Allied Telesis Routers and Switches User manual

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How To|
Introduction
In many Server Hosting environments, two requirements are important: maximising
throughput availability to each service, and minimising service downtime. This How To Note
contributes towards both these aims.
The Note is split into two parts. The first part illustrates both redundancy of servers and
redundancy of the load balancers themselves. The second part provides an optional
extension that enables you to control server selection without losing redundancy. This is
helpful when you prefer to have customers access a certain server, instead of balancing that
traffic. However, if that server fails, the customers need to use the alternate server instead.
The examples
The network configuration for these examples is shown in the following figure.
The Note’s first example illustrates how to load balance web services, and includes:
•Load balancing of incoming web traffic to maximise throughput to web servers. It also
provides redundancy if a web server goes down.
•Redundancy between two load balancing routers. In the unlikely event of a router going
down, a backup router takes over as master and continues the load balancing work for
incoming web connections. Load balancer redundancy and VRRP ensure that clients and
servers access the same public and private addresses no matter which router is the master.
•A firewall to secure the LAN against attack. The firewall configuration changes
automatically if the backup router takes over the load balancing role.
Web/SFTP server 1
192.168.1.1
Web/SFTP server 2
192.168.1.2
private address
192.168.1.201
private
VLAN 3
with VRRP
virtual
address
192.168.1.202
public
VLAN 2
private address
192.168.1.200
public address
172.214.1.3
public address
172.214.1.4
redundancy
management
VLAN 4
192.168.2.2
redundant
load balancer
virtual address
172.214.1.2
Load Balancer 1
Load Balancer 2
client
redundancy
management
VLAN 4
192.168.2.1
public side private side
lb-redundancy.eps
Configure Load Balancer Redundancy on Allied Telesis
Routers and Switches

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 2
The Note’s second example extends the first example by showing how to control server
selection for SFTP (Secure File Transfer Protocol) traffic, while still providing server
redundancy if the preferred server fails.
For simplicity, these examples provide load balancing between two servers. You can easily
expand the examples by adding more servers.
What information will you find in this document?
As outlined above, the Note first describes basic load balancer redundancy. To configure
this, do all the following steps:
•"Configure Load Balancer 1" on page 3
•"Configure Load Balancer 2" on page 7
•"Create the Scripts" on page 9
Then the Note describes the optional extensions that let you control server selection. To
configure this, make all the following additions to the basic configuration:
•"Configure Load Balancing: Extra Commands" on page 10
•"Configure the Triggers: Extra Commands" on page 11
•"Modify the Scripts" on page 11
•"Create New Scripts" on page 12
Finally, the Note gives the complete extended configuration so you can verify your
configuration. Also, you may find it easier to copy this configuration to your router instead of
using the step-by-step configuration.
•"Commands: Load Balancer 1" on page 13
•"Commands: Load Balancer 2" on page 14
•"File: master.scp" on page 15
•"File: slave.scp" on page 15
•"File: sftp1down.scp" on page 15
•"File: sftp1up.scp" on page 15
Which products and software version does it apply to?
We created this configuration using AR440S routers and Software Version 275-05. However,
the configuration applies to the following products:
•AR44xS and AR450S Series routers
•AR750S, AR7x5 routers
•Rapier i Series switches
•AT-8800 Series switches
•AT-9800 Series switches
It requires software version 275-05 or later (except version 276-01, which lacks the
necessary trigger functionality).

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 3
Example of Basic Redundancy
Configure Load Balancer 1
Name this router LB-1.
set system name=LB-1
Create the three VLANs that this example uses:
•VLAN 2 for the public Internet side
create vlan=vlan2 vid=2
•VLAN 3 for the private LAN side
create vlan=vlan3 vid=3
•VLAN 4 for managing the load balancer redundancy
create vlan=vlan4 vid=4
Add ports to the three VLANs.
add vlan=2 port=1
add vlan=3 port=2-4
add vlan=4 port=5
Enable IP.
enable ip
Give the public VLAN a unique public address. Note that public clients will not browse to
this address; they will browse to the virtual balancer’s IP address instead (see step 8).
add ip int=vlan2 ip=172.214.1.3 mask=255.255.255.0
Give the private VLAN a private address. Note that the servers will not use this address as a
gateway; they will use the VRRP virtual address instead (see step 7).
add ip int=vlan3 ip=192.168.1.200
Give the redundancy management VLAN a private address.
add ip int=vlan4 ip=192.168.2.2
1. Name the router
2. Create the VLANs
3. Add ports to the VLANs
4. Configure IP on the VLANs

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 4
Enable the firewall.
enable firewall
Create a firewall policy.
create firewall policy=lb
Set the firewall session timeouts for TCP, UDP and other packet types, in minutes.
set firewall policy=lb tcptimeout=5 udptimeout=5 othertimeout=5
Add the public and private interfaces to the firewall policy.
add firewall policy=lb int=vlan2 type=public
add firewall policy=lb int=vlan3 type=private
Add the redundancy management VLAN to the firewall policy as a private interface.
add firewall policy=lb int=vlan4 type=private
You do not need to add firewall access rules at this step. This example uses triggered scripts
to dynamically add access rules, depending on which load balancer is the master (see step 9).
You cannot use the router’s GUI or its HTTP server on port 80 when load balancing web
traffic. Therefore, you need to either disable the GUI and server, by using the following
commands:
disable gui
disable http server
or change the port that the server uses. For example, to change the port to 8080, use the
following command:
set http server port=8080
You can then use the GUI by pointing your browser to the router's private address and the
new port (in this example, 192.168.1.200:8080).
Note that this configuration uses some advanced settings that are not available through the
GUI, so you cannot use the GUI to create this configuration. You also cannot use the firewall
pages in the GUI to modify this configuration’s firewall settings, because the GUI does not
recognise this firewall policy. However, you can use the GUI to monitor the router.
5. Configure the firewall
6. Disable the GUI and the HTTP server on port 80

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 5
Configure VRRP for the private side interface. This step creates a virtual address for the
private interface of both load balancing routers. Private servers use this address as their
gateway to the Internet, instead of using the address of the private interface of either router.
This means the servers’ gateway is independent of which router is the master load balancer.
enable vrrp
create vrrp=2 over=vlan3 ipaddress=192.168.1.202
When you configure your servers, enter the VRRP address as their gateway address.
Enable load balancing.
enable lb
Add a resource pool for web traffic.
add lb respool=web selectmethod=roundrobin faillast=no
Add resources to the web resource pool. In this example, two resource servers share the
web traffic.
add lb resource=web1 ip=192.168.1.1 port=80 respool=web
add lb resource=web2 ip=192.168.1.2 port=80 respool=web
Add and enable the Virtual Balancer for the web traffic that is to be balanced. This step also
defines the load balancer’s virtual public address. Public clients browse to this address,
instead of browsing to either routers’ public address. This means that the clients’ destination
address is independent of which router is the master load balancer.
add lb virtualbalancer=web publicip=172.214.1.2 publicport=80
respool=web
enable lb virtualbalancer=web
Define the load balancing redundancy peer (Load Balancer 2 in the figure in "The
examples" on page 1).
set lb redundancy peerip=192.168.2.1 listenport=5000
redunip=172.214.1.2 publicint=vlan2 redunmask=255.255.255.0
enable lb redundancy
7. Configure VRRP
8. Configure load balancing

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 6
If one of the load balancers goes down, the firewall configuration needs to change. This
example uses triggers to make this change automatically, by running a script when the state
changes. See "Create the Scripts" on page 9 for instructions for making the scripts.
Enable triggers.
enable trigger
Set the router to run the script master.scp if it becomes the master load balancer. This
script adds firewall allow rules to support the resource pools.
create trigger=2 module=loadbalancer event=master
script=master.scp
Set the router to run the script slave.scp if it becomes the slave load balancer. This script
removes redundant firewall allow rules.
create trigger=3 module=loadbalancer event=slave script=slave.scp
Save the configuration and set the router to use it when it restarts.
create config=lb_redun.cfg
set config=lb_redun.cfg
9. Configure triggers
10. Save the configuration

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 7
Configure Load Balancer 2
Load balancer 2 is identical to load balancer 1, except for its:
•name (which is just a convenience and does not affect how it functions)
•public interface’s IP address
•private interface’s IP address
•load balancer redundancy peer, which is load balancer 1
Because the two load balancers are so similar, the following instructions do not explain the
steps—see the instructions for load balancer 1 for explanations.
set system name=LB-2
create vlan=vlan2 vid=2
create vlan=vlan3 vid=3
create vlan=vlan4 vid=4
add vlan=2 port=1
add vlan=3 port=2-4
add vlan=4 port=5
enable ip
add ip int=vlan2 ip=172.214.1.4 mask=255.255.255.0
add ip int=vlan3 ip=192.168.1.201
add ip int=vlan4 ip=192.168.2.1
enable firewall
create firewall policy=lb
set firewall policy=lb tcptimeout=5 udptimeout=5 othertimeout=5
add firewall policy=lb int=vlan2 type=public
add firewall policy=lb int=vlan3 type=private
add firewall policy=lb int=vlan4 type=private
1. Name the router
2. Create the VLANs
3. Add ports to the VLANs
4. Configure IP on the VLANs
5. Configure the firewall

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 8
Either:
disable gui
disable http server
Or:
set http server port=8080
enable vrrp
create vrrp=2 over=vlan3 ipaddress=192.168.1.202
enable lb
add lb respool=web selectmethod=roundrobin faillast=no
add lb resource=web1 ip=192.168.1.1 port=80 respool=web
add lb resource=web2 ip=192.168.1.2 port=80 respool=web
add lb virtualbalancer=web publicip=172.214.1.2 publicport=80
respool=web
enable lb virtualbalancer=web
set lb redundancy peerip=192.168.2.2 listenport=5000
redunip=172.214.1.2 publicint=vlan2 redunmask=255.255.255.0
enable lb redundancy
enable trigger
create trigger=2 module=loadbalancer event=master
script=master.scp
create trigger=3 module=loadbalancer event=slave script=slave.scp
create config=lb_redun.cfg
set config=lb_redun.cfg
6. Disable the GUI and the HTTP server on port 80
7. Configure VRRP
8. Configure load balancing
9. Configure triggers
10. Save the configuration

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 9
Create the Scripts
This section describes the scripts that the trigger facility runs when the master or slave load
balancer changes. Create the same scripts on both load balancer 1 and load balancer 2.
Create the scripts in a text editor on your PC. You can then open the router’s editor by using
the command edit master.scp (or edit slave.scp) and copy and paste the text of the script
into the editor. Use Ctrl+K+X to save the script and exit.
Alternatively, you can copy your PC-created script to a TFTP server and use the router’s
load command to download the files from the server.
# Add the load balancer virtual interface (vlan2-1) to the firewall policy
# as a public interface.
#
add firewall policy=lb int=vlan2-1 type=public
# Add an allow rule for web traffic access. Note that this rule does not map
# to a private address, as expected on a NAT firewall. It just opens the port.
# The load balancer handles security and NAT redirection to the server.
#
add firewall policy=lb rule=1 int=vlan2-1 action=allow protocol=tcp port=80
# Set the VRRP priority level to a value higher than the slave's priority.
#
set vrrp=2 priority=200
# Remove the load balancer virtual interface (vlan2-1).
#
delete firewall policy=lb int=vlan2-1
# Remove the associated access rule.
#
delete firewall policy=lb rule=1
# Set the VRRP priority level to a value lower than the master's priority.
#
set vrrp=2 priority=100
!Script for when a load balancer becomes the master: master.scp
!Script for when a load balancer becomes the slave: slave.scp

Configure Load Balancer Redundancy on Allied Telesis Routers and Switches 10
Extension: Controlling Server Selection
Sometimes you may prefer your customers to access a certain server for certain traffic types.
However, if that server fails, they still require redundancy to an alternate server.
This section shows how to configure this. The example gives you control over server
selection for SFTP (Secure File Transfer Protocol) traffic, while providing server redundancy if
the preferred server fails. In this example, SFTP favours the first resource only (192.168.1.1).
It only uses the second resource if the first resource fails.
The load balancers use pings to monitor the health of each resource. When the primary
resource fails, this triggers a script to enable the secondary resource.
To provide this solution, you need to add the following steps:
•Configure Load Balancing: Extra Commands
•Configure the Triggers: Extra Commands
•Modify the Scripts
•Create New Scripts
Configure Load Balancing: Extra Commands
This section describes the commands you need to add to step 8 on page 5 for load
balancer 1 and page 8 for load balancer 2. These extra commands make load balancing act on
SFTP traffic as well as web traffic.
Add a resource pool for SFTP.
add lb respool=sftp selectmethod=roundrobin faillast=no
Add both SFTP resources to the SFTP resource pool. Note that SFTP is FTP encapsulated by
SSHv2 on port 22.
add lb resource=sftp1 ip=192.168.1.1 port=22 respool=sftp
add lb resource=sftp2 ip=192.168.1.2 port=22 respool=sftp
Disable SFTP2. This forces the load balancer to use SFTP1, which is the desired behaviour
because SFTP1 is the preferred server. Later in this configuration, we will create a trigger so
that the load balancer changes to SFTP2 if SFTP1 goes down.
disable lb resource=sftp2 immediately
Add and enable the Virtual Balancer for SFTP traffic.
add lb virtualbalancer=sftp publicip=172.214.1.2 publicport=22
respool=sftp affinity=no
enable lb virtualbalancer=sftp
Note that affinity is turned off. If resource 1 fails, this stops new connections from
automatically trying to use the failed resource.