For example, if the mDNS gateway functionality is enabled on the router in this figure, then service information
can be sent from one subnet to another and vice-versa. For example, the printer and fax service information
being advertised in the network with IP address 192.0.2.6 are redistributed to the network with IP address
198.51.100.4. The printer and fax service information in the network with IP address 192.0.2.6 is learned by
mDNS-enabled hosts and devices in the other network.
Figure 14: Sample Networking Scenario
Filtering
After configuring the mDNS gateway and subnets, you can filter services that you want to redistribute. While
creating a service list, the
permit
or
deny
command options are used:
•
The
permit
command option allows you to permit or transport specific service list information.
•
The
deny
option allows you to deny service list information that is available to be transported to other
subnets.
You need to include a sequence number when using the
permit
or
deny
command option. The same service
list name can be associated with multiple sequence numbers and each sequence number will be mapped to a
rule.
If no filters are configured, then the default action is to deny service list information to be transported
through the device or interface.
Note
Query is another option provided when creating service lists. You can create queries using a service list. If
you want to browse for a service, then active queries can be used. This function is helpful to keep the records
refreshed in the cache.
Active queries can only be used globally and cannot be used at the interface level.
Note
A service end-point (such as a printer or fax) sends unsolicited announcements when a service starts up. After
that, it sends unsolicited announcements whenever a network change event occurs (such as an interface coming
up or going down). The device always respond to queries.
After creating a service list and using the
permit
or
deny
command options, you can filter using match
statements (commands) based on
service-instance
,
service-type
, or
message-type
(announcement or query).
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Configuring the Service Discovery Gateway
Service Discovery Gateway
