Load Balancing Route

###Set Passthrough=no to reduce CPU usage for rules that do not need to be re-validated once they've been processed###
###connection-mark=no-mark to prevent re-marking of already marked connections and hence waste CPU cycles###
/ip firewall mangle
###Incoming connections through ISP1 must leave through ISP1###
add action=mark-connection chain=prerouting connection-mark=no-mark in-interface=pppoe-out1 new-connection-mark=ISP1_conn passthrough=no
###Incoming connections through ISP2 must leave through ISP2###
add action=mark-connection chain=prerouting connection-mark=no-mark in-interface=pppoe-out2 new-connection-mark=ISP2_conn passthrough=no
###I am assuming a 50/50 split ratio between the two ISPs#
###We are using dst-address-list=!not_in_internet && dst-address-type=!local to prevent marking LAN-to-LAN traffic###
###We can use PCC to handle HTTP/HTTPS traffic with "both-addresses" attribute to reduce chances of connections being marked more "randomly" which would break the connections as then connections would go through ISP1 and ISP2 more "randomly" and break. However in this case, I used "both-addresses-and-ports" based on my personal experience of traffic working just fine###
###For old school HTTP/HTTPS traffic###
###50% going to ISP1###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local dst-port=80,443 in-interface-list=LAN new-connection-mark=ISP1_conn passthrough=yes per-connection-classifier=both-addresses-and-ports:2/0 protocol=tcp
###50% going to ISP2###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local dst-port=80,443 in-interface-list=LAN new-connection-mark=ISP2_conn passthrough=yes per-connection-classifier=both-addresses-and-ports:2/1 protocol=tcp
###For new school HTTP3 traffic aka QUIC###
###50% going to ISP1###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local dst-port=80,443 in-interface-list=LAN new-connection-mark=ISP1_conn passthrough=yes per-connection-classifier=both-addresses-and-ports:2/0 protocol=udp
###50% going to ISP2###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local dst-port=80,443 in-interface-list=LAN new-connection-mark=ISP2_conn passthrough=yes per-connection-classifier=both-addresses-and-ports:2/1 protocol=udp
###If you have a third uplink, then the split ratio would be 3/0, 3/1, 3/2###
###Now we will use Nth for non HTTP/HTTPs traffic in order to acheieve bandwidth aggregation###
###50% going to ISP1###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local in-interface-list=LAN new-connection-mark=ISP1_conn nth=2,1 passthrough=yes
###50% going to ISP2###
add action=mark-connection chain=prerouting connection-mark=no-mark dst-address-list=!not_in_internet dst-address-type=!local in-interface-list=LAN new-connection-mark=ISP2_conn nth=2,2 passthrough=yes
###Now we will send the marked connections to their appropriate routing table###
###For our marked/split traffic###
add action=mark-routing chain=prerouting connection-mark=ISP1_conn in-interface-list=LAN new-routing-mark=to_ISP1 passthrough=no
add action=mark-routing chain=prerouting connection-mark=ISP2_conn in-interface-list=LAN new-routing-mark=to_ISP2 passthrough=no
###For the incoming traffic from WAN###
add action=mark-routing chain=output connection-mark=ISP1_conn new-routing-mark=to_ISP1 out-interface=pppoe-out1 passthrough=no
add action=mark-routing chain=output connection-mark=ISP2_conn new-routing-mark=to_ISP2 out-interface=pppoe-out2 passthrough=no
###Now Finally we add the required routing tables###
/ip route
add check-gateway=ping comment="Load Balancing Route to ISP 1" distance=1 gateway=pppoe-out1 routing-mark=to_ISP1
add check-gateway=ping comment="Load Balancing Route to ISP 2" distance=1 gateway=pppoe-out2 routing-mark=to_ISP2