Specifications

30 Barracuda Link Balancer Administrator’s Guide
• Use the tools on the Advanced > Troubleshooting page, ping the remote gateway and perform
other diagnostics on the network connection.
Configuring the DNS Server for Inbound Load Balancing
Configure the Barracuda Link Balancer as an authoritative DNS Server for your domain or domains
to achieve inbound link load balancing.
This section covers the following topics:
Introduction........................................................................................ 30
DNS Records Time to Live................................................................. 30
Recommended Deployment ................................................................ 31
Split DNS ........................................................................................... 31
DNS Zone Transfer Blocking ............................................................. 31
Becoming an Authoritative DNS Host ............................................... 31
If You Add a WAN Link After the Domains are Created ................... 34
Zones and Domains ........................................................................... 34
DNS Records...................................................................................... 35
Introduction
The Barracuda Link Balancer can act as an authoritative DNS server, returning definitive answers to
DNS queries about domain names installed in its configuration. This allows you to define one or more
domains that are accessible via more than one WAN link. When asked to resolve a host, the Barracuda
Link Balancer will return one of the IP addresses of the available WAN links. This provides two
benefits:
• Failover - If one WAN link goes down, the domain is still available via one of the other WAN
links.
• Incoming link balancing - Incoming traffic to the domain will be spread across all links that you
configure for that domain.
Only WAN links with static IP addresses can be advertised to respond to DNS queries. However, you
can accept traffic on any of your WAN links for a domain configured on the Barracuda Link Balancer.
DNS resource records describe the hosts and name servers and other attributes of the domain.
Following the instructions provided here and using the user interface of the Barracuda Link Balancer,
you can create the records that describe the domain or domains that are hosted on the LAN side of the
Barracuda Link Balancer. The supported DNS resource records are described in the section DNS
Records on page 35
DNS Records Time to Live
As already mentioned, making the Barracuda Link Balancer the authoritative DNS server for the
domains that are behind it increases the availability of your hosted servers. When asked for the IP
address of a hostname, the Barracuda Link Balancer returns a DNS A record that contains the IP
address of one of your WAN links. Every DNS record has a TTL (Time to Live) value. TTL is the
length of time that the DNS record may be cached. For most DNS records, two days is a typical and
acceptable value. However, A records should have a very short TTL - we recommend 30 seconds. If
a WAN link fails, its address will no longer be returned, so the inbound traffic to this host will not be