External Dynamic List
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External Dynamic List

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External Dynamic List

An external dynamic list is a text file hosted on an external web server so that the firewall can import objects—IP addresses, URLs, domains, International Mobile Equipment Identities (IMEIs), International Mobile Subscriber Identities (IMSIs)—included in the list and enforce policy. To enforce Security policy on entries included in an external dynamic list, you must reference the list in a supported policy rule or profile. When multiple lists are referenced, you can change the order in which the lists are evaluated to ensure the most important external dynamic lists 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 requiring you to make a configuration change or a commit on the firewall. If the web server is unreachable, the firewall uses the last successfully retrieved list to enforce policy until the connection is restored with the web server. In cases where authentication to the external dynamic list fails, the Security policy stops enforcing the external dynamic list. To retrieve the external dynamic list, the firewall uses the interface configured with the
Palo Alto Networks Services
service route.
The firewall retains the last successfully retrieved external dynamic list and continues operating with the most current external dynamic list information until connection is restored with the server hosting the external dynamic list if:
  • You upgrade or downgrade the firewall
  • You reboot the firewall, management plane, or dataplane
  • The server hosting the external dynamic list becomes unreachable
The following warning is displayed when the firewall is unable to connect or otherwise fetch the most current external dynamic list information from the server.
Unable to fetch external list. Using old copy for refresh.
The firewall supports these 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 external dynamic list that uses one of the built-in lists as a source. Because you can’t modify the contents of a predefined list, you can use a predefined list as a source for a different external dynamic list if you want to add or exclude list entries.
  • Predefined URL List
    —This type of external dynamic list contains prepopulated URLs that applications use for background services, such as updates or Certificate Revocation List (CRL) checks, that the firewall can safely exclude from your Authentication policy. Palo Alto Networks revises and maintains this type of external dynamic list, also known as an Authentication Portal Exclude List, through content updates.
  • IP Address
    —The firewall typically enforces policy for a source or destination IP address defined as a static object on the firewall (see Enforce Policy on an External Dynamic List). If you need agility in enforcing policy for a list of source or destination IP addresses that emerge ad hoc, use this external dynamic list type 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) in the list. You can also use an IP address external dynamic list in the source or destination of an SD-WAN policy rule. 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.
  • Domain
    —This type of external dynamic list allows you to import custom domain names into the firewall to enforce policy using an Anti-Spyware profile or SD-WAN policy rule. An external dynamic list in an Anti-Spyware profile is useful if you subscribe to third-party threat intelligence feeds and want to protect your network from new sources of threats 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 configure the firewall to include the subdomains of a specified domain. For example, if your domain list includes paloaltonetworks.com, all lower-level components of the domain name (for example, *.paloaltonetworks.com) will be included in the list. When this setting is enabled, each domain in a given list requires an additional entry, effectively doubling the number of entries used. For details on configuring domain lists, see Configure DNS Sinkholing for a Custom List of Domains.
  • URL
    —This type of external dynamic list 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. You can use this list in two ways:
    • As a match criterion 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 attaching the profile to a Security policy rule (see Use an External Dynamic List in a URL Filtering Profile).
  • Equipment Identity
    —You can reference an external dynamic list of IoT devices defined by International Mobile Equipment Identities (IMEIs) in a Security policy rule that controls traffic for equipment connected to a 5G or 4G network. Refer to the Mobile Network Infrastructure Getting Started for information about configuring Equipment ID security on supported firewall models.
  • Subscriber Identity
    —You can reference an external dynamic list of International Mobile Subscriber Identities (IMSIs) in a Security policy rule that controls traffic for subscribers connected to a 5G or 4G network. Refer to the Mobile Network Infrastructure Getting Started for information about configuring Subscriber ID security on supported firewall models.
On each firewall model, you can add up to 30 custom external dynamic lists with unique sources to enforce policy. The external dynamic list limit does not apply 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, it enforces the following limits:
  • IP address—The PA-3200 Series, PA-5200 Series, and PA-7000 Series firewalls support up to 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 IP address limit is reached, 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-5400 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
    4,000,000
    VM-500, VM-700
    100,000
    2,000,000
    PA-400 Series (excepting the PA-410), PA-850, PA-820, PA-3200 Series, PA-3400 Series
    100,000
    1,000,000
    PA-7000 Series (and appliances upgraded with the PA-7000 20GQ NPC or the PA-7000 20G NPC), VM-300
    100,000
    500,000
    PA-220, PA-410, VM-50, VM-50 (Lite), VM-100, VM-1000-HV
    50,000
    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 exceeding 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
    Objects
    External Dynamic Lists
    and click
    List Capacities
    .
  • An external dynamic list must contain entries. If you want to stop using the list, remove the reference from the policy rule or profile instead of leaving the list blank. If the list contains no entries, 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 external dynamic lists when multiple virtual systems are used. Using individual external dynamic lists with duplicate entries for each virtual system uses more memory, which might overutilize firewall resources.
  • Entry counts in external dynamic lists on firewalls operating multivirtual systems are determined by considering additional factors, such as DAGs, the number of virtual systems, and rulebases. This approach generates a more accurate capacity consumption listing. However, a discrepancy in capacity usage might result after upgrading from PAN-OS 8.x releases.
  • Depending on the features enabled on the firewall, memory usage limits might be exceeded before external dynamic list capacity limits are met due to memory allocation updates. As a best practice, Palo Alto Networks recommends reviewing external dynamic list capacities and, when necessary, removing or consolidating external dynamic lists into shared lists to minimize memory usage.

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