Configure a DNS Proxy Object

If your firewall is to act as a DNS proxy, perform this task to configure a DNS Proxy Object. The proxy object can either be shared among all virtual systems or applied to a specific virtual system.
When the firewall is enabled to act as a DNS proxy, evasion signatures that detected crafted HTTP or TLS requests can alert to instances where a client connects to a domain other than the domains specified in the original DNS query. As a best practice, Enable Evasion Signatures after configuring DNS proxy to trigger an alert if crafted requests are detected.
  1. Configure the basic settings for a DNS Proxy object.
    1. Select
      Network
      DNS Proxy
      and
      Add
      a new object.
    2. Verify that
      Enable
      is selected.
    3. Enter a
      Name
      for the object.
    4. For
      Location
      , select the virtual system to which the object applies. If you select
      Shared
      , you must specify at least a
      Primary
      DNS server address, and optionally a
      Secondary
      address.
    5. If you selected a virtual system, for
      Server Profile
      , select a DNS Server profile or else click
      DNS Server Profile
      to configure a new profile. See Configure a DNS Server Profile.
    6. For Inheritance Source, select a source from which to inherit default DNS server settings. The default is
      None
      .
    7. For
      Interface
      , click
      Add
      and specify the interfaces to which the DNS Proxy object applies.
      • If you use the DNS Proxy object for performing DNS lookups, an interface is required. The firewall will listen for DNS requests on this interface, and then proxy them.
      • If you use the DNS Proxy object for a service route, the interface is optional.
  2. (
    Optional
    ) Specify DNS Proxy rules.
    1. On the
      DNS Proxy Rules
      tab,
      Add
      a
      Name
      for the rule.
    2. Turn on caching of domains resolved by this mapping
      if you want the firewall to cache the resolved domains.
    3. For
      Domain Name
      ,
      Add
      one or more domains, one entry per row, to which the firewall compares FQDN queries. If a query matches one of the domains in the rule, the query is sent to one of the following servers to be resolved (depending on what you configured in the prior step):
      • The
        Primary
        or
        Secondary
        DNS Server directly specified for this proxy object.
      • The
        Primary
        or
        Secondary
        DNS Server specified in the DNS Server profile for this proxy object.
      DNS Proxy Rule and FQDN Matching describes how the firewall matches domain names in an FQDN to a DNS proxy rule. If no match is found, default DNS servers resolve the query.
    4. Do one of the following, depending on what you set the
      Location
      to:
      • If you chose a virtual system, select a
        DNS Server profile
        .
      • If you chose
        Shared
        , enter a
        Primary
        and optionally a
        Secondary
        address.
    5. Click
      OK
      .
  3. (
    Optional
    ) Supply the DNS Proxy with static FQDN-to-address entries. Static DNS entries allow the firewall to resolve the FQDN to an IP address without sending a query to the DNS server.
    1. On the
      Static Entries
      tab,
      Add
      a
      Name
      .
    2. Enter the Fully Qualified Domain Name (
      FQDN
      ).
    3. For
      Address
      ,
      Add
      the IP address to which the FQDN should be mapped.
      You can provide additional IP addresses for an entry. The firewall will provide all of the IP addresses in its DNS response and the client chooses which address to use.
    4. Click
      OK
      .
  4. (
    Optional
    ) Enable caching and configure other advanced settings for the DNS Proxy.
    1. On the
      Advanced
      tab, select
      TCP Queries
      to enable DNS queries using TCP.
      • Max Pending Requests
        —Enter the maximum number of concurrent, pending TCP DNS requests that the firewall will support (range is 64-256; default is 64).
    2. For
      UDP Queries Retries
      , enter:
      • Interval (sec)
        —The length of time (in seconds) after which another request is sent if no response has been received (range is 1-30; default is 2).
      • Attempts
        —The maximum number of UDP query attempts (excluding the first attempt) after which the next DNS server is queried (range is 1-30; default is 5.)
    3. Select
      Cache
      to enable the firewall to cache FQDN-to-address mappings that it learns.
      • Select
        Enable TTL
        to limit the length of time the firewall caches DNS resolution entries for the proxy object. Disabled by default.
        • Enter
          Time to Live (sec)
          , the number of seconds after which all cached entries for the proxy object are removed. After the entries are removed, new DNS requests must be resolved and cached again. Range is 60-86,400. There is no default TTL; entries remain until the firewall runs out of cache memory.
      • Cache EDNS Responses
        —Select this if you want the firewall to cache partial DNS responses that are greater than 512 bytes. If a subsequent FQDN for a cached entry arrives, the firewall sends the partial DNS response. If you want full DNS responses (greater than 512 bytes), don’t select this option.
  5. Commit your changes.
    Click
    OK
    and
    Commit
    .

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