Identify Sessions That Use Too Much of the On-Chip Packet Descriptor

When a firewall exhibits signs of resource depletion, it might be experiencing an attack that is sending an overwhelming number of packets. In such events, the firewall starts buffering inbound packets. You can quickly identify the sessions that are using an excessive percentage of the on-chip packet descriptor and mitigate their impact by discarding them.
Perform the following task on any hardware-based firewall model (not a VM-Series firewall) to identify, for each slot and dataplane, the on-chip packet descriptor percentage used, the top five sessions using more than two percent of the on-chip packet descriptor, and the source IP addresses associated with those sessions. Having that information allows you to take appropriate action.
  1. View firewall resource usage, top sessions, and session details. Execute the following operational command in the CLI (sample output from the command follows):
    show running resource-monitor ingress-backlogs
    -- SLOT:s1, DP:dp1 -- USAGE - ATOMIC: 92%  TOTAL: 93% TOP SESSIONS:SESS-ID      PCT   GRP-ID   COUNT 6            92%   1        156                   7        1732 SESSION DETAILS SESS-ID PROTO SZONESRC       SPORT  DST       DPORT  IGR-IF    EGR-IF       APP 6    6     trust 55653 80  ethernet1/21 ethernet1/22 undecided
    The command displays a maximum of the top five sessions that each use 2% or more of the on-chip packet descriptor.
    The sample output above indicates that Session 6 is using 92% of the on-chip packet descriptor with TCP packets (protocol 6) coming from source IP address
    • SESS-ID
      —Indicates the global session ID that is used in all other
      show session
      commands. The global session ID is unique within the firewall.
    • GRP-ID
      —Indicates an internal stage of processing packets.
    • COUNT
      —Indicates how many packets are in that GRP-ID for that session.
    • APP
      —Indicates the App-ID extracted from the Session information, which can help you determine whether the traffic is legitimate. For example, if packets use a common TCP or UDP port but the CLI output indicates an APP of
      , the packets are possibly attack traffic. The APP is
      when Application IP Decoders cannot get enough information to determine the application. An APP of
      indicates that Application IP Decoders cannot determine the application; a session of
      APP that uses a high percentage of the on-chip packet descriptor is also suspicious.
    To restrict the display output:
    On a PA-7000 Series model only, you can limit output to a slot, a dataplane, or both. For example:
    show running resource-monitor ingress-backlogs slot s1
    show running resource-monitor ingress-backlogs slot s1 dp dp1
    On PA-5000 Series, PA-5200 Series, and PA-7000 Series models only, you can limit output to a dataplane. For example:
    show running resource-monitor ingress-backlogs dp dp1
  2. Use the command output to determine whether the source at the source IP address using a high percentage of the on-chip packet descriptor is sending legitimate or attack traffic.
    In the sample output above, a single-session attack is likely occurring. A single session (Session ID 6) is using 92% of the on-chip packet descriptor for Slot 1, DP 1, and the application at that point is
    To see whether a session is offloaded or not, use the
    show session id
    operational command in the CLI as shown in the following example. The
    value indicates
    for sessions offloaded or
    for sessions not offloaded.
    If the
    show session id
    command output shows information similar to the following, the output implies that the session has not yet been installed on the PAN-OS firewall. One reason why this can occur is because the traffic is denied due to a configured Security policy rule.
    show session id
    Bad Key: c2s: ‘c2s’
    Bad Key: s2c: ‘s2c’
    index(local): :

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