Subsections

1.7 Basic Output

Snort does a lot of work and outputs some useful statistics when it is done. Many of these are self-explanatory. The others are summarized below. This does not include all possible output data, just the basics.

1.7.1 Timing Statistics

This section provides basic timing statistics. It includes total seconds and packets as well as packet processing rates. The rates are based on whole seconds, minutes, etc. and only shown when non-zero.

Example:

===============================================================================
Run time for packet processing was 175.856509 seconds
Snort processed 3716022 packets.
Snort ran for 0 days 0 hours 2 minutes 55 seconds
   Pkts/min:      1858011
   Pkts/sec:        21234
===============================================================================

1.7.2 Packet I/O Totals

This section shows basic packet acquisition and injection peg counts obtained from the DAQ. If you are reading pcaps, the totals are for all pcaps combined, unless you use -pcap-reset, in which case it is shown per pcap.

Outstanding indicates how many packets are buffered awaiting processing. The way this is counted varies per DAQ so the DAQ documentation should be consulted for more info.
Filtered packets are not shown for pcap DAQs.
Injected packets are the result of active response which can be configured for inline or passive modes.

Example:

===============================================================================
Packet I/O Totals:
   Received:      3716022
   Analyzed:      3716022 (100.000%)
    Dropped:            0 (  0.000%)
   Filtered:            0 (  0.000%)
Outstanding:            0 (  0.000%)
   Injected:            0
===============================================================================

1.7.3 Protocol Statistics

Traffic for all the protocols decoded by Snort is summarized in the breakdown section. This traffic includes internal "pseudo-packets" if preprocessors such as frag3 and stream5 are enabled so the total may be greater than the number of analyzed packets in the packet I/O section.

Disc counts are discards due to basic encoding integrity flaws that prevents Snort from decoding the packet.
Other includes packets that contained an encapsulation that Snort doesn't decode.
S5 G 1/2 is the number of client/server sessions stream5 flushed due to cache limit, session timeout, session reset.

Example:

===============================================================================
Breakdown by protocol (includes rebuilt packets):
        Eth:      3722347 (100.000%)
       VLAN:            0 (  0.000%)
        IP4:      1782394 ( 47.884%)
       Frag:         3839 (  0.103%)
       ICMP:        38860 (  1.044%)
        UDP:       137162 (  3.685%)
        TCP:      1619621 ( 43.511%)
        IP6:      1781159 ( 47.850%)
    IP6 Ext:      1787327 ( 48.016%)
   IP6 Opts:         6168 (  0.166%)
      Frag6:         3839 (  0.103%)
      ICMP6:         1650 (  0.044%)
       UDP6:       140446 (  3.773%)
       TCP6:      1619633 ( 43.511%)
     Teredo:           18 (  0.000%)
    ICMP-IP:            0 (  0.000%)
      EAPOL:            0 (  0.000%)
    IP4/IP4:            0 (  0.000%)
    IP4/IP6:            0 (  0.000%)
    IP6/IP4:            0 (  0.000%)
    IP6/IP6:            0 (  0.000%)
        GRE:          202 (  0.005%)
    GRE Eth:            0 (  0.000%)
   GRE VLAN:            0 (  0.000%)
    GRE IP4:            0 (  0.000%)
    GRE IP6:            0 (  0.000%)
GRE IP6 Ext:            0 (  0.000%)
   GRE PPTP:          202 (  0.005%)
    GRE ARP:            0 (  0.000%)
    GRE IPX:            0 (  0.000%)
   GRE Loop:            0 (  0.000%)
       MPLS:            0 (  0.000%)
        ARP:       104840 (  2.817%)
        IPX:           60 (  0.002%)
   Eth Loop:            0 (  0.000%)
   Eth Disc:            0 (  0.000%)
   IP4 Disc:            0 (  0.000%)
   IP6 Disc:            0 (  0.000%)
   TCP Disc:            0 (  0.000%)
   UDP Disc:         1385 (  0.037%)
  ICMP Disc:            0 (  0.000%)
All Discard:         1385 (  0.037%)
      Other:        57876 (  1.555%)
Bad Chk Sum:        32135 (  0.863%)
    Bad TTL:            0 (  0.000%)
     S5 G 1:         1494 (  0.040%)
     S5 G 2:         1654 (  0.044%)
      Total:      3722347
===============================================================================

1.7.4 Snort Memory Statistics

On systems with mallinfo (3), you will see additional statistics. Check the man page of mallinfo for details

Example:

===============================================================================
Memory usage summary:
  Total non-mmapped bytes (arena):       415481856
  Bytes in mapped regions (hblkhd):      409612288
  Total allocated space (uordblks):      92130384
  Total free space (fordblks):           323351472
  Topmost releasable block (keepcost):   3200
===============================================================================

1.7.5 Actions, Limits, and Verdicts

Action and verdict counts show what Snort did with the packets it analyzed. This information is only output in IDS mode (when snort is run with the -c <conf> option).

Alerts is the number of alert, and block actions processed as determined by the rule actions. Here block includes block, drop, and reject actions.

Limits arise due to real world constraints on processing time and available memory. These indicate potential actions that did not happen:

Match Limit counts rule matches were not processed due to the config detection: max_queue_events setting. The default is 5.
Queue Limit counts events couldn't be stored in the event queue due to the config event_queue: max_queue setting. The default is 8.
Log Limit counts events were not alerted due to the config event_queue: log setting. The default is 3.
Event Limit counts events not alerted due to event_filter limits.
Alert Limit counts events were not alerted because they already were triggered on the session.

Verdicts are rendered by Snort on each packet:

Allow = packets Snort analyzed and did not take action on.
Block = packets Snort did not forward, e.g. due to a block rule. "Block" is used instead of "Drop" to avoid confusion between dropped packets (those Snort didn't actually see) and blocked packets (those Snort did not allow to pass).
Replace = packets Snort modified, for example, due to normalization or replace rules. This can only happen in inline mode with a compatible DAQ.
Whitelist = packets that caused Snort to allow a flow to pass w/o inspection by any analysis program. Like blacklist, this is done by the DAQ or by Snort on subsequent packets.
Blacklist = packets that caused Snort to block a flow from passing. This is the case when a block TCP rule fires. If the DAQ supports this in hardware, no further packets will be seen by Snort for that session. If not, snort will block each packet and this count will be higher.
Ignore = packets that caused Snort to allow a flow to pass w/o inspection by this instance of Snort. Like blacklist, this is done by the DAQ or by Snort on subsequent packets.
Int Blklst = packets that are GTP, Teredo, 6in4 or 4in6 encapsulated that are being blocked. These packets could get the Blacklist verdict if config tunnel_verdicts was set for the given protocol. Note that these counts are output only if non-zero. Also, this count is incremented on the first packet in the flow that alerts. The alerting packet and all following packets on the flow will be counted under Block.
Int Whtlst = packets that are GTP, Teredo, 6in4 or 4in6 encapsulated that are being allowed. These packets could get the Whitelist verdict if config tunnel_verdicts was set for the given protocol. Note that these counts are output only if non-zero. Also, this count is incremented for all packets on the flow starting with the alerting packet.

Example:

===============================================================================
Action Stats:
     Alerts:            0 (  0.000%)
     Logged:            0 (  0.000%)
     Passed:            0 (  0.000%)
Limits:
      Match:            0
      Queue:            0
        Log:            0
      Event:            0
      Alert:            0
Verdicts:
      Allow:      3716022 (100.000%)
      Block:            0 (  0.000%)
    Replace:            0 (  0.000%)
  Whitelist:            0 (  0.000%)
  Blacklist:            0 (  0.000%)
     Ignore:            0 (  0.000%)
===============================================================================