Services are the construct used to define the properties and destination for traffic traversing the 128T. An example service for a printer can be seen below.
It is common to define a service for every destination of traffic within a network so as to shape traffic and affect policy in a way that assures quality of experience. In deployments of dozens or even hundreds of locations, this may result in duplicate or redundant configuration if a similar service exists at every site. Given the printer example, it is likely that the service configuration would be similar at every location, except for perhaps the
address. The overall configuration can be simplified by using a hostname as the service address instead of an IP address.
This single service template of sorts can now be used for every location, however it requires a DNS server at the location to correctly resolve
local.printer.service to the location-specific address. If it not possible to leverage a DNS server to resolve hostnames, the 128T can be used to define a static mapping to achieve the same result.
A mapping of hostname to a list of addresses can be added to the router configuration which in turn adds entries to
/etc/hosts. 128T will use these addresses as resolutions for the hostnames as if they were directly added to
/etc/hosts or returned by dynamic DNS lookup. The hostname/address mappings are used for all hostnames within the 128T configuration, not only on service addresses.
The service configuration from above, in combination with this router-specific hostname mapping will allow the printer service to be properly defined at each respective location.
show dns resolutions displays whether hostnames provisioned within the 128T configuration have been resolved, either through configuration, leveraging
static-hostname-mapping or manual through the PCLI.
This output from
show dns resolutions is performed with the service configured with an address of
local.printer.service but does not yet have a
As can be seen from the output, the hostname has not been resolved. After the mapping has been configured:
The output of
show dns resolutions will show that the hostname now resolves to a valid address.
set dns resolutions can be used to override or set a value learned from a DNS resolver.
set dns resolution on a hostname resolved by a DNS server, the 128T will no longer attempt to resolve those addresses as static entries do not have a TTL.