User's Manual

ISG50 User’s Guide 281
CHAPTER 13
Trunks
13.1 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 ISG50'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.
13.1.1 What You Can Do in this Chapter
•Use the Trunk summary screen (Section 13.2 on page 285) 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 13.3 on page 287) to configure which interfaces belong to
each trunk and the load balancing algorithm each trunk uses.
13.1.2 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 ISG50 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 ISG50 balances the WAN traffic load between the connections. If one
interface's connection goes down, the ISG50 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 ISG50 can still send its traffic through another
interface.