Multicast Domain Name System - Alcatel-Lucent OmniSwitch 9900 Series Network Configuration Manual

Configuring Access Guardian

Multicast Domain Name System

The Multicast Domain Name System (mDNS) is a resolution service that is used to discover services on a
LAN. Using mDNS allows the resolution of host names to IP addresses within small networks without the
need for a conventional DNS server. The mDNS protocol uses IP multicast User Datagram Protocol
(UDP) packets and is implemented by Apple Bonjour, Avahi (LGPL), and Linux NSS-mDNS. In a BYOD
network, mDNS is leveraged by providing wireless guests and visitors access to network devices, such as
printers.
To resolve a host name, the mDNS client broadcasts a query message asking the host having that name to
identify itself. The target machine then multicasts a message that includes its IP address. All machines in
that subnet will use that information to update their mDNS caches.
For example, the Apple's Bonjour architecture implements the following three fundamental operations to
support zero configuration networking service:
•
Publication (Advertising a service)
•
Discovery (Browsing for available services)
•
Resolution (Translating service instance names to address and port numbers for use)
mDNS Work Flow
The following diagram represents an mDNS work flow setup. The wireless clients connected to Access
point 1 (AP1) or Access Point 2 (AP2) request for the mDNS service offered.
The mDNS feature is enabled on the OmniSwitch to support the mDNS service. A Layer 2 GRE tunnel
interface is configured from the WLAN controller to the OmniSwitch to relay the mDNS messages.
The mDNS message from the Bonjour capable wired service device is encapsulated and relayed from the
OmniSwitch to the configured WLAN controller over the GRE tunnel. The WLAN controller then relays
the mDNS messages received via the OmniSwitch GRE tunnel to the APs over the AP GRE tunnels.
Note. The WLAN controller uses a multicast optimization algorithm and forwards Bonjour response
messages to targeted user devices, instead of all devices on all APs. This limits the unnecessary flooding of
the Bonjour/mDNS traffic to improve the Wi-Fi performance.
OmniSwitch AOS Release 8 Network Configuration Guide
Bring Your Own Devices (BYOD) Overview
December 2017 page 28-127