This section consists of setup examples with firewall-based load balancing methods.
Example 1
Failover With Firewall Marking
This example demonstrates how to set up failover with a firewall mangle, filter and NAT rules.
Detailed Section Overview
IP address
In this example, our provider assigned two upstream links, one connected to ether1 and other to ether2. Our local network has two subnets 192.168.1.0/24 and 192.168.2.0/24
/ip address add address=10.1.101.18/30 interface=ether1 add address=10.1.200.18/30 interface=ether2 add address=192.168.1.1/24 interface=ether3 add address=192.168.2.1/24 interface=ether4
Mangle
Connections going through the ether1 interface is marked as "first" and packets going through the ether2 is marked as "other":
/ip firewall mangle add action=mark-connection chain=forward connection-mark=no-mark new-connection-mark=first out-interface=ether1 passthrough=yes add action=mark-connection chain=forward connection-mark=no-mark new-connection-mark=other out-interface=ether2 passthrough=yes
Firewall Filter
When the primary link will fail, we will reject all the established connections, so new connections will pass through the secondary link. The same behavior will happen when a primary link will come back again and here we will prevent local IP leakage to a public network, which is one of masquerades disadvantages:
/ip firewall filter add action=reject chain=forward connection-mark=other out-interface=ether1 reject-with=icmp-network-unreachable add action=reject chain=forward connection-mark=first out-interface=ether2 reject-with=icmp-network-unreachable
NAT
Instead of masquerade, we will use src-nat for our local networks, because we do not want to purge connections which are one of the masquerade's main features when a primary link fails. We will restrict them with firewall rules (later in this example):
/ip firewall nat add action=src-nat chain=srcnat out-interface=ether1 to-address=10.1.101.18 add action=src-nat chain=srcnat out-interface=ether2 to-address=10.1.200.18
Routes
We will add two default routes. With distance parameter we set route preference:
/ip route add gateway=10.1.101.17 distance=1 check-gateway=ping /ip route add gateway=10.1.200.17 distance=2
Example 2
Load Balancing Multiple Same Subnet Links
This example demonstrates how to set up load balancing if the provider is giving IP addresses from the same subnet for all links.
Detailed Section Overview
IP address
In this example, our provider assigned two upstream links, one connected to ether1 and the other to ether2. Both links have IP addresses from the same subnet. Our local network has two subnets 192.168.1.0/24 and 192.168.2.0/2:
/ip address add address=10.1.101.18/24 interface=ether1 add address=10.1.101.10/24 interface=ether2 add address=192.168.1.1/24 interface=ether3 add address=192.168.2.1/24 interface=ether4
After the IP address is set up, the connected route will be installed as an ECMP route:
[admin@MikroTik] > /ip route print detail
0 ADC dst-address=10.1.101.0/24 pref-src=10.1.101.18 gateway=ether1,ether2
gateway-status=ether1 reachable,ether2 reachable distance=0 scope=10
Mangle
In our example, very simple policy routing is used. Let`s start with adding routing tables for each mangle mark:
/routing table add fib name=first add fib name=other
Clients from the 192.168.1.0/24 subnet are marked to use the "first" routing table and 192.168.2.0/24 to use the "other" subnet:
/ip firewall mangle add action=mark-routing chain=prerouting src-address=192.168.1.0/24 new-routing-mark=first add action=mark-routing chain=prerouting src-address=192.168.2.0/24 new-routing-mark=other
NAT
And masquerade our local network:
/ip firewall nat add action=masquerade chain=srcnat out-interface=ether1 add action=masquerade chain=srcnat out-interface=ether2
The same can be achieved by setting up route rules instead of mangle.
Routes
We are adding two gateways, one to resolve in the "first" routing table and another to the "other" routing table:
/ip route add gateway=10.1.101.1@main routing-table=first add gateway=10.1.101.1@main routing-table=other
Example 3 (PCC)
Load Balancing With Per Connection Classifier
Overview
PCC matcher will allow you to divide traffic into equal streams with the ability to keep packets with a specific set of options in one particular stream (you can specify this set of options from src-address, src-port, dst-address, dst-port, etc.) PCC takes selected fields from the IP header, and with the help of a hashing algorithm converts selected fields into 32-bit values. This value then is divided by a specified Denominator and the remainder then is compared to a specified Remainder, if equal the packet will be captured. You can choose from src-address, dst-address, src-port, dst-port from the header to use in this operation.
per-connection-classifier= PerConnectionClassifier ::= [!]ValuesToHash:Denominator/Remainder Remainder ::= 0..4294967295 (integer number) Denominator ::= 1..4294967295 (integer number) ValuesToHash ::= both-addresses|both-ports|dst-address-and-port| src-address|src-port|both-addresses-and-ports|dst-address|dst-port|src-address-and-port
Detailed Section Overview
IP address
The router has two upstream ether1 and ether2 interfaces with the addresses of 10.111.0.2/24 and 10.112.0.2/24. The ether3 interface has an IP address of 192.168.1.1/24.
/ip address add address=192.168.1.1/24 network=192.168.0.0 broadcast=192.168.0.255 interface=ether3 add address=10.111.0.2/30 network=10.111.0.0 broadcast=10.111.0.255 interface=ether1 add address=10.112.0.2/30 network=10.112.0.0 broadcast=10.112.0.255 interface=ether2
Mangle
With policy routing, it is possible to force all traffic to the specific gateway, even if traffic is destined to the host (other than gateway) from the connected networks. This way routing loop will be generated and communications with those hosts will be impossible. To avoid this situation we need to allow usage of the default routing table for traffic to connected networks:
/ip firewall mangle add chain=prerouting dst-address=10.111.0.0/30 action=accept in-interface=ether3 add chain=prerouting dst-address=10.112.0.0/30 action=accept in-interface=ether3
First, it is necessary to manage connections initiated from outside - replies must leave via the same interface (from the same Public IP) request came. We will mark all new incoming connections, to remember what was the interface.
/ip firewall mangle add chain=prerouting in-interface=ether1 connection-mark=no-mark action=mark-connection new-connection-mark=ISP1_conn add chain=prerouting in-interface=ether2 connection-mark=no-mark action=mark-connection new-connection-mark=ISP2_conn
Before configuring mark-routing, we have to create a routing table for each of them:
/routing/table add fib name=to_ISP1 add fib name=to_ISP2
Action mark-routing can be used only in mangle chain output and prerouting, but mangle chain prerouting is capturing all traffic that is going to the router itself. To avoid this we will use dst-address-type=!local. And with the help of the new PCC, we will divide traffic into two groups based on source and destination addresses:
/ip firewall mangle add chain=prerouting in-interface=ether3 connection-mark=no-mark dst-address-type=!local per-connection-classifier=both-addresses:2/0 action=mark-connection new-connection-mark=ISP1_conn add chain=prerouting in-interface=ether3 connection-mark=no-mark dst-address-type=!local per-connection-classifier=both-addresses:2/1 action=mark-connection new-connection-mark=ISP2_conn
Then we need to mark all packets from those connections with a proper mark. As policy routing is required only for traffic going to the Internet, do not forget to specify the in-interface option:
/ip firewall mangle add chain=prerouting connection-mark=ISP1_conn in-interface=ether3 action=mark-routing new-routing-mark=to_ISP1 add chain=prerouting connection-mark=ISP2_conn in-interface=ether3 action=mark-routing new-routing-mark=to_ISP2 add chain=output connection-mark=ISP1_conn action=mark-routing new-routing-mark=to_ISP1 add chain=output connection-mark=ISP2_conn action=mark-routing new-routing-mark=to_ISP2
NAT
As routing decision is already made we just need rules that will fix src-addresses for all outgoing packets. If this packet will leave via wlan1 it will be NATed to 10.112.0.2, if via wlan2 then NATed to 10.111.0.2:
/ip firewall nat add chain=srcnat out-interface=ether1 action=masquerade add chain=srcnat out-interface=ether2 action=masquerade
Routes
Create a route for each routing-mark
/ip route add gateway=10.111.0.1@main routing-table=to_ISP1 check-gateway=ping add gateway=10.112.0.1@main routing-table=to_ISP2 check-gateway=ping
Example 4: (NTH)
Load Balancing With NTH
Overview
Every rule has its own counter. When the rule receives a packet counter for a current rule is increased by one. If the counter matches the value of 'every' packet will be matched and the counter will be set to zero.
To match 50% of all traffic only with one rule:
/ip firewall mangle add action=mark-packet chain=prerouting new-packet-mark=AAA nth=2,1;
To split traffic into more than two parts we can use the following configuration. The first rule sees all packets and matches 1/3 of all, the second rule sees 2/3 of packets and matches half of them, the third rule sees and matches all packets that passed through the first two rules ( 1/3 of all packets ):
/ip firewall mangle add action=mark-packet chain=prerouting new-packet-mark=AAA nth=3,1 passthrough=no; add action=mark-packet chain=prerouting new-packet-mark=BBB nth=2,1 passthrough=no; add action=mark-packet chain=prerouting new-packet-mark=CCC ;
This example is a different version of the round-robin load balancing example. It adds persistent user sessions, i.e. a particular user would use the same source IP address for all outgoing connections. Consider the following network layout:
Detailed Section Overview
IP Addresses
The router has two upstream (WAN) interfaces with the addresses 10.111.0.2/24 and 10.112.0.2/24. The LAN interface has the name "Local" and an IP address of 192.168.1.1/24.
/ ip address add address=192.168.1.1/24 network=192.168.1.0 broadcast=192.168.1.255 interface=Local add address=10.111.0.2/24 network=10.111.0.0 broadcast=10.111.0.255 interface=ether2 add address=10.112.0.2/24 network=10.112.0.0 broadcast=10.112.0.255 interface=ether1
Mangle
All traffic from customers having their IP address previously placed in the address list "odd" is instantly marked with connection and routing marks "odd". Afterward, the traffic is excluded from processing against successive mangle rules in the prerouting chain:
/ ip firewall mangle add chain=prerouting src-address-list=odd in-interface=Local action=mark-connection new-connection-mark=odd passthrough=yes add chain=prerouting src-address-list=odd in-interface=Local action=mark-routing new-routing-mark=odd
The same configuration as above, only for customers having their IP address previously placed in the address list "even":
/ ip firewall mangle add chain=prerouting src-address-list=even in-interface=Local action=mark-connection new-connection-mark=even passthrough=yes add chain=prerouting src-address-list=even in-interface=Local action=mark-routing new-routing-mark=even
First, we take every second packet that establishes a new session (note connection-state=new), and mark it with the connection mark "odd". Consequently, all successive packets belonging to the same session will carry the connection mark "odd". Note that we are passing these packets to the second and third rules (passthrough=yes). The second rule adds the IP address of the client to the address list to enable all successive sessions to go through the same gateway. The third rule places the routing mark "odd" on all packets that belong to the "odd" connection and stops processing all other mangle rules for these packets in the prerouting chain:
/ ip firewall mangle add chain=prerouting in-interface=Local connection-state=new nth=2,1 action=mark-connection new-connection-mark=odd passthrough=yes add chain=prerouting in-interface=Local action=add-src-to-address-list address-list=odd address-list-timeout=1d connection-mark=odd passthrough=yes add chain=prerouting in-interface=Local connection-mark=odd action=mark-routing new-routing-mark=odd passthrough=no
These rules do the same for the remaining half of the traffic as the first three rules for the first half of the traffic.
The following code effectively means that each new connection initiated through the router from the local network will be marked as either "odd" or "even" with both routing and connection marks.
/ ip firewall mangle add chain=prerouting in-interface=Local connection-state=new nth=2,2 action=mark-connection new-connection-mark=even passthrough=yes add chain=prerouting in-interface=Local action=add-src-to-address-list address-list=even address-list-timeout=1d connection-mark=even passthrough=yes add chain=prerouting in-interface=Local connection-mark=even action=mark-routing new-routing-mark=even passthrough=no
The above works fine. There are however some situations where you might find that the same IP address is listed under both the ODD and EVEN scr-address-lists. This behavior causes issues with apps that require persistent connections. A simple remedy for this situation is to add the following statement to your mangle rules and this will ensure that the new connection will not already be part of the ODD src-address-list. You will have to do the same for the ODD mangle rule thus excluding IPs already part of the EVEN scr-address-list:
add chain=prerouting in-interface=Local connection-state=new nth=2,2 src-address-list=!odd action=mark-connection new-connection-mark=even passthrough=yes
NAT
Fix the source address according to the outgoing interface:
/ ip firewall nat add chain=srcnat out-interface=ether1 action=masquerade add chain=srcnat out-interface=ether2 action=masquerade
Routes
For all traffic marked "odd" (consequently having 10.111.0.2 translated source address) we use 10.111.0.1 gateway. In the same manner, all traffic marked "even" is routed through the 10.112.0.1 gateway.
/ ip route add dst-address=0.0.0.0/0 gateway=10.111.0.1 scope=255 target-scope=10 routing-mark=odd add dst-address=0.0.0.0/0 gateway=10.112.0.1 scope=255 target-scope=10 routing-mark=even
Finally, we have one additional entry specifying that traffic from the router itself (the traffic without any routing marks) should go to the 10.111.0.2 gateway:
add dst-address=0.0.0.0/0 gateway=10.111.0.2 scope=255 target-scope=10