Specifications

Chapter 1: Introduction 3
Link Management
The Barracuda Link Balancer can manage links that have static or dynamic (DHCP) IP addresses and
can authenticate using PPPoE.
Aggregating Link Bandwidth
The Barracuda Link Balancer automatically aggregates Internet bandwidth from multiple links to the
same or diverse sources. Administrators can choose multiple links to the same or different ISPs for
the purposes of consolidating access to affordable Internet bandwidth.
Any single session (e.g. a TCP stream) has at most only the bandwidth from any one WAN link. One
computer may have more than one session if it is connected to more than one remote site.
Link Failover
The Barracuda Link Balancer regularly checks the health of each Internet link and only uses the
available links. If it detects a link failure, the failed link is removed from link balancing. When the
failed link becomes available again, the Barracuda Link Balancer will resume using that link. All of
this happens without administrator intervention.
If a link fails, existing sessions on that link will be disconnected. Clients who were using the failed
link will be able to reconnect quickly to their destination using another available link rather than
having to wait for the original link to be restored.
Outbound Link Load Balancing
When traffic from a client IP address going to a new destination IP address is detected, the Barracuda
Link Balancer selects which link to use. It calculates the available capacity for each link based on
uplink speed and current usage and uses the link with the largest available capacity. If needed, you
can create outbound routing rules to override this behavior.
Inbound Link Balancing and Failover
The Barracuda Link Balancer uses authoritative DNS to direct incoming connections to a WAN link.
When an external user accesses a Web site, for example, that is hosted behind the Barracuda Link
Balancer, a DNS request is sent to the Barracuda Link Balancer for the IP address of the site. The
Barracuda Link Balancer returns the IP address of the site which directs the traffic to a WAN link.
When determining which IP address to return, the available capacity for each link based on configured
speed and current usage is calculated. The link with the largest available capacity is returned so that
adaptive inbound load balancing is achieved. Also, if a link is found to have failed, the address for
that link is not returned until it becomes available again.
In order to accomplish this, the Barracuda Link Balancer acts as an authoritative DNS server for the
domains or sub-domains that you host. You can create DNS records on the Barracuda Link Balancer
to identify your domain and to map that domain to multiple externally accessible IP addresses.