Snort - the de facto standard for intrusion detection/prevention
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Stream4 Format

preprocessor stream4: [noinspect], [asynchronous_link], [keepstats [machine|binary]], \
                      [detect_scans], [log_flushed_streams], [detect_state_problems], \
                      [disable_evasion_alerts], [timeout <seconds>], [memcap <bytes>],  \
                      [max_sessions <num sessions>], [enforce_state], \
                      [cache_clean_sessions <num of sessions>], [ttl_limit <count>], \
                      [self_preservation_threshold <threshold>], \
                      [self_preservation_period <seconds>], \
                      [suspend_threshold <threshold>], [suspend_period <seconds>], \
                      [state_protection], [server_inspect_limit <bytes>], \
                      [enable_udp_sessions], [max_udp_sessions <num sessions>], \
                      [udp_ignore_any]
Option Description
asynchronous_link Uses state transitions based only on one-sided conversation (no tracking of acknowledge/sequence numbers).
cache_clean_sessions <num sessions> Purges this number of least-recently used sessions from the session cache.
detect_scans Turns on alerts for portscan events.
detect_state_problems Turns on alerts for stream events of note, such as evasive RST packets, data on the SYN packet, and out of window sequence numbers.
enforce_state Enforces statefulness so that sessions aren't picked up mid-stream.
keepstats Records session summary information in $<$logdir$>$/session.log. If no options are specified, output is human readable.
log_flushed_streams Log the packets that are part of reassembled stream.
disable_evasion_alerts Turns off alerts for events such as TCP overlap.
timeout <seconds> Amount of time to keep an inactive stream in the state table; sessions that are flushed will automatically be picked up again if more activity is seen. The default value is 30 seconds.
memcap <bytes> Sets the number of bytes used to store packets for reassembly.
max_sessions <num sessions> Sets the maximum number of simultaneous sessions.
noinspect Disables stateful inspection.
ttl_limit <count> Sets the delta value that will set off an evasion alert.
self_preservation_threshold <threshold> Set limit on number of sessions before entering self-preservation mode (only reassemble data on the default ports).
self_preservation_period <seconds> Set length of time (seconds) to remain in self-preservation mode.
suspend_threshold <threshold> Sets limit on number of sessions before entering suspend mode (no reassembly).
suspend_period <seconds> Sets length of time (seconds) to remain in suspend mode.
server_inspect_limit <bytes> Restricts inspection of server traffic to this many bytes until another client request is seen (ie: client packet with data).
state_protection Protects self against DoS attacks.
enable_udp_sessions Enable UDP session tracking.
max_udp_sessions <num sessions> The maximum number of UDP sessions to be tracked. Default is 8192 if UDP sessions are enabled.
udp_ignore_any Ignore traffic on port without port-specific rules. The result of this is that NO rules (include IP only rules) are applied to UDP traffic that has a source/destination port that is listed in a port-specific ruls.


next up previous contents
Next: stream4_reassemble Format Up: Stream4 Previous: Stream4   Contents
Steven Sturges 2007-05-11