mDNS (Multicast DNS)

mDNS is a protocol that resolves hostnames to IP addresses within small networks without requiring a conventional DNS server, using multicast queries on the local network. Apple’s implementation is called Bonjour.

What to Know

mDNS/Bonjour enables zero-configuration networking where devices and services automatically advertise their availability without requiring centralized infrastructure or manual configuration. Users simply open the print dialog and see available printers, or browse network shares and find local file servers without typing IP addresses or configuring DNS entries. This dramatically improves user experience in small office and home environments where dedicated DNS servers may not exist or be practical to maintain.

However, mDNS uses multicast traffic that doesn’t route across subnets, limiting its scope to the local network segment. Enterprise networks with VLANs and network segmentation often block or filter multicast traffic for security and performance reasons, breaking Bonjour-based service discovery. IT must balance the convenience of mDNS with network security policies and decide whether to enable multicast across network boundaries or deploy alternative service discovery mechanisms.

Common Scenarios

Enterprise IT: Corporate networks typically restrict mDNS traffic between VLANs for security reasons, preventing cross-subnet service discovery. IT must decide whether to enable mDNS relay/reflection on network switches to allow Bonjour discovery across subnets, or deploy printers and services using traditional DNS and manual configuration. AirPlay-enabled conference room displays often rely on mDNS, requiring IT to ensure multicast traffic flows between user VLANs and display equipment. Print services may use Bonjour for discovery on local subnets while relying on centralized print servers with DNS names for cross-subnet access.

MSP: MSPs supporting small business clients often benefit from mDNS simplicity, as local printers and file shares automatically appear without DNS configuration. Larger client sites with multiple subnets require MSPs to configure network equipment for mDNS relay or implement alternative discovery methods. MSPs should educate clients about mDNS limitations when planning network segmentation and VLAN strategies, as overly aggressive network isolation can break convenient features users expect from Apple devices.

Education: School networks often segment student, staff, and guest VLANs for security, inadvertently breaking mDNS-based printer and AirPlay discovery. Teachers expect to AirPlay to classroom Apple TVs, but network segmentation may prevent device discovery if multicast isn’t properly configured. Education IT must balance security isolation with user experience, often requiring per-building or per-classroom mDNS configuration rather than campus-wide multicast routing. Shared iPad carts in classrooms benefit from mDNS-based automatic printer discovery without requiring per-device print queue configuration.

In Addigy

Addigy-managed devices use mDNS/Bonjour for local service discovery like printer detection and AirPlay functionality, following standard macOS and iOS behavior. Administrators don’t configure mDNS through Addigy directly — it’s a network-level protocol that functions automatically when network infrastructure permits multicast traffic. When troubleshooting service discovery issues, Addigy support can help identify whether network policies are blocking multicast traffic or whether device-level configurations need adjustment.

For organizations deploying printers through Addigy, admins can configure printer profiles that specify printer queues explicitly rather than relying on Bonjour discovery. This approach works across network segments and eliminates dependence on mDNS, providing more predictable printer deployment in complex enterprise networks. Addigy’s device facts collection can reveal network configuration details that may impact mDNS functionality.