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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 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:
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, perform either of the following tasks in interface configuration mode:
| Task | Command |
|---|---|
Set an interface to the requested IPSO classification and authorities. | ip security dedicated level authority [authority...] |
Set an interface to the requested IPSO range of classifications and authorities. | ip security multilevel level1 [authority1...] to level2 authority2 [authority2...] |
Use the no ip security command to reset an interface to its default state.
To specify how IP security options are processed, perform any of the following optional tasks in interface configuration mode:
| Task | Command |
|---|---|
Enable an interface to ignore the authorities field of all incoming packets. | |
Classify packets that have no IPSO with an implicit security label. | ip security implicit-labelling [level authority [authority...]] |
Accept packets on an interface that has an extended security option present. | |
Ensure that all packets leaving the router on an interface contain a basic security option. | ip security add |
Remove any basic security option that might be present on a packet leaving the router through an interface. | |
Prioritize security options on a packet. | |
Treat as valid any packets that have Reserved1 through Reserved4 security levels. |
In order to fully comply with IPSO, the default values for the minor keywords have become complex. Default value usages include the following:
Table 18 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.
We also support a subset of the security features defined in the DNSIX Version 2.1 specification. Specifically, we support 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:
DNSIX Version 2.1 causes slow-switching code.
See the "IPSO Configuration Examples" section at the end of this chapter.
To configure global default setting for extended IPSO, including AESOs, perform the following task in global configuration mode:
| Task | Command |
|---|---|
Configure system-wide default settings. | ip security eso-info source compartment-size default-bit |
To specify the minimum and maximum sensitivity levels for an interface, perform the following tasks in interface configuration mode:
| Task | Command |
|---|---|
Set the minimum sensitivity level for an interface. | ip security eso-min source compartment-bits |
Set the maximum sensitivity level for an interface. | ip security eso-max source compartment-bits |
To specify the extended IPSO sources that are to be treated as AESO sources, perform the following task in interface configuration mode:
| Task | Command |
|---|---|
Specify AESO sources. |
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, perform the following task in global configuration mode:
| Task | Command |
|---|---|
Start the audit writing module. | dnsix-nat source ip-address |
To define and change primary and secondary addresses of the host to receive audit messages, perform the following tasks in global configuration mode:
| Task | Command |
|---|---|
Specify the primary address for the audit trail | dnsix-nat primary ip-address |
Specify the secondary address for the audit trail. | dnsix-nat secondary ip-address |
Specify 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. | dnsix-nat authorized-redirection ip-address |
To specify transmission parameters, perform the following tasks in global configuration mode:
| Task | Command |
|---|---|
Specify the number of records in a packet before it is sent to a collection center. | dnsix-nat transmit-count count |
Specify the number of transmit retries for DMDP. | dnsix-dmdp retries count |
There are two examples in this section:
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 18.
The following commands set up interfaces for the configuration in Figure 18:
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 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 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.
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 configures a Cisco router with HP-UX CMW DNSIX hosts. The following commands should be configured on each LAN interface of the router in order 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.
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