An external dynamic list is a text file that is hosted on an external web server so that the firewall can import objects—IP addresses, URLs, domains—included in the list and enforce policy. To enforce policy on the entries included in the external dynamic list, you must reference the list in a supported policy rule or profile. As you modify the list, the firewall dynamically imports the list at the configured interval and enforces policy without the need to make a configuration change or a commit on the firewall. If the web server is unreachable, the firewall will use the last successfully retrieved list for enforcing policy until the connection is restored with the web server. To retrieve the external dynamic list, the firewall uses the interface attached to the service route that it uses to access the Palo Alto Updates service.
The firewall supports three types of external dynamic lists:
- IP Address—The firewall typically enforces policy for a source or destination IP address that is defined as a static object on the firewall. If you need agility in enforcing policy for a list of source or destination IP addresses that emerge ad hoc, you can use an external dynamic list of type IP address as a source or destination address object in policy rules, and configure the firewall to deny or allow access to the IP addresses (IPv4 and IPv6 address, IP range and IP subnets) included in the list. The firewall treats an external dynamic list of type IP address as an address object; all the IP addresses included in a list are handled as one address object.
- URL—An external dynamic list of type URL gives you the agility to protect your network from new sources of threat or malware. The firewall handles an external dynamic list with URLs like a custom URL category and you can use this list in two ways:
- As a match criteria in Security policy rules, Decryption policy rules, and QoS policy rules to allow, deny, decrypt, not decrypt, or allocate bandwidth for the URLs in the custom category.
- In a URL Filtering profile where you can define more granular actions, such as continue, alert, or override, before you attach the profile to a Security policy rule.
- Domain—An external dynamic list of type domain allows you to import custom domain names into the firewall to enforce policy using an Anti-Spyware profile. This capability is very useful if you subscribe to third-party threat intelligence and want to protect your network from new sources of threat or malware as soon as you learn of a malicious domain. For each domain you include in the external dynamic list, the firewall creates a custom DNS-based spyware signature so that you can enable DNS sinkholing. The DNS-based spyware signature is of type spyware with medium severity and each signature is namedCustom Malicious DNS Query <domain name>. For details, see Configure DNS Sinkholing for a List of Custom Domains.
On each firewall platform, you can configure a maximum of 30 unique sources for external dynamic lists; these limits are not applicable to Panorama. When using Panorama to manage a firewall that is enabled for multiple virtual systems, if you exceed the limit for the firewall, a commit error displays on Panorama. A source is a URL that includes the IP address or hostname, the path, and the filename for the external dynamic list. The firewall matches the URL (complete string) to determine whether a source is unique.
While the firewall does not impose a limit on the number of lists of a specific type, the following limits are enforced:
- IP address—The PA-5000 Series and the PA-7000 Series firewalls support a maximum of 150,000 total IP addresses; all other platforms support a maximum of 50,000 total IP addresses. No limits are enforced for the number of IP addresses per list. When the maximum supported IP address limit is reached on the firewall, the firewall generates a syslog message. �
- URL and domain—A maximum of 50,000 URLs and 50,000 domains are supported on each platform, with no limits enforced on the number of entries per list.When parsing the list, the firewall skips entries that do not match the list type, and ignores entries that exceed the maximum number supported for the platform.An external dynamic list should not be empty. If you want to stop using the list, remove the reference from the policy rule or profile rather than leave the list empty. If the list is empty, the firewall fails to refresh the list and continues to use the last information it retrieved.
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