External Dynamic List
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. When multiple lists are referenced, you can prioritize the order of evaluation to make sure the most important EDLs are committed before capacity limits are reached. 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, but only if the list is not secured with SSL. To retrieve the external dynamic list, the firewall uses the interface configured with the Palo Alto Networks Services service route.
The firewall supports four types of external dynamic lists:
- Predefined IP Address—A predefined IP address list is a type of IP address list that refers to the built-in, dynamic IP lists with fixed or “predefined” contents. These Built-in External Dynamic Lists—for bulletproof hosting providers, known malicious, and high-risk IP addresses—are automatically added to your firewall if you have an active Threat Prevention license. A predefined IP address list can also refer to an EDL that uses one of the built-in lists as a source. Because you can’t modify the contents of a predefined list, you might use one as a source for a different EDL if you want to add or exclude list entries.
- IP Address—The firewall typically enforces policy for a source or destination IP address that is defined as a static object on the firewall (see Use an External Dynamic List of Type IP or Predefined IP as a Source or Destination Address Object in a Security Policy Rule.) 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 (see Use an External Dynamic List in a URL Filtering Profile).
- 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 feeds 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 named Custom Malicious DNS Query <domain name>. You can also specify the firewall to include the subdomains of a specifed domain. For example, if your domain list includes paloaltonetworks.com, all lower level components of the domain name (e.g., *.paloaltonetworks.com) will also be included as part of the list. When this setting is enabled, each domain in a given list requires an additional entry, effectively doubling the number of entries used by the list. For details on configuring domain lists, see Configure DNS Sinkholing for a List of Custom Domains.
On each firewall model, you can add a maximum of 30 custom EDLs with unique sources to enforce policy. The external dynamic list limit is 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-5200 Series and the PA-7000 Series firewalls support a maximum of 150,000 total IP addresses; all other models 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. The IP addresses in predefined IP address lists do not count toward the limit.
- URL and domain—The maximum number of URLs and domains supported varies by model. No limits are enforced for the number of URL or domain entries per list. Refer to the following table for specifics on your model:Model
URL List Entry Limits Domain List Entry Limits PA-5200 Series, PA-7000 Series (upgraded with the PA-7000 20GXM NPC, PA-7000 20GQXM NPC, or the PA-7000 100G NPC).PA-7000 appliances with mixed NPCs only support the standard capacities. 250,000 4,000,000VM-500, VM-700100,000 2,000,000PA-850, PA-820, PA-3200 Series100,000 1,000,000PA-7000 Series (and appliances upgraded with the PA-7000 20GQ NPC or the PA-7000 20G NPC), VM-300100,000 500,000PA-220, VM-50, VM-50 (Lite), VM-100, VM-1000-HV, PA-3000 Series50,000 50,000
List entries only count toward the firewall limits if they belong to an external dynamic list that is referenced in policy.
- 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 model. To ensure that the entries do not exceed the limit, check the number of entries currently used in policy. Select ObjectsExternal Dynamic Lists and click List Capacities.
- 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.
- As a best practice, Palo Alto Networks recommends using shared EDLs when multiple virtual systems are used. Using individual EDLs with duplicate entries for each virtual system uses more memory, which might over-utilize firewall resources.
- EDL entry counts on firewalls operating multi-virtual systems take additional factors into account (such as DAGs, number of vsys, rules bases) to generate a more accurate capacity consumption listing. This might result in a discrepancy in capacity usage after upgrading from PAN-OS 8.x releases.
- Depending on the features enabled on the firewall, memory usage limits might be exceeded before EDL capacity limits are met due to memory allocation updates. As a best practice, Palo Alto Networks recommends reviewing EDL capacities and, when necessary, removing or consolidating EDLs into shared lists to minimize memory usage.
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