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Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring Connection Settings
Information About Connection Settings
TCP Sequence Randomization
Each TCP connection has two ISNs: one generated by the client and one generated by the server. The
ASA randomizes the ISN of the TCP SYN passing in both the inbound and outbound directions.
Randomizing the ISN of the protected host prevents an attacker from predecting the next ISN for a new
connection and potentially hijacking the new session.
TCP initial sequence number randomization can be disabled if required. For example:
•
If another in-line firewall is also randomizing the initial sequence numbers, there is no need for both
firewalls to be performing this action, even though this action does not affect the traffic.
•
If you use eBGP multi-hop through the ASA, and the eBGP peers are using MD5. Randomization
breaks the MD5 checksum.
•
You use a WAAS device that requires the ASA not to randomize the sequence numbers of
connections.
TCP Normalization
The TCP normalization feature identifies abnormal packets that the ASA can act on when they are
detected; for example, the ASA can allow, drop, or clear the packets. TCP normalization helps protect
the ASA from attacks. TCP normalization is always enabled, but you can customize how some features
behave.
The TCP normalizer includes non-configurable actions and configurable actions. Typically,
non-configurable actions that drop or clear connections apply to packets that are always bad.
Configurable actions (as detailed in
“Customizing the TCP Normalizer with a TCP Map” section on
) might need to be customized depending on your network needs.
See the following guidelines for TCP normalization:
•
The normalizer does not protect from SYN floods. The ASA includes SYN flood protection in other
ways.
•
The normalizer always sees the SYN packet as the first packet in a flow unless the ASA is in loose
mode due to failover.
TCP State Bypass
By default, all traffic that goes through the ASA is inspected using the Adaptive Security Algorithm and
is either allowed through or dropped based on the security policy. The ASA maximizes the firewall
performance by checking the state of each packet (is this a new connection or an established
connection?) and assigning it to either the session management path (a new connection SYN packet), the
fast path (an established connection), or the control plane path (advanced inspection). See the
Содержание 5505 - ASA Firewall Edition Bundle
Страница 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Страница 61: ...P A R T 1 Getting Started with the ASA ...
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Страница 218: ...1 56 Cisco ASA Series CLI Configuration Guide Chapter 1 Managing Feature Licenses Feature History for Licensing ...
Страница 219: ...P A R T 2 Configuring High Availability and Scalability ...
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Страница 358: ...1 22 Cisco ASA Series CLI Configuration Guide Chapter 1 Information About Failover Failover Messages ...
Страница 403: ...P A R T 2 Configuring Interfaces ...
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Страница 499: ...P A R T 2 Configuring Basic Settings ...
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Страница 516: ...1 16 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Basic Settings Monitoring DNS Cache ...
Страница 533: ...P A R T 2 Configuring Objects and Access Lists ...
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Страница 558: ...1 4 Cisco ASA Series CLI Configuration Guide Chapter 1 Information About Access Lists Where to Go Next ...
Страница 601: ...P A R T 2 Configuring IP Routing ...
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Страница 632: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Defining Route Maps Feature History for Route Maps ...
Страница 680: ...1 48 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring OSPF Feature History for OSPF ...
Страница 745: ...P A R T 2 Configuring Network Address Translation ...
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Страница 780: ...1 34 Cisco ASA Series CLI Configuration Guide Chapter 1 Information About NAT Where to Go Next ...
Страница 844: ...1 32 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Twice NAT Feature History for Twice NAT ...
Страница 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
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Страница 859: ...1 13 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring AAA Servers and the Local Database Configuring AAA ...
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Страница 981: ...P A R T 2 Configuring Access Control ...
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Страница 994: ...1 12 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Access Rules Feature History for Access Rules ...
Страница 1028: ...1 34 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Management Access Feature History for Management Access ...
Страница 1054: ...1 26 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring AAA Rules for Network Access Feature History for AAA Rules ...
Страница 1060: ...1 6 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Web Cache Services Using WCCP Feature History for WCCP ...
Страница 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
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Страница 1093: ...P A R T 2 Configuring Application Inspection ...
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Страница 1191: ...P A R T 2 Configuring Unified Communications ...
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Страница 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
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Страница 1379: ...P A R T 2 Configuring Advanced Network Protection ...
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Страница 1448: ...1 20 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Threat Detection Configuration Examples for Threat Detection ...
Страница 1474: ...1 18 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Filtering Services Monitoring Filtering Statistics ...
Страница 1475: ...P A R T 2 Configuring Modules ...
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Страница 1504: ...1 28 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring the ASA IPS Module Feature History for the ASA IPS module ...
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Страница 1548: ...1 20 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring the ASA CSC Module Feature History for the CSC SSM ...
Страница 1549: ...P A R T 2 Configuring VPN ...
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Страница 1592: ...1 42 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring IPsec and ISAKMP Supporting the Nokia VPN Client ...
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Страница 1796: ...1 6 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring the PPPoE Client Using Related Commands ...
Страница 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
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Страница 1988: ...1 22 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring Logging Feature History for Logging ...
Страница 2002: ...1 14 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring NetFlow Secure Event Logging NSEL Feature History for NSEL ...
Страница 2036: ...1 34 Cisco ASA Series CLI Configuration Guide Chapter 1 Configuring SNMP Feature History for SNMP ...
Страница 2059: ...P A R T 2 System Administration ...
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Страница 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
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