv6 address and become unresponsive


-> Uplink -> Cisco (L3 routing to VLANs) -> Servers

I receive non routed /27 IPv4 and /48 IPv6 routed via single /64 on uplink (vlan 1). Cisco therefore does IPv6 routing to VLANs, where each VLAN is assigned unique /64 range with RA enabled. Everyone who needs IPv4 is assigned second port with (mode access + vlan 1).

VLAN 3 is however special as it is delegated through mikrotik (firewall) and the same cisco is then used as L2 switch (access vlan 3). In that case traffic passes cisco twice.

-> Uplink -> Cisco -> (Gi0/2 VLAN 2 -> ether1) Mikrotik (ether2 -> Gi0/3 VLAN 3) -> Cisco -> IPMI

IPMI are then connected to VLAN 3 and delegated IPv6 is expected to be managed via mikrotik.

When we connect IPMI directly to mikrotik, it works without any issue.

show ver

Switch Ports Model              SW Version            SW Image
------ ----- -----              ----------            ----------
*    1 52    WS-C3560G-48TS     15.0(2)SE4            C3560-IPSERVICESK9-M

show running-config

version 15.0
ipv6 unicast-routing
interface GigabitEthernet0/1  # uplink port
interface GigabitEthernet0/2  # ether1 to mikrotik
 switchport access vlan 2
 switchport mode access
interface GigabitEthernet0/3  # ether2 from mikrotik, which manages IPv6 RA
 switchport access vlan 3
 switchport mode access
interface GigabitEthernet0/27 # Example of server uplink
 switchport access vlan 10
 switchport mode access
interface GigabitEthernet0/28 # Example of IPMI uplink
 switchport access vlan 3
 switchport mode access
interface GigabitEthernet0/41 # Example of port with IPv4
 switchport access vlan 1
 switchport mode access
interface Vlan1 # Uplink VLAN
 no ip address
 ipv6 address 2001:db8:0:ffff::1/64
 ipv6 nd ra suppress all
interface Vlan2 # Mikrotik prefix delegation network
 no ip address
 ipv6 address 2001:db8:0:1::1/64
 ipv6 nd ra suppress all
interface Vlan3 # IPMI VLAN - IP addresses are managed by mikrotik
 no ip address
interface Vlan10 # VLAN for servers
 no ip address
 ipv6 address 2001:db8:0:10::1/64
 ipv6 nd managed-config-flag
 ipv6 nd other-config-flag
 ipv6 dhcp relay destination .......
ipv6 route 2001:db8:0:3::/64 2001:db8:0:1::2 # Prefix delegation to mikrotik
ipv6 route ::/0 2001:db8:0:ffff::2

ipv6 address autoconfig

show sdm prefer

The current template is "desktop IPv4 and IPv6 routing" template.
The selected template optimizes the resources in
the switch to support this level of features for
8 routed interfaces and 1024 VLANs.

 number of unicast mac addresses:                  1.5K
 number of IPv4 IGMP groups + multicast routes:    1K
 number of IPv4 unicast routes:                    2.75K
   number of directly-connected IPv4 hosts:        1.5K
   number of indirect IPv4 routes:                 1.25K
 number of IPv6 multicast groups:                  1.125k
 number of directly-connected IPv6 addresses:      1.5K
 number of indirect IPv6 unicast routes:           1.25K
 number of IPv4 policy based routing aces:         0.25K
 number of IPv4/MAC qos aces:                      0.5K
 number of IPv4/MAC security aces:                 0.5K
 number of IPv6 policy based routing aces:         0.25K
 number of IPv6 qos aces:                          0.625k
 number of IPv6 security aces:                     0.5K

1 Answer 1


Fixed by upgrading to IOS 15.0(2)SE10 (c3560-ipservicesk9-mz.150-2.SE4). It's frustrating, I spent whole day on debugging this problem.


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