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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 "IP Security Options Commands" chapter 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.
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:
This section describes the following configuration tasks:
Cisco's basic IPSO support provides the following features:
To configure basic IPSO, complete the tasks in the following sections:
To enable IPSO and set security classifications on an interface, use either of the following commands in interface configuration mode:
| Command | Purpose |
|---|---|
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.
To specify how IP security options are processed, use any of the following optional commands in interface configuration mode:
| Command | Purpose |
|---|---|
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 add | 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. |
To fully comply with IPSO, the default values for the minor keywords have become complex. Default value usages include the following:
Table 30 provides a list of all default values.
| Interface Type | Level | Authority | Implicit Labeling | Add IPSO |
|---|---|---|---|---|
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.
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:
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:
To configure global default setting for extended IPSO, including AESOs, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
Router (config)# ip security eso-info source compartment-size default-bit | Configures system-wide default settings. |
To specify the minimum and maximum sensitivity levels for an interface, use the following commands in interface configuration mode:
| Command | Purpose | |
|---|---|---|
Step1 | Router (config-if)# ip security eso-min source compartment-bits | Sets the minimum sensitivity level for an interface. |
Step2 | Router (config-if)# ip security eso-max source compartment-bits | Sets the maximum sensitivity level for an interface. |
To specify the extended IPSO sources that are to be treated as AESO sources, use the following command in interface configuration mode:
| Command | Purpose |
|---|---|
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.
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:
To configure the DNSIX auditing facility, complete the tasks in the following sections:
To enable the DNSIX audit trail facility, use the following command in global configuration mode:
| Command | Purpose |
|---|---|
Router (config)# dnsix-nat source ip-address | Starts the audit writing module. |
To define and change primary and secondary addresses of the host to receive audit messages, use the following commands in global configuration mode:
| Command | Purpose | |
|---|---|---|
Step1 | Router (config)# dnsix-nat primary ip-address | Specifies the primary address for the audit trail. |
Step2 | Router (config)# dnsix-nat secondary ip-address | Specifies the secondary address for the audit trail. |
Step3 | 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. |
To specify transmission parameters, use the following commands in global configuration mode:
| Command | Purpose | |
|---|---|---|
Step1 | Router (config)# dnsix-nat transmit-count count | Specifies the number of records in a packet before it is sent to a collection center. |
Step2 | Router (config)# dnsix-dmdp retries count | Specifies the number of transmit retries for DMDP. |
The following sections provide IPSO configuration examples:
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 39.
The following commands set up interfaces for the configuration in Figure 39:
interface ethernet 0 ip security dedicated confidential genser interface ethernet 1 ip security dedicated secret genser interface ethernet 2 ip security multilevel confidential genser to secret genser
It is possible for the setup to be much more complex.
In the following example, there are devices on Ethernet0 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 Ethernet2 that requires the security option to be the first option present, and this condition also must be specified. The new configuration follows.
interface ethernet 0 ip security dedicated confidential genser ip security implicit-labelling ip security strip interface ethernet 1 ip security dedicated secret genser ip security extended-allowed ! interface ethernet 2 ip security multilevel confidential genser to secret genser ip security extended-allowed ip security first
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.
Posted: Tue Jul 18 13:16:33 PDT 2000
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