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Sensor Platforms and Modules

The sensors form the workhorses of the Cisco Secure IDS. They constantly monitor network traffic looking for potential attacks. Each sensor checks network traffic looking for a match against one of the attack signatures in its signature database.

Each sensor utilizes two network interfaces. One of these two interfaces monitors network traffic; the other is a command and control interface. All communication with the Director platform occurs over the command and control interface. For further information on basic sensor configuration, refer to Chapter 11, "Sensor Configuration Within CSPM."

When network data triggers a signature, the sensor logs the event and sends an alarm notification to the Director platform. Besides notifying the Director platform, the sensor also has several response options. If the attacker is using a TCP connection, the sensor can send a TCP reset to the connection. To completely shut the attacker off from the network, the sensor can block the attacker's IP address by dynamically updating an ACL on a managed Cisco IOS router (IP blocking). The sensor also can log the IP session that triggered the signature. A final response is for an operator to manually block the host or network that generated the alarms. This manual action takes place on the Director platform.

All sensors are hardware appliances that are tuned for optimum performance. The hardware, including CPU and memory, for each appliance provides optimal IDS performance, while maintaining ease of maintenance. To protect the sensors, the appliance's host operating system must be configured securely. Known security vulnerabilities must be patched, and unneeded services removed.

This section covers the following topics:

  • 4200 Series Sensors
  • IDS module for the Catalyst 6000 family of switches

4200 Series Sensors

The 4200 Series Sensors come in two versions: the IDS-4230 and the IDS-4210. The IDS-4230 is the more powerful of the two sensors and is shown in Figure 4-5. Some of the features of the IDS-4230 are the following:

  • Performance: 100 Mbps
  • Processor: Dual Pentium III 600 MHz
  • Memory: 512 MB
  • Monitoring NIC: FE/SFDDI/DFDDI

Figure 4-5 IDS-4230 Sensor.

The IDS-4210 is a more compact sensor (see Figure 4-6). With the smaller size comes a slimmed down feature set compared to the IDS-4230. The basic features of the IDS-4210 are the following:

  • Performance: 45 Mbps
  • Processor: Single Celeron 566 MHz
  • Memory: 256 MB
  • Monitoring NIC: Ethernet only

Figure 4-6 IDS-4210 Sensor.

Table 4-1 highlights the differences between the 4200 Series Sensors.

Table 4-1 Comparison of 4200 Series Sensors

Sensor Characteristic




100 Mbps

45 Mbps


Dual Pentium III 600 MHz

Single Celeron 566 MHz


512 MB

256 MB

Monitoring network interface cards

10/100 Ethernet

Single-attached FDDI

Dual-attached FDDI

10/100 Ethernet


4 U

1 U

For detailed information on installation of the 4200 Series Sensors, refer to Chapter 7.

IDS Module for the Catalyst 6000 Family of Switches

The IDS Module (IDSM) for the Catalyst 6000 family of switches is designed specifically to address switched environments by integrating IDS functionality directly into the switch. The IDSM receives traffic right off the switch backplane, thereby combining both switching and security functionality into the same chassis (see Figure 4-7).

Figure 4-7 Catalyst 6000 IDS Module.

Similar to the 4200 Series Sensors, IDSM detects unauthorized activity on the network and sends alarms to the Director platform, detailing the event. This sensor resides directly in the switch, capturing data directly from the switch's backplane. Two methods of data capture are the following:

  • Switch port analyzer (SPAN)
  • Virtual LAN access control list

Using a SPAN port enables you to tell the switch to make copies of packets that are destined for certain ports on the switch. VLAN access control lists enable you to define more granular monitoring. This monitoring can be based on specific IP addresses and network services. Furthermore, the IDSM can monitor a full 100 Mbps without impacting switch performance. The monitoring is passive and inspects copies of the packets being monitored. The monitoring is not in the switch-forwarding path.

In addition, the same Director platforms that the 4200 Series Sensors use can monitor IDSM. You can deploy both the 4200 Series Sensors and IDSM on a single network to provide comprehensive coverage of critical subnets, as well as your entire enterprise network.

Some of the major features of IDSM are the following:

  • Fully integrated line card
  • Multi-VLAN visibility
  • Full signature set
  • Common configuration and monitoring
  • 100 Mbps performance
  • No switching performance impact

For detailed information on configuration of IDSM, refer to Chapter 14.

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