Cisco IPS 7.1 Installation Guide download pdf (Page 34)

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Cisco Intrusion Prevention System Appliance Hardware Installation Guide for IPS 7.1

OL-24002-01

Chapter 1 Introducing the Sensor

Supported Sensors

VLAN group subinterfaces associate a set of VLANs with a physical or inline interface. No VLAN can

be a member of more than one VLAN group subinterface. Each VLAN group subinterface is identified

by a number between 1 and 255. Subinterface 0 is a reserved subinterface number used to represent the

entire unvirtualized physical or logical interface. You cannot create, delete, or modify subinterface 0 and

no statistics are reported for it.

An unassigned VLAN group is maintained that contains all VLANs that are not specifically assigned to

another VLAN group. You cannot directly specify the VLANs that are in the unassigned group. When a

VLAN is added to or deleted from another VLAN group subinterface, the unassigned group is updated.

Packets in the native VLAN of an 802.1q trunk do not normally have 802.1q encapsulation headers to

identify the VLAN number to which the packets belong. A default VLAN variable is associated with

each physical interface and you should set this variable to the VLAN number of the native VLAN or to 0.

The value 0 indicates that the native VLAN is either unknown or you do not care if it is specified. If the

default VLAN setting is 0, the following occurs:

• Any alerts triggered by packets without 802.1q encapsulation have a VLAN value of 0 reported in

the alert.

• Non-802.1q encapsulated traffic is associated with the unassigned VLAN group and it is not

possible to assign the native VLAN to any other VLAN group.

Note You can configure a port on a switch as either an access port or a trunk port. On an access port, all traffic

is in a single VLAN is called the access VLAN. On a trunk port, multiple VLANs can be carried over

the port, and each packet has a special header attached called the 802.1q header that contains the VLAN

ID. This header is commonly referred as the VLAN tag. However, a trunk port has a special VLAN called

the native VLAN. Packets in the native VLAN do not have the 802.1q headers attached.

Deploying VLAN Groups

Because a VLAN group of an inline pair does not translate the VLAN ID, an inline paired interface must

exist between two switches to use VLAN groups on a logical interface. For an appliance, you can connect

the two pairs to the same switch, make them access ports, and then set the access VLANs for the two

ports differently. In this configuration, the sensor connects between two VLANs, because each of the

two ports is in access mode and carries only one VLAN. In this case the two ports must be in different

VLANs, and the sensor bridges the two VLANs, monitoring any traffic that flows between the two

VLANs.

You can also connect appliances between two switches. There are two variations. In the first variation,

the two ports are configured as access ports, so they carry a single VLAN. In this way, the sensor bridges

a single VLAN between the two switches.

In the second variation, the two ports are configured as trunk ports, so they can carry multiple VLANs.

In this configuration, the sensor bridges multiple VLANs between the two switches. Because multiple

VLANs are carried over the inline interface pair, the VLANs can be divided into groups and each group

can be assigned to a virtual sensor.

Supported Sensors

Caution Installing the most recent software on unsupported sensors may yield unpredictable results. We do not

support software installed on unsupported platforms.

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Cisco IPS 7.1 Installation Guide Page 34

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Cisco IPS 7.1 Installation Guide Page 34

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