Zyxel ZyWALL-USG50 Router Manual PDF (Setup & Configuration Guide)

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ZyWALL USG 50 User’s Guide

271

C

HAPTER

12

Trunks

12.1

Overview

Use trunks for WAN traffic load balancing to increase overall network throughput

and reliability. Load balancing divides traffic loads between multiple interfaces.

This allows you to improve quality of service and maximize bandwidth utilization

for multiple ISP links.

Maybe you have two Internet connections with different bandwidths. You could set

up a trunk that uses spillover or weighted round robin load balancing so time-

sensitive traffic (like video) usually goes through the higher-bandwidth interface.

For other traffic, you might want to use least load first load balancing to even out

the distribution of the traffic load.

Suppose ISP A has better connections to Europe while ISP B has better

connections to Australia. You could use policy routes and trunks to have traffic for

your European branch office primarily use ISP A and traffic for your Australian

branch office primarily use ISP B.

Or maybe one of the ZyWALL's interfaces is connected to an ISP that is also your

Voice over IP (VoIP) service provider. You can use policy routing to send the VoIP

traffic through a trunk with the interface connected to the VoIP service provider

set to active and another interface (connected to another ISP) set to passive. This

way VoIP traffic goes through the interface connected to the VoIP service provider

whenever the interface’s connection is up.

12.1.1

What You Can Do in this Chapter

•

Use the

Trunk

summary screen (

Section 12.2 on page 276

) to configure link

sticking and view the list of configured trunks and which load balancing

algorithm each trunk uses.

•

Use the

Trunk Edit

screen (

Section 12.3 on page 277

) to configure which

interfaces belong to each trunk and the load balancing algorithm each trunk

uses.

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12.1.2

What You Need to Know

•

Add WAN interfaces to trunks to have multiple connections share the traffic

load.

•

If one WAN interface’s connection goes down, the ZyWALL sends traffic through

another member of the trunk.

•

For example, you connect one WAN interface to one ISP and connect a second

WAN interface to a second ISP. The ZyWALL balances the WAN traffic load

between the connections. If one interface's connection goes down, the ZyWALL

can automatically send its traffic through another interface.

You can also use trunks with policy routing to send specific traffic types through

the best WAN interface for that type of traffic.

•

If that interface’s connection goes down, the ZyWALL can still send its traffic

through another interface.

•

You can define multiple trunks for the same physical interfaces.

Link Sticking

You can have the ZyWALL send each local computer’s traffic that is going to the

same destination through a single WAN interface for a specified period of time.

This is useful when a server requires authentication. For example, the ZyWALL

sends a user’s traffic through one WAN IP address when he logs into a server B. If

the user’s subsequent sessions came from a different WAN IP address, the server

would deny them. Here is an example.

Figure 168

Link Sticking

1

LAN user

A

logs into server

B

on the Internet. The ZyWALL uses wan1 to send the

request to server

B

.

LAN

wan2

A

B

1

2

3

wan1

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2

The ZyWALL is using active/active load balancing. So when LAN user

A

tries to

access something on the server, the request goes out through wan2.

3

The server finds that the request comes from wan2’s IP address instead of

wan1’s

IP address and rejects the request.

If link sticking had been configured, the ZyWALL would have still used wan1 to

send LAN user

A

’s request to the server and server would have given the user

A

access.

Load Balancing Algorithms

The following sections describe the load balancing algorithms the ZyWALL can use

to decide which interface the traffic (from the LAN) should use for a session

2

. The

available bandwidth you configure on the ZyWALL refers to the actual bandwidth

provided by the ISP and the measured bandwidth refers to the bandwidth an

interface is currently using.

Least Load First

The least load first algorithm uses the current (or recent) outbound bandwidth

utilization of each trunk member interface as the load balancing index(es) when

making decisions about to which interface a new session is to be distributed. The

outbound bandwidth utilization is defined as the measured outbound throughput

over the available outbound bandwidth.

Here the ZyWALL has two WAN interfaces connected to the Internet. The

configured available outbound bandwidths for WAN 1 and WAN 2 are 512K and

256K respectively.

Figure 169

Least Load First Example

The outbound bandwidth utilization is used as the load balancing index. In this

example, the measured (current) outbound throughput of WAN 1 is 412K and

WAN 2 is 198K. The ZyWALL calculates the load balancing index as shown in the

table below.

2.

In the load balancing section, a session may refer to normal connection-oriented, UDP or SNMP2 traffic.

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Since WAN 2 has a smaller load balancing index (meaning that it is less utilized

than WAN 1), the ZyWALL will send the subsequent new session traffic through

WAN 2.

Weighted Round Robin

The Weighted Round Robin (WRR) algorithm is best suited for situations when the

bandwidths set for the two WAN interfaces are different. Similar to the Round

Robin (RR) algorithm (see

Section 12.4 on page 279

), the The Weighted Round

Robin (WRR) algorithm sets the ZyWALL to send traffic through each WAN

interface in turn. In addition, the WAN interfaces are assigned weights. An

interface with a larger weight gets more of the traffic than an interface with a

smaller weight.

For example, in the figure below, the configured available bandwidth of WAN1 is

1M and WAN2 is 512K. You can set the ZyWALL to distribute the network traffic

between the two interfaces by setting the weight of wan1 and wan2 to 2 and 1

respectively. The ZyWALL assigns the traffic of two sessions to wan1 for every

session's traffic assigned to wan2.

Figure 170

Weighted Round Robin Algorithm Example

Spillover

The spillover load balancing algorithm sends network traffic to the first interface in

the trunk member list until the interface’s maximum allowable load is reached,

then sends the excess network traffic of new sessions to the next interface in the

trunk member list. This continues as long as there are more member interfaces

and traffic to be sent through them.

Suppose the first trunk member interface uses an unlimited access Internet

connection and the second is billed by usage. Spillover load balancing only uses

the second interface when the traffic load exceeds the threshold on the first

Table 73

Least Load First Example

INTERFACE

OUTBOUND

LOAD BALANCING INDEX

(M/A)

AVAILABLE (A)

MEASURED (M)

WAN 1

512 K

412 K

0.8

WAN 2

256 K

198 K

0.77

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interface. This fully utilizes the bandwidth of the first interface to reduce Internet

usage fees and avoid overloading the interface.

In this example figure, the upper threshold of the first interface is set to 800K.

The ZyWALL sends network traffic of new sessions that exceed this limit to the

secondary WAN interface.

Figure 171

Spillover Algorithm Example

Finding Out More

•

See

Section 6.5.5 on page 97

for related information on the

Trunk

screens.

•

See

Section 7.3 on page 115

for an example of how to configure load balancing.

•

See

Section 12.4 on page 279

for more background information on trunks.

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