Contents

Configuring mDNS gateway· 1

About mDNS gateway· 1

mDNS network model 1

mDNS gateway functionalities· 2

Protocols and standards· 3

mDNS gateway tasks at a glance· 3

Enabling mDNS gateway· 4

Configuring an mDNS gateway policy· 4

Specifying the permitted service types for entry learning· 4

Specifying trusted mDNS devices· 5

Specifying the source address for mDNS packets· 5

About specifying the source address for mDNS packets· 5

Specifying the source address for mDNS packets in a VLAN· 5

Specifying the source address for mDNS packets in a VSI 5

Enabling mDNS gateway periodic probing· 6

About mDNS gateway periodic probing· 6

Enabling mDNS gateway periodic probing in a VLAN· 6

Enabling mDNS gateway periodic probing in a VSI 6

Display and maintenance commands for mDNS relay· 6

mDNS gateway configuration examples· 7

Example: Configuring mDNS gateway· 7

Troubleshooting mDNS gateway· 9

Failure to receive packets from an mDNS relay· 9

 

Configuring mDNS gateway

About mDNS gateway

A Multicast Domain Name System (mDNS) gateway can be deployed in a large-scale network to enable inter-VLAN or inter-VSI mDNS service discovery. It records a list of available services in the network, responds to service queries from mDNS clients, and performs active mDNS service discovery as well as access control.

mDNS network model

As shown in Figure 1, an mDNS network contains mDNS endpoint devices, mDNS service providers, the mDNS gateway, and mDNS relays.

Figure 1 mDNS networking model

 

mDNS endpoint device

An mDNS endpoint device obtains services from mDNS service providers. Examples are iPhones and iPads.

mDNS service provider

An mDNS service provider provides services for mDNS endpoint devices. Examples are mDNS-capable printers and Apple TVs.

mDNS gateway

The mDNS gateway records available services advertised by mDNS service providers and responds to queries from mDNS endpoint devices. With mDNS gateway enabled, Device B in Figure 1 can act as the mDNS gateway to help mDNS endpoint devices discover mDNS service providers in a different VLAN from the endpoint devices.

mDNS relay

An mDNS relay ensures successful mDNS communication when mDNS endpoint devices and mDNS service providers are in different subnets.

mDNS gateway functionalities

The mDNS gateway provides the following functionalities based on mDNS policies:

·     Reply mDNS queries.

·     Discover mDNS services.

An mDNS gateway policy defines user VLAN or VSI and service VLAN or VSI mappings to ensure that endpoint devices in specific VLANs or VSIs can access only service providers in specific service VLANs or VSIs.

Replying mDNS queries

Upon receiving mDNS queries from mDNS endpoint devices, the gateway checks its service list and sends responses that carry service information to the endpoint devices if matches are found.

Figure 2 Replying mDNS queries

 

As shown in Figure 2, the mDNS gateway replies mDNS queries in a VLAN-separated network as follows:

1.     mDNS service providers broadcast mDNS service responses to notify services.

2.     Upon receiving the responses, the mDNS gateway creates an mDNS service entry that records information such as service instance name and service type.

3.     The mDNS endpoint device sends an mDNS query to the mDNS gateway.

4.     The mDNS gateway searches its service list for the requested service.

¡     If a match is found, the mDNS gateway sends a response to the endpoint device directly.

¡     If no match is found, the mDNS gateway starts service discovery in the corresponding service VLANs of the user VLAN in which the endpoint device resides.

5.     The mDNS endpoint device obtains information about the service provider from the response.

Discovering mDNS services

The mDNS gateway discovers mDNS services by listening to mDNS service responses sent by mDNS service providers and then records information about the services as entries. Service providers can broadcast service responses actively or reply service responses upon requests.

After receiving a query to a service that is not in the service list, the mDNS gateway forwards the query in the corresponding service VLANs of the user VLAN. Upon receiving the query, service providers that provide the service will send responses.

Figure 3 Discovering mDNS services

 

As shown in Figure 3, the mDNS gateway discovers services as follows:

1.     The mDNS gateway receives a query for the printing service from the mDNS endpoint device (iPad).

2.     The mDNS gateway searches its service list for the printing service and no match is found.

3.     The mDNS gateway forwards the mDNS query to the corresponding service VLANs.

4.     Upon receiving the query, the printer sends an mDNS response.

5.     Upon receiving the response, the mDNS gateway records information about the service and sends a response to the mDNS endpoint device.

Protocols and standards

RFC 6762, Multicast DNS

mDNS gateway tasks at a glance

To configure the mDNS gateway, perform the following tasks:

1.     Enabling mDNS gateway

2.     (Optional.) Configuring an mDNS gateway policy

3.     (Optional.) Specifying the permitted service types for entry learning

4.     (Optional.) Specifying trusted mDNS devices

5.     (Optional.) Specifying the source address for mDNS packets

6.     (Optional.) Enabling mDNS gateway periodic probing

Enabling mDNS gateway

1.     Enter system view.

system-view

2.     Enable mDNS gateway.

mdns gateway enable

By default, mDNS gateway is disabled.

Configuring an mDNS gateway policy

Restrictions and guidelines

With mDNS gateway policies configured, the mDNS gateway processes only the queries of mDNS endpoint devices in user VLANs or VSIs configured in the policies.

Procedure

1.     Enter system view.

system-view

2.     Create an mDNS gateway policy and enter its view.

mdns gateway policy policy-name

3.     Specify service VLANs.

service vlan vlan-id-list

By default, no service VLAN is specified.

4.     Specify service VSIs.

service vsi vsi-name

By default, no service VSI is specified.

5.     Specify user VLANs.

user vlan vlan-id-list

By default, no user VLAN is specified.

6.     Specify user VSIs.

user vsi vsi-name

By default, no user VSI is specified.

Specifying the permitted service types for entry learning

About this task

By default, the mDNS gateway can learn all mDNS services of a predefined type, which can be memory-consuming if a large number of service providers exist. You can perform this task to specify the permitted service types that can be learned by the mDNS gateway for the gateway to learn only required services.

Procedure

1.     Enter system view.

system-view

2.     Specify a permitted service type for entry learning.

mdns gateway permit service-type { predefined-service-type | user-defined user-defined-service-type } [ max-entry-count count ]

By default, the mDNS gateway can learn all mDNS services of a pre-defined type.

Specifying trusted mDNS devices

About this task

To prevent security issues and resource waste caused by attacks performed by rogue mDNS devices, you can specify trustworthy mDNS relays as trusted mDNS devices. With trusted devices specified, the mDNS gateway processes only unicast queries from the trusted mDNS devices.

Procedure

1.     Enter system view.

system-view

2.     Specify a trusted mDNS device.

mdns gateway trust device-ip ip-address [ vpn-instance vpn-instance-name ]

By default, no trusted device is specified.

Specifying the source address for mDNS packets

About specifying the source address for mDNS packets

For responses destined for endpoint devices and mDNS queries and probe queries sent within a VLAN or VSI, the default source IP address is the primary IP address of the VLAN interface or VSI interface. If no IP address is configured for the VLAN interface or VSI interface, the mDNS gateway cannot send out the queries.

If the mDNS gateway is connected to a large number of VLANs or VSIs, configuring an IP address to each VLAN interface or VSI interface wastes IP address resources. You can use this command to specify a specific IP address for the mDNS gateway to use.

Specifying the source address for mDNS packets in a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Specify the source address for mDNS packets.

mdns gateway source ip { interface interface-type interface-number | ip-address }

By default, the source IP address is the primary IP address of the VLAN interface.

Specifying the source address for mDNS packets in a VSI

1.     Enter system view.

system-view

2.     Enter VSI view.

vsi vsi-id

3.     Specify the source address for mDNS packets.

mdns gateway source ip { interface interface-type interface-number | ip-address }

By default, the source IP address is the primary IP address of the VSI interface.

Enabling mDNS gateway periodic probing

About mDNS gateway periodic probing

mDNS service providers broadcast their services at network association. For the mDNS gateway to discover services offered by service providers that accessed the network earlier than the gateway, enable mDNS gateway periodic probing.

This feature enables the mDNS gateway to send mDNS probe queries at intervals. Each mDNS service provider sends a response to the gateway after receiving the query. The mDNS gateway can learn the latest service information of all mDNS service providers in the network in a timely manner.

Enabling mDNS gateway periodic probing in a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Enable mDNS gateway periodic probing.

mdns gateway probe interval interval

By default, mDNS gateway periodic probing is disabled.

Enabling mDNS gateway periodic probing in a VSI

1.     Enter system view.

system-view

2.     Enter VSI view.

vsi vsi-id

3.     Enable mDNS gateway periodic probing.

mdns gateway probe interval interval

By default, mDNS gateway periodic probing is disabled.

Display and maintenance commands for mDNS relay

Execute display commands in any view and reset commands in user view.

 

Task	Command
Display mDNS gateway configuration.	display mdns gateway
Display mDNS gateway policy information.	display mdns gateway policy [ policy-name ]
Display information about services learned by the mDNS gateway.	display mdns gateway service { all | predefined-service-type | user-defined user-defined-service-type | vlan vlan-id | vsi vsi-name }
Display mDNS gateway packet statistics.	display mdns gateway statistics
Clear information about services learned by the mDNS gateway.	reset mdns gateway service { all | predefined-service-type | user-defined user-defined-service-type | vlan vlan-id | vsi vsi-name }
Clear mDNS gateway packet statistics.	reset mdns gateway statistics

 

mDNS gateway configuration examples

Example: Configuring mDNS gateway

Network configuration

As shown in Figure 4, a campus network uses mDNS to provide services to both teachers and students. Configure mDNS gateway to allow students to access only the printer and allow teachers to access both the Apple TV and the printer.

Enable mDNS gateway periodic probing for the gateway to update mDNS services in time.

Figure 4 Network diagram

 

Procedure

1.     Enable mDNS gateway.

<Device> system-view

[Device] mdns gateway enable

2.     Create an mDNS gateway policy named student.

[Device] mdns gateway policy student

3.     Specify VLAN 10 as a user VLAN and VLAN 30 as a service VLAN.

[Device-mdns-gateway-policy-student] user vlan 10

[Device-mdns-gateway-policy-student] service vlan 30

[Device-mdns-gateway-policy-student] quit

4.     Create an mDNS gateway policy named teacher.

[Device] mdns gateway policy teacher

5.     Specify VLAN 20 as a user VLAN and VLANs 30 and 40 as service VLANs.

[Device-mdns-gateway-policy-teacher] user vlan 20

[Device-mdns-gateway-policy-teacher] service vlan 30 40

[Device-mdns-gateway-policy-teacher] quit

6.     Permit service types airplay, raop, and printer in entry learning.

[Device] mdns gateway permit service-type airplay

[Device] mdns gateway permit service-type raop

[Device] mdns gateway permit service-type printer

7.     Specify the source address for mDNS packets in VLAN 10.

[Device] vlan 10

[Device-vlan10] mdns gateway source ip 192.168.1.1

[Device-vlan10] quit

8.     Specify the source address for mDNS packets in VLAN 20.

[Device] vlan 20

[Device-vlan20] mdns gateway source ip 192.168.2.1

[Device-vlan20] quit

9.     Enable mDNS gateway periodic probing in VLAN 30 and set the probing interval to 600 seconds.

[Device] vlan 30

[Device-vlan30] mdns gateway probe interval 600

[Device-vlan30] quit

10.     Enable mDNS gateway periodic probing in VLAN 40 and set the probing interval to 600 seconds.

[Device] vlan 40

[Device-vlan40] mdns gateway probe interval 600

[Device-vlan40] quit

Verifying the configuration

# Display mDNS gateway configuration.

[Device] display mdns gateway

mDNS gateway status: Enabled

mDNS gateway source IP:

  VLAN 10: 192.168.1.1

  VLAN 20: 192.168.2.1

mDNS gateway probe is enabled in the following VLANs: 30, 40

mDNS gateway probe is enabled in the following VSIs:

# Display information about services learned by the mDNS gateway.

[Device] display mdns gateway service all

Instance name          Service type VLAN/VSI name TTL        Pro IP

Apple TV               airplay      40            120        TCP 192.168.2.100

Apple TV               raop         40            120        TCP 192.168.2.100

Printer                printer      30            120        TCP 192.168.1.100

 

Total mDNS gateway services: 3

# Verify that students can access only the printer and teachers can access both the Apple TV and the printer.

Troubleshooting mDNS gateway

Failure to receive packets from an mDNS relay

Symptom

The mDNS gateway cannot receive mDNS packets from an mDNS relay.

Analysis

Possible reasons are:

·     The mDNS gateway feature is not enabled.

·     Trusted mDNS devices are configured, but the mDNS relay is not a trusted device.

Solution

To resolve this issue:

1.     Execute the display mdns gateway command to view current configuration. If mDNS gateway is not enabled, execute the mdns gateway enable command to enable this feature.

2.     Execute the display current-configuration command to view trusted mDNS devices. If the mDNS relay is not in the list, execute the mdns gateway trust device-ip command to specify the mDNS relay as a trusted device.