Keep it simple!! no need for static routes or the like. This is a basic providing private IP to second router using a dedicated LAN subnet.
You can do it many ways, bridge-subnet and ether5 subnet
(or what I usually prefer is VLAN5 for home VLAN10 for guest house).
/ip address
add address=192.168.88.1/24 interface=bridge network=192.168.88.0
add address=10.10.10.1/30 interface=ether5 network=10.10.10.0
/interface bridge ports
add bridge=bridge interface=ether2
add bridge=bridge interface=ether3
add bridge=bridge interface=ether4
/interface list members
add interface=bridge list=LAN
add interface=ether5-guestWAN list=LAN
/ip firewall rules (forward chain)
{ default rules to keep }
add action=fasttrack-connection chain=forward connection-state=established,related
add action=accept chain=forward connection-state=established,related
add action=drop chain=forward connection-state=invalid
{ admin rules }
add action=accept chain=forward comment=“internet traffic” in-interface-list=LAN out-interface-list=WAN
add action=accept chain=forward comment=“port forwarding” connection-nat-state=dstnat disabled=yes { enable or remove if not required }
add action=drop chain=forward comment=“drop all else”
In this way, all users have internet access but ether5 cannot access bridge subnet and bridge subnet cannot access ether5 as there is no layer2 connection between bridge and ether5.
The firewall rules drop all traffic not accepted above drop all rule.
If you were to do it via vlans… all ports are on bridge.
/ip vlan
add interface=bridge name=homeVLAN5 vlan-id=5
add interface=bridge name=guestVLAN10 vlan-id=10
/ip address
add address=192.168.88.1/24 interface=homeVLAN5 network=192.168.88.0
add address=10.10.10.1/30 interface=guestVLAN10 network=10.10.10.0
/interface bridge ports
add bridge=bridge ingress-filtering=yes frame-types=admit-priority-and-untaggged interface=ether2 pvid=5
add bridge=bridge ingress-filtering=yes frame-types=admit-priority-and-untaggged interface=ether3 pvid=5
add bridge=bridge ingress-filtering=yes frame-types=admit-priority-and-untaggged interface=ether4 pvid=5
add bridge=bridge ingress-filtering=yes frame-types=admit-priority-and-untaggged interface=ether5 pvid=10
/interface list members
add interface=homeVLAN5 list=LAN
add interface=guestVLAN10 list=LAN
/ip firewall rules (forward chain)
{ default rules to keep }
add action=fasttrack-connection chain=forward connection-state=established,related
add action=accept chain=forward connection-state=established,related
add action=drop chain=forward connection-state=invalid
{ admin rules }
add action=accept chain=forward comment=“internet traffic” in-interface-list=LAN out-interface-list=WAN
add action=accept chain=forward comment=“port forwarding” connection-nat-state=dstnat disabled=yes { enable or remove if not required }
add action=drop chain=forward comment=“drop all else”
Here vlans keep the two subnets separated at layer2 and firewall rules drop all traffic not accepted above the drop rule.
(note last step is to turn bridge vlan filtering on)
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All the neighbour has to do is plug in his router to your etherport 5 and he gets internet only and an IP address of 10.10.10.2.
The only thing that may require work is if he wants to host some service and that depends if you have a publicly available IP address ( VPN etc…).