mDNS Gateway

mDNS is used to advertise and discover service providers on the network.

Service providers announce their services. Clients can passively listen for these announcements or request them using service queries.

Announcements are sent out as multicast to 244.0.0.251 / FF02::FB, UDP port 5353, TTL 1.

Announcements cannot be routed; clients and providers must be on the same VLAN. mDNS/Bonjour Gateway is designed to overcome this limitation.

With mDNS gateway, the WLC becomes a repository for mDNS service providers

Announcements are not bridged across VLANs; the WLC will respond to service queries.

Announcements include the IP address of the service provider; the client connects to the service provider using a normal unicast connection.

mDNS needs to be enabled globally. Without it being enabled, mDNS advertisements are treated as normal multicast.

Master Services DB controls which services could be advertised to clients.

mDNS profiles include services pulled from the master services DB, these determine which SAs are cached and advertised.

mDNS service providers can be discovered on both wired and wireless networks

mDNS Profiles

• assigned to client sessions
• clients can only receive responses for services included in the profile
• Only one profile can be assigned to a client session
• Profiles can be assigned to client sessions by WLAN assignments, local policies, or AAA overrides.

cisco-av-pair=mDNS-profile-name

Configuration

mDNS general shows the master services database, additional services can be added as required.

Learned services are listed on the domain names page. The mDNS browser lists all other services for which advertisements were received, but the service is not in the master services database.

Additional features

• Origin of Service - specify the medium to learn SA, can be per service.
• mDNS APs - allows APs to listen for SAs, uses trunk port AP is connected to if the VLAN if not trunked to the controller.
• Location Specific Services (LSS) - only responds if the client is on the same AP as the SP or one of its neighbors. This only filters out wireless SPs
• Priority MAC - defines a list of SP by MAC that should always be in the SP-DB and not purged out if it runs out of space

Service Policies

• mDNS Polices give fine control over which SAs are sent to which clients.
• Once enabled, all WLC responses are subject to the policy structure.
• The client's mDNS profile still needs to allow the service, polices can then further shrink the list of what can be discovered.
• The default policy will block everything, it only includes devices that are not in another policy.
• Policies are per device and include all services associated with it.
• Can use the “same” keyword for the location.
• OR between Role and User, AND with location.