Hey thanks for you comments!
I just updated to v7.12 and both units stay as Root Bridge, but the connection does not break anymore when changing priorities on either unit. So a small step forward.
I also reset both units to factory default and started from there. Same issue. So here the two configs... Firewall-stuff is default on both units but disabled on second one. Basically just created the vlans and did the switch setup and adjusted basic IP-stuff.
Unit 1:
# 1970-01-02 01:34:12 by RouterOS 7.12
# software id =
#
# model = RBD52G-5HacD2HnD
# serial number =
/interface bridge
add admin-mac=XX:XX:XX:XX:XX:01 auto-mac=no comment=defconf name=bridge
/interface wireless
set [ find default-name=wlan1 ] distance=indoors frequency=auto installation=\
indoor mode=ap-bridge ssid=MikroTik wireless-protocol=802.11
set [ find default-name=wlan2 ] distance=indoors frequency=auto installation=\
indoor mode=ap-bridge ssid=MikroTik wireless-protocol=802.11
/interface vlan
add interface=bridge name=vlan11 vlan-id=11
add interface=bridge name=vlan12 vlan-id=12
/interface ethernet switch port
set 1 vlan-header=add-if-missing vlan-mode=secure
set 2 default-vlan-id=11 vlan-header=always-strip vlan-mode=secure
set 3 default-vlan-id=11 vlan-header=always-strip vlan-mode=secure
set 4 default-vlan-id=11 vlan-header=always-strip vlan-mode=secure
set 5 vlan-mode=secure
/interface list
add comment=defconf name=WAN
add comment=defconf name=LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/ip hotspot profile
set [ find default=yes ] html-directory=hotspot
/ip pool
add name=default-dhcp ranges=192.168.11.201-192.168.11.250
/ip dhcp-server
add address-pool=default-dhcp interface=vlan11 lease-time=10m name=defconf
/interface bridge port
add bridge=bridge comment=defconf interface=ether2
add bridge=bridge comment=defconf interface=ether3
add bridge=bridge comment=defconf interface=ether4
add bridge=bridge comment=defconf interface=ether5
add bridge=bridge comment=defconf disabled=yes interface=wlan1
add bridge=bridge comment=defconf disabled=yes interface=wlan2
/ip neighbor discovery-settings
set discover-interface-list=LAN
/interface ethernet switch vlan
add independent-learning=yes ports=ether2,ether3,ether4,ether5,switch1-cpu \
switch=switch1 vlan-id=11
add independent-learning=yes ports=ether2,switch1-cpu switch=switch1 vlan-id=\
12
/interface list member
add comment=defconf disabled=yes interface=bridge list=LAN
add comment=defconf interface=ether1 list=WAN
add interface=vlan11 list=LAN
/ip address
add address=192.168.11.1/24 comment=defconf interface=vlan11 network=\
192.168.11.0
/ip dhcp-client
add comment=defconf interface=ether1
/ip dhcp-server network
add address=192.168.11.0/24 comment=defconf dns-server=192.168.11.1 gateway=\
192.168.11.1
/ip dns
set allow-remote-requests=yes
/ip dns static
add address=192.168.88.1 comment=defconf disabled=yes name=router.lan
/ip firewall filter
add action=accept chain=input comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked
add action=drop chain=input comment="defconf: drop invalid" connection-state=\
invalid
add action=accept chain=input comment="defconf: accept ICMP" protocol=icmp
add action=accept chain=input comment=\
"defconf: accept to local loopback (for CAPsMAN)" dst-address=127.0.0.1
add action=drop chain=input comment="defconf: drop all not coming from LAN" \
in-interface-list=!LAN
add action=accept chain=forward comment="defconf: accept in ipsec policy" \
ipsec-policy=in,ipsec
add action=accept chain=forward comment="defconf: accept out ipsec policy" \
ipsec-policy=out,ipsec
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" \
connection-state=established,related hw-offload=yes
add action=accept chain=forward comment=\
"defconf: accept established,related, untracked" connection-state=\
established,related,untracked
add action=drop chain=forward comment="defconf: drop invalid" \
connection-state=invalid
add action=drop chain=forward comment=\
"defconf: drop all from WAN not DSTNATed" connection-nat-state=!dstnat \
connection-state=new in-interface-list=WAN
/ip firewall nat
add action=masquerade chain=srcnat comment="defconf: masquerade" \
ipsec-policy=out,none out-interface-list=WAN
/ipv6 firewall address-list
add address=::/128 comment="defconf: unspecified address" list=bad_ipv6
add address=::1/128 comment="defconf: lo" list=bad_ipv6
add address=fec0::/10 comment="defconf: site-local" list=bad_ipv6
add address=::ffff:0.0.0.0/96 comment="defconf: ipv4-mapped" list=bad_ipv6
add address=::/96 comment="defconf: ipv4 compat" list=bad_ipv6
add address=100::/64 comment="defconf: discard only " list=bad_ipv6
add address=2001:db8::/32 comment="defconf: documentation" list=bad_ipv6
add address=2001:10::/28 comment="defconf: ORCHID" list=bad_ipv6
add address=3ffe::/16 comment="defconf: 6bone" list=bad_ipv6
/ipv6 firewall filter
add action=accept chain=input comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked
add action=drop chain=input comment="defconf: drop invalid" connection-state=\
invalid
add action=accept chain=input comment="defconf: accept ICMPv6" protocol=\
icmpv6
add action=accept chain=input comment="defconf: accept UDP traceroute" port=\
33434-33534 protocol=udp
add action=accept chain=input comment=\
"defconf: accept DHCPv6-Client prefix delegation." dst-port=546 protocol=\
udp src-address=fe80::/10
add action=accept chain=input comment="defconf: accept IKE" dst-port=500,4500 \
protocol=udp
add action=accept chain=input comment="defconf: accept ipsec AH" protocol=\
ipsec-ah
add action=accept chain=input comment="defconf: accept ipsec ESP" protocol=\
ipsec-esp
add action=accept chain=input comment=\
"defconf: accept all that matches ipsec policy" ipsec-policy=in,ipsec
add action=drop chain=input comment=\
"defconf: drop everything else not coming from LAN" in-interface-list=\
!LAN
add action=accept chain=forward comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked
add action=drop chain=forward comment="defconf: drop invalid" \
connection-state=invalid
add action=drop chain=forward comment=\
"defconf: drop packets with bad src ipv6" src-address-list=bad_ipv6
add action=drop chain=forward comment=\
"defconf: drop packets with bad dst ipv6" dst-address-list=bad_ipv6
add action=drop chain=forward comment="defconf: rfc4890 drop hop-limit=1" \
hop-limit=equal:1 protocol=icmpv6
add action=accept chain=forward comment="defconf: accept ICMPv6" protocol=\
icmpv6
add action=accept chain=forward comment="defconf: accept HIP" protocol=139
add action=accept chain=forward comment="defconf: accept IKE" dst-port=\
500,4500 protocol=udp
add action=accept chain=forward comment="defconf: accept ipsec AH" protocol=\
ipsec-ah
add action=accept chain=forward comment="defconf: accept ipsec ESP" protocol=\
ipsec-esp
add action=accept chain=forward comment=\
"defconf: accept all that matches ipsec policy" ipsec-policy=in,ipsec
add action=drop chain=forward comment=\
"defconf: drop everything else not coming from LAN" in-interface-list=\
!LAN
/system identity
set name=Unit1
/system note
set show-at-login=no
/tool mac-server
set allowed-interface-list=LAN
/tool mac-server mac-winbox
set allowed-interface-list=LAN
Unit 2:
# 1970-01-02 01:07:37 by RouterOS 7.12
# software id =
#
# model = RBD52G-5HacD2HnD
# serial number =
/interface bridge
add admin-mac=XX:XX:XX:XX:XX:02 auto-mac=no comment=defconf name=bridge
/interface wireless
set [ find default-name=wlan1 ] distance=indoors frequency=auto installation=\
indoor mode=ap-bridge ssid=MikroTik wireless-protocol=802.11
set [ find default-name=wlan2 ] distance=indoors frequency=auto installation=\
indoor mode=ap-bridge ssid=MikroTik wireless-protocol=802.11
/interface vlan
add interface=bridge name=vlan11 vlan-id=11
add interface=bridge name=vlan12 vlan-id=12
/interface ethernet switch port
set 0 vlan-header=add-if-missing vlan-mode=secure
set 1 default-vlan-id=11 vlan-header=always-strip vlan-mode=secure
set 2 default-vlan-id=11 vlan-header=always-strip vlan-mode=secure
set 3 default-vlan-id=12 vlan-header=always-strip vlan-mode=secure
set 4 default-vlan-id=12 vlan-header=always-strip vlan-mode=secure
set 5 vlan-mode=secure
/interface list
add comment=defconf name=WAN
add comment=defconf name=LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/ip hotspot profile
set [ find default=yes ] html-directory=hotspot
/interface bridge port
add bridge=bridge comment=defconf interface=ether2
add bridge=bridge comment=defconf interface=ether3
add bridge=bridge comment=defconf interface=ether4
add bridge=bridge comment=defconf interface=ether5
add bridge=bridge comment=defconf disabled=yes interface=wlan1
add bridge=bridge comment=defconf disabled=yes interface=wlan2
add bridge=bridge comment="no WAN" interface=ether1
/ip neighbor discovery-settings
set discover-interface-list=LAN
/interface ethernet switch vlan
add independent-learning=yes ports=ether1,ether2,ether3,switch1-cpu switch=\
switch1 vlan-id=11
add independent-learning=yes ports=ether1,ether4,ether5,switch1-cpu switch=\
switch1 vlan-id=12
/interface list member
add comment=defconf disabled=yes interface=bridge list=LAN
add interface=vlan11 list=LAN
/ip address
add address=192.168.11.2/24 comment=defconf interface=vlan11 network=\
192.168.11.0
/ip dns
set allow-remote-requests=yes
/ip dns static
add address=192.168.88.1 comment=defconf disabled=yes name=router.lan
/ip firewall filter
add action=accept chain=input comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked disabled=yes
add action=drop chain=input comment="defconf: drop invalid" connection-state=\
invalid disabled=yes
add action=accept chain=input comment="defconf: accept ICMP" disabled=yes \
protocol=icmp
add action=accept chain=input comment=\
"defconf: accept to local loopback (for CAPsMAN)" disabled=yes \
dst-address=127.0.0.1
add action=drop chain=input comment="defconf: drop all not coming from LAN" \
disabled=yes in-interface-list=!LAN
add action=accept chain=forward comment="defconf: accept in ipsec policy" \
disabled=yes ipsec-policy=in,ipsec
add action=accept chain=forward comment="defconf: accept out ipsec policy" \
disabled=yes ipsec-policy=out,ipsec
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" \
connection-state=established,related disabled=yes hw-offload=yes
add action=accept chain=forward comment=\
"defconf: accept established,related, untracked" connection-state=\
established,related,untracked disabled=yes
add action=drop chain=forward comment="defconf: drop invalid" \
connection-state=invalid disabled=yes
add action=drop chain=forward comment=\
"defconf: drop all from WAN not DSTNATed" connection-nat-state=!dstnat \
connection-state=new disabled=yes in-interface-list=WAN
/ip firewall nat
add action=masquerade chain=srcnat comment="defconf: masquerade" disabled=yes \
ipsec-policy=out,none out-interface-list=WAN
/ipv6 firewall address-list
add address=::/128 comment="defconf: unspecified address" list=bad_ipv6
add address=::1/128 comment="defconf: lo" list=bad_ipv6
add address=fec0::/10 comment="defconf: site-local" list=bad_ipv6
add address=::ffff:0.0.0.0/96 comment="defconf: ipv4-mapped" list=bad_ipv6
add address=::/96 comment="defconf: ipv4 compat" list=bad_ipv6
add address=100::/64 comment="defconf: discard only " list=bad_ipv6
add address=2001:db8::/32 comment="defconf: documentation" list=bad_ipv6
add address=2001:10::/28 comment="defconf: ORCHID" list=bad_ipv6
add address=3ffe::/16 comment="defconf: 6bone" list=bad_ipv6
/ipv6 firewall filter
add action=accept chain=input comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked disabled=yes
add action=drop chain=input comment="defconf: drop invalid" connection-state=\
invalid disabled=yes
add action=accept chain=input comment="defconf: accept ICMPv6" disabled=yes \
protocol=icmpv6
add action=accept chain=input comment="defconf: accept UDP traceroute" \
disabled=yes port=33434-33534 protocol=udp
add action=accept chain=input comment=\
"defconf: accept DHCPv6-Client prefix delegation." disabled=yes dst-port=\
546 protocol=udp src-address=fe80::/10
add action=accept chain=input comment="defconf: accept IKE" disabled=yes \
dst-port=500,4500 protocol=udp
add action=accept chain=input comment="defconf: accept ipsec AH" disabled=yes \
protocol=ipsec-ah
add action=accept chain=input comment="defconf: accept ipsec ESP" disabled=\
yes protocol=ipsec-esp
add action=accept chain=input comment=\
"defconf: accept all that matches ipsec policy" disabled=yes \
ipsec-policy=in,ipsec
add action=drop chain=input comment=\
"defconf: drop everything else not coming from LAN" disabled=yes \
in-interface-list=!LAN
add action=accept chain=forward comment=\
"defconf: accept established,related,untracked" connection-state=\
established,related,untracked disabled=yes
add action=drop chain=forward comment="defconf: drop invalid" \
connection-state=invalid disabled=yes
add action=drop chain=forward comment=\
"defconf: drop packets with bad src ipv6" disabled=yes src-address-list=\
bad_ipv6
add action=drop chain=forward comment=\
"defconf: drop packets with bad dst ipv6" disabled=yes dst-address-list=\
bad_ipv6
add action=drop chain=forward comment="defconf: rfc4890 drop hop-limit=1" \
disabled=yes hop-limit=equal:1 protocol=icmpv6
add action=accept chain=forward comment="defconf: accept ICMPv6" disabled=yes \
protocol=icmpv6
add action=accept chain=forward comment="defconf: accept HIP" disabled=yes \
protocol=139
add action=accept chain=forward comment="defconf: accept IKE" disabled=yes \
dst-port=500,4500 protocol=udp
add action=accept chain=forward comment="defconf: accept ipsec AH" disabled=\
yes protocol=ipsec-ah
add action=accept chain=forward comment="defconf: accept ipsec ESP" disabled=\
yes protocol=ipsec-esp
add action=accept chain=forward comment=\
"defconf: accept all that matches ipsec policy" disabled=yes \
ipsec-policy=in,ipsec
add action=drop chain=forward comment=\
"defconf: drop everything else not coming from LAN" disabled=yes \
in-interface-list=!LAN
/system identity
set name=Unit2
/system note
set show-at-login=no
/tool mac-server
set allowed-interface-list=LAN
/tool mac-server mac-winbox
set allowed-interface-list=LAN
Spaces are just to have both configs side by side easier.
Kind regards!