What is a Link Load Balancer in Wide Area Networking?

This article explains what a link load balancer is, in the context of wide area networking and how it gives a central management interface to all the links coming in to an organization and utilize them optimally even in the case of a failure in one of the links. We also look at the advantages and additional features provided by such a link load balancer.

What is a Link Load Balancer?

As consolidated data centres are becoming more popular, the WAN links from the head office and branch offices/ remote sites have become very crucial for business. So, companies are buying bandwidth pipes from different service providers for double the capacity (or less) just to make sure that in case there is an outage of service from one provider, then they have some back-up. Sometimes such back-up links are not used much and the fail over, if the primary link fails is generally not instantaneous.

So, instead of having all the incoming links from the service provider(s) separately terminated and routed to, in to an organisation, a Link Load Balancer is used to terminate all these incoming lines at the gateway level and provide a uniform interface for the systems to connect to it.

Advantages of Link Load Balancers:

If there is an outage with a particular service provider, all the users/ active sessions are seamlessly transferred to the other active lines. The lines provisioned for back-up are also used by the regular users as the link load balancer now provides a uniform interface for all the systems to access any line. That gives some additional bandwidth capacity to the users. Bandwidth allocation, and bandwidth shaping can be done at the WAN gateway level using these link load balancer so that the critical applications always get their share of bandwidth and the chatty non-critical applications do not take up the entire bandwidth. This approach also enables an organization to route certain users to certain lines based on the best performing links to a certain destination (or least cost routing, application type, application priority etc).

Additional Features of a Link Load Balancer:

Certain Link Load Balancers also provide VPN and data compression services from branch to the data centre / HO. They also allow multiple types of WAN links to be connected to them (Like MPLS VPN, Leased Lines, Internet Leased Lines, Broadband connection, 3G Mobile through USB, etc) but this depends on the vendor and the model. Two such appliances can work in High Availability mode – in case one of them fails. Some of them also allow to use each link up to a certain maximum bandwidth (as the charges for some carriers are more when usage exceeds a particular limit). QoS mechanisms help set priority for certain types of traffic (like video, voice etc) which are critical and delay sensitive.

When a link is down, the users are accommodated in the other links and a notification is sent to the administrator via email or cellphone, as most of the Link Load Balancers can integrate with Syslog servers or SNMP network management software’s.

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