Appendix A Intrusion Detection System Architecture
System Components
A-24
Cisco Intrusion Detection System Appliance and Module Installation and Configuration Guide Version 4.1
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When a host is specified as never block in the NAC configuration, it does not get
translated into permit statements in the ACL. Instead, it is cached by NAC and
used to filter incoming addShunEvent events and addShunEntry control
transactions.
Scenario 2
There are no preblock or postblock ACLs specified, but there is an existing active
ACL. The new ACL is built in the following order:
1.
The allow sensor_ ip_address command (unless the allow sensor shun
command has been configured)
2.
The always block command entries from the configuration
3.
Unexpired blocks from nac.shun.txt
4.
The permit IP any any command
Connection-Based and Unconditional Blocking
NAC supports two types of blocking for hosts and one type of blocking for
networks. Host blocks are connection based or unconditional. Network blocks are
always unconditional.
When a host block is received, NAC checks for the connectionShun attribute on
the host block. If connectionShun is set to true, NAC performs connection
blocking. Any host block can contain optional parameters, such as destination IP
address, source port, destination port, and protocol. For a connection block to take
place, at least the source IP address must be present.
Under the following conditions, NAC forces the block to be unconditional
converting the block from connection type if necessary:
•
A block of any type is active for a specified source IP address
•
A new block of any type is received for that source IP address
•
The new block differs in any of its optional parameters (except the source
port) from the old block
When a block is updated (for example, when a new block arrives while an existing
block for that source IP address or network is already in effect), the remaining
minutes of the existing block is determined. If the time for the new block is less
than or equal to the remaining minutes, no action is taken. Otherwise, the new
block timeout replaces the existing block timeout.
Содержание IDS-4230-FE - Intrusion Detection Sys Fast Ethernet Sensor
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