Load balancing

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The load balancer can dynamically redirect and route traffic. It can operate as

  • Load balancer
  • Application layer gateway
  • SSL accelerator
  • Transparent proxy
  • Internet failover


The load balancer is most commonly used to forward traffic to multiple servers with load distribution and health checking. This functionality can, with some generalization, be divided into layer 3 (called redirects) and layer 4+ (called relays). They are configured in much the same way, but have some striking technical differences. Both the redirects and relays are sometimes referred to as "virtual servers" in other products.

Layer 3 (redirects)

Layer 3 load balancing is implemented as a firewall port forward, which is very efficient, and therefore gives layer 3 load balancing a performance advantage over layer 4+. Because of its implementation, it requires the firewall to be started (simply check if there are any firewall rules in the configuration). Also because if this, it's normally not necessary to add any additional firewall rules. Further, it's necessary that the load balancer is the default route (gateway) of the servers being load balanced, since the source packets of the incoming traffic is maintained. In order words, the topology would look something like:

                          > Server1
Internet > Halon > Switch > Server2
                          > Server3                

To add a layer 3 load balancer, follow these steps

  1. Check that the firewall is enabled by looking for a firewall statement in the configuration, or rules on the Network > Firewall page (if not, add a rule)
  2. Go to the Network > Load balancer page, click the "Pools (tables)" button and then click "Add pool"
  3. Just give it a name, type an IP address in the table's node column (add multiple hosts by pressing the + icon to the right in the table header) and finally click "Apply"
  4. If you like, click the "Node (hosts)" button and give the IP addresses names
  5. Click the "Relays (servers)" button, click "Add..." and select "Redirect (layer 3)"
  6. Just give it a name, listen address (the external virtual IP), listen port, forward pool (the pool you created in step 3) and then click "Apply"
  7. Click the "Cancel" button, then click the newly added relay in the table, and watch the health check status

Configuration examples

Below are a few clear-text configuration examples.

HTTPS (SSL) acceleration

This very simple example provides an HTTPS accelerator. If you are using the 64-bit version (amd64) on a router with AES-NI instructions, you can expect gigabit performance. Below is a more or less complete example, using the router exclusively as a layer 7 load balancer, utilizing only one Ethernet interface.

interface em0 {
	route default
load-balancer {
	table <servers> { }
	relay "webservers" {
		listen on port 443 ssl
		forward to <servers> port 80 check tcp
system {
	http-server {
		port 4433
	authentication {
		root-password "extremelyhardpassword"
		user "admin" {
			password "veryhardpassword"
	dns {

Then, upload the certificate and private key. Currently, these are not in the configuration file. Instead, enable root access (already enabled by the above example) and upload the file using for example sep according to the skeleton files guidelines. You can also try out the load balancer by using the web administration's self-signed certificate, by issuing the following commands when logged in as root:

# cp /etc/ssl/server.crt /etc/ssl/
# cp /etc/ssl/private/server.key /etc/ssl/private/

Internet failover

The load balancer can be used to select one of several default routers (gateways) which is useful for outbound internet failover when more sophisticated protocols such as BGP is unavailable. Below is an incomplete example of such a a configuration.

load-balancer {
	gw1 =
	gw2 =
	table <gateways> { $gw1 ip ttl 1, $gw2 ip ttl 1 }
	router "internetfailover" {
		forward to <gateways> check icmp

SSL stripping

If you would like to strip the SSL from a service that is only available over SSL (eg. the web administration, even thou it's not recommended nor good practice), this example shows how to make the web administration available for unsecure HTTP connections.

load-balancer {
	relay "webui" {
		listen on port 80
		forward with ssl to port 443