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Configuring Dynamic Resolution of Hostnames to IP Addresses for RADIUS, Syslog, SNMP, and NTP Servers

To configure dynamic resolution of hostnames:

  1. Include the no-resolve-on-input statement at the [edit system name-resolution] hierarchy level:
    [edit system ]
    no-resolve-on-input;

    The no-resolve-on-input statement enables the JUNOS software to retain the hostname in the router configuration. When this statement is included, the hostnames are resolved only when a router attempts to establish connection with a RADIUS, syslog, SNMP, or NTP server and not at the time of router configuration. If this statement is not included, the hostnames are resolved to IP addresses on input during router configuration. This results in the router configuration file storing only the static IP addresses and not the hostnames.

  2. Configure the following options for the no-resolve-on-input statement:
    [edit system ]
    {
    seconds;
    timeout seconds;
    retries number-of-attempts;
    }
    • cache-refresh-interval seconds—Refresh the cache periodically with the new hostname-to-IP-address mappings from the DNS server entries. Periodically caching the DNS server entries prevents frequent polling of the DNS server. Specify an interval from 15 through 4294967295 seconds.
    • timeout—Specify a timeout value from 1 through 90 seconds for DNS queries.
    • retries—Specify the number of retries from 1 through 10 for a timed-out DNS query.
  3. Configure hostnames on the router for the RADIUS, syslog, SNMP, or NTP servers at the appropriate configuration hierarchy levels in the JUNOS software. For instance, to configure a RADIUS server, include the hostname for the RADIUS server at the [edit system radius-server] hierarchy level:
    [edit system radius-server]
    address; // Hostname instead of IP address for the RADIUS server
  4. Add appropriate DNS entries for the hostname-to-IP address mappings on the DNS server.

You can optionally configure trace operations to be logged by including the following options at the [edit system name-resolution no-resolve-on-input] hierarchy level:

[edit system name-resolution no-resolve-on-input]
traceoptions {
flag all;
flag config;
flag general;
flag updates;
}

To view details of dynamic hostname-to-IP address resolutions, issue the show system name-resolution operational mode command. For more information about this command, see the JUNOS System Basics and Services Command Reference.


Updated: 2009-04-08

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