You can find the Avahi Settings at Services → Avahi.
Avahi is used to propagate Apple Services to different networks as the broadcast can not cross L2 otherwise.
Before you can use the Avahi it has to be installed. You can install it at System → Addons.
On the page the Avahi can be enabled or disabled.
Interfaces can be specified.
IP Type can be IPv4, IPv6 or both.
Reflection enables the Repetition of mDNS packets across subnets. Allows clients in one subnet to browse for services and clients located in different subnets.
Override Hostname is used for publishing mDNS records. The default is the system hostname.
Override Domain is used for publishing mDNS records. The default is “local”.