1-6
Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring Logging for Access Lists
Managing Deny Flows
Information About Managing Deny Flows
When you enable logging for message 106100, if a packet matches an ACE, the ASA creates a flow entry
to track the number of packets received within a specific interval. The ASA has a maximum of 32 K
logging flows for ACEs. A large number of flows can exist concurrently at any point of time. To prevent
unlimited consumption of memory and CPU resources, the ASA places a limit on the number of
concurrent
deny
flows; the limit is placed on deny flows only (not on permit flows) because they can
indicate an attack. When the limit is reached, the ASA does not create a new deny flow for logging until
the existing flows expire.
For example, if someone initiates a DoS attack, the ASA can create a large number of deny flows in a
short period of time. Restricting the number of deny flows prevents unlimited consumption of memory
and CPU resources.
When you reach the maximum number of deny flows, the ASA issues syslog message 106100:
%ASA|PIX-1-106101: The number of ACL log deny-flows has reached limit
(numbe
r).
The
access-list alert-interval
command sets the time interval for generating syslog message 106001.
Syslog message 106001 alerts you that the ASA has reached a deny flow maximum. When the deny flow
maximum is reached, another syslog message 106001 is generated if at least six seconds have passed
since the last 106001 message was generated.
Licensing Requirements for Managing Deny Flows
The following table shows the licensing requirements for this feature:
Guidelines and Limitations
This section includes the guidelines and limitations for this feature.
Context Mode Guidelines
Supported in single and multiple context mode.
Firewall Mode Guidelines
Supported only in routed and transparent firewall modes.
IPv6 Guidelines
Supports IPv6.
Additional Guidelines and Limitations
The ASA places a limit on the number of concurrent
deny
flows only—not permit flows.
Model
License Requirement
All models
Base License.
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......