Configuring IP Security Options
Cisco provides IP Security Option (IPSO) support as described in RFC 1108. Cisco's implementation is only minimally compliant with RFC 1108 because the Cisco IOS software only accepts and generates a 4-byte IPSO.
IPSO is generally used to comply with the U.S. government's Department of Defense security policy.
For a complete description of IPSO commands, refer to the chapter "IP Security Options Commands" of the Cisco IOS Security Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the "Identifying Supported Platforms" section in the chapter "Using Cisco IOS Software."
In This Chapter
This chapter describes how to configure IPSO for both the basic and extended security options described in RFC 1108. This chapter also describes how to configure auditing for IPSO. This chapter includes the following sections:
•IPSO Configuration Task List
•IPSO Configuration Examples
IPSO Configuration Task List
This section describes the following configuration tasks:
•Configuring Basic IP Security Options
•Configuring Extended IP Security Options
•Configuring the DNSIX Audit Trail Facility
Configuring Basic IP Security Options
Cisco's basic IPSO support provides the following features:
•Defines security level on a per-interface basis
•Defines single-level or multilevel interfaces
•Provides a label for incoming packets
•Strips labels on a per-interface basis
•Reorders options to put any basic security options first
To configure basic IPSO, complete the tasks in the following sections:
•Enabling IPSO and Setting the Security Classifications
•Specifying How IP Security Options Are Processed
Enabling IPSO and Setting the Security Classifications
To enable IPSO and set security classifications on an interface, use either of the following commands in interface configuration mode:
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Router(config-if)# ip security dedicated level authority [authority...] |
Sets an interface to the requested IPSO classification and authorities. |
Router(config-if)# ip security multilevel level1 [authority1...] to level2 authority2 [authority2...] |
Sets an interface to the requested IPSO range of classifications and authorities. |
Use the no ip security command to reset an interface to its default state.
Specifying How IP Security Options Are Processed
To specify how IP security options are processed, use any of the following optional commands in interface configuration mode:
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Router(config-if)# ip security ignore-authorities |
Enables an interface to ignore the authorities field of all incoming packets. |
Router(config-if)# ip security implicit-labelling [level authority [authority...]] |
Classifies packets that have no IPSO with an implicit security label. |
Router(config-if)# ip security extended-allowed |
Accepts packets on an interface that has an extended security option present. |
Router(config-if)# ip security ad |
Ensures that all packets leaving the router on an interface contain a basic security option. |
Router(config-if)# ip security strip |
Removes any basic security option that might be present on a packet leaving the router through an interface. |
Router(config-if)# ip security first |
Prioritizes security options on a packet. |
Router(config-if)# ip security reserved-allowed |
Treats as valid any packets that have Reserved1 through Reserved4 security levels. |
Default Values for Command Keywords
To fully comply with IPSO, the default values for the minor keywords have become complex. Default value usages include the following:
•The default for all of the minor keywords is off, with the exception of implicit-labelling and add.
•The default value of implicit-labelling is on if the interface is "unclassified Genser;" otherwise, it is off.
•The default value for add is on if the interface is not "unclassified Genser;" otherwise, it is off.
Table 67 provides a list of all default values.
Table 67 Default Security Keyword Values
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None |
None |
None |
On |
Off |
Dedicated |
Unclassified |
Genser |
On |
Off |
Dedicated |
Any |
Any |
Off |
On |
Multilevel |
Any |
Any |
Off |
On |
The default value for any interface is "dedicated, unclassified Genser." Note that this implies implicit labeling. This might seem unusual, but it makes the system entirely transparent to packets without options. This is the setting generated when you specify the no ip security interface configuration command.
Configuring Extended IP Security Options
Cisco's extended IPSO support is compliant with the Department of Defense Intelligence Information System Network Security for Information Exchange (DNSIX) specification documents. Extended IPSO functionality can unconditionally accept or reject Internet traffic that contains extended security options by comparing those options to configured allowable values. This support allows DNSIX networks to use additional security information to achieve a higher level of security than that achievable with basic IPSO.
Cisco also supports a subset of the security features defined in the DNSIX version 2.1 specification. Specifically, Cisco supports DNSIX definitions of the following:
•How extended IPSO is processed
•Audit trail facility
There are two kinds of extended IPSO fields defined by the DNSIX 2.1 specification and supported by Cisco's implementation of extended IPSO—Network-level Extended Security Option (NLESO) and Auxiliary Extended Security Option (AESO) fields.
NLESO processing requires that security options be checked against configured allowable information, source, and compartment bit values, and requires that the router be capable of inserting extended security options in the IP header.
AESO is similar to NLESO, except that its contents are not checked and are assumed to be valid if its source is listed in the AESO table.
To configure extended IPSO, complete the tasks in the following sections:
•Configuring Global Default Settings
•Attaching ESOs to an Interface
•Attaching AESOs to an Interface
Configuring Global Default Settings
To configure global default setting for extended IPSO, including AESOs, use the following command in global configuration mode:
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Router(config)# ip security eso-info source compartment-size default-bit |
Configures system-wide default settings. |
Attaching ESOs to an Interface
To specify the minimum and maximum sensitivity levels for an interface, use the following commands in interface configuration mode:
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Step 1 |
Router(config-if)# ip security eso-min source compartment-bits |
Sets the minimum sensitivity level for an interface. |
Step 2 |
Router(config-if)# ip security eso-max source compartment-bits |
Sets the maximum sensitivity level for an interface. |
Attaching AESOs to an Interface
To specify the extended IPSO sources that are to be treated as AESO sources, use the following command in interface configuration mode:
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Router(config-if)# ip security aeso source compartment-bits |
Specifies AESO sources. |
DNSIX version 2.1 causes slow-switching code.
See the "IPSO Configuration Examples" section at the end of this chapter.
Configuring the DNSIX Audit Trail Facility
The audit trail facility is a UDP-based protocol that generates an audit trail of IPSO security violations. This facility allows the system to report security failures on incoming and outgoing packets. The Audit Trail Facility sends DNSIX audit trail messages when a datagram is rejected because of IPSO security violations. This feature allows you to configure organization-specific security information.
The DNSIX audit trail facility consists of two protocols:
•DNSIX Message Deliver Protocol (DMDP) provides a basic message-delivery mechanism for all DNSIX elements.
•Network Audit Trail Protocol provides a buffered logging facility for applications to use to generate auditing information. This information is then passed on to DMDP.
To configure the DNSIX auditing facility, complete the tasks in the following sections:
•Enabling the DNSIX Audit Trail Facility
•Specifying Hosts to Receive Audit Trail Messages
•Specifying Transmission Parameters
Enabling the DNSIX Audit Trail Facility
To enable the DNSIX audit trail facility, use the following command in global configuration mode:
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Router(config)# dnsix-nat source ip-address |
Starts the audit writing module. |
Specifying Hosts to Receive Audit Trail Messages
To define and change primary and secondary addresses of the host to receive audit messages, use the following commands in global configuration mode:
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Step 1 |
Router(config)# dnsix-nat primary ip-address |
Specifies the primary address for the audit trail. |
Step 2 |
Router(config)# dnsix-nat secondary ip-address |
Specifies the secondary address for the audit trail. |
Step 3 |
Router(config)# dnsix-nat authorized-redirection ip-address |
Specifies the address of a collection center that is authorized to change primary and secondary addresses. Specified hosts are authorized to change the destination of audit messages. |
Specifying Transmission Parameters
To specify transmission parameters, use the following commands in global configuration mode:
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Step 1 |
Router(config)# dnsix-nat transmit-count count |
Specifies the number of records in a packet before it is sent to a collection center. |
Step 2 |
Router(config)# dnsix-dmdp retries count |
Specifies the number of transmit retries for DMDP. |
IPSO Configuration Examples
The following sections provide IPSO configuration examples:
•Example 1
•Example 2
•Example 3
Example 1
In this example, three Ethernet interfaces are presented. These interfaces are running at security levels of Confidential Genser, Secret Genser, and Confidential to Secret Genser, as shown in Figure 106.
Figure 106 IPSO Security Levels
The following commands set up interfaces for the configuration in Figure 106:
ip security dedicated confidential genser
ip security dedicated secret genser
ip security multilevel confidential genser to secret genser
It is possible for the setup to be much more complex.
Example 2
In the following example, there are devices on Ethernet 0 that cannot generate a security option, and so must accept packets without a security option. These hosts do not understand security options; therefore, never place one on such interfaces. Furthermore, there are hosts on the other two networks that are using the extended security option to communicate information, so you must allow these to pass through the system. Finally, there also is a host (a Blacker Front End; see the "Configuring X.25 and LABP" chapter of the Cisco IOS Wide-Area Networking Configuration Guide for more information about Blacker emergency mode) on Ethernet 2 that requires the security option to be the first option present, and this condition also must be specified. The new configuration follows.
ip security dedicated confidential genser
ip security implicit-labelling
ip security dedicated secret genser
ip security extended-allowed
ip security multilevel confidential genser to secret genser
ip security extended-allowed
Example 3
This example shows how to configure a Cisco router with HP-UX CMW DNSIX hosts. The following commands should be configured on each LAN interface of the router for two DNSIX hosts to communicate:
ip security multilevel unclassified nsa to top secret nsa
ip security extended allowed
DNSIX hosts do not need to know the router's IP addresses, and DNSIX hosts do not need to set up M6RHDB entries for the routers.
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2007 Cisco Systems, Inc. All rights reserved.