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    5. Configure a DNS Proxy Object

    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. 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 to 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 to 30; default is 5.)
      3. Select
        Cache
         to enable the firewall to cache FQDN-to-address mappings that it learns. You must enable
        Cache
         (enabled by default) if this DNS proxy object is used for queries that the firewall generates (that is, under
        Device
        Setup
        Services
        DNS
        , or under
        Device
        Virtual Systems
         and you select a virtual system and
        General
        DNS Proxy
        .
        • 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
          —You must enable this setting if this DNS proxy object is used for queries that the firewall generates (that is, under
          Device
          Setup
          Services
          DNS
          , or under
          Device
          Virtual Systems
           and you select a virtual system and
          General
          DNS Proxy
          .
    5. Commit your changes.
      Click
      OK
       and
      Commit
      .

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