Cisco IOS XR System Security Configuration Guide for the Cisco XR 12000 Series Router, Release 4.2.x
Implementing Lawful Intercept
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Implementing Lawful Intercept


Implementing Lawful Intercept

Lawful intercept is the process by which law enforcement agencies conduct electronic surveillance of circuit and packet-mode communications, authorized by judicial or administrative order. Service providers worldwide are legally required to assist law enforcement agencies in conducting electronic surveillance in both circuit-switched and packet-mode networks.

Only authorized service provider personnel are permitted to process and configure lawfully authorized intercept orders. Network administrators and technicians are prohibited from obtaining knowledge of lawfully authorized intercept orders, or intercepts in progress. Error messages or program messages for intercepts installed in the router are not displayed on the console.

Feature History for Implementing Lawful Intercept



Release 3.7.0

This feature was introduced.

Release 3.8.0

Information erroneously stating that data interception was supported on the AAA RADIUS server was corrected.

Release 4.0.0

Feature information to intercept IPV6 packets was added. Support for intercepting IPV6 packets based on Flow ID mapping, VRF aware matching including 6VPE, mapping packets in 6PE disposition and replicating tag2ip and ip2tag packets was added.

Release 4.2.0

High Availability support for Lawful Intercept was added.

Prerequisites for Implementing Lawful Intercept

You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Lawful intercept implementation also requires that these prerequisites are met:

  • Provisioned router—The router must be already provisioned. For more information, see Cisco IOS XR Getting Started Guide for the Cisco XR 12000 Series Router.


    For the purpose of lawful intercept taps, provisioning a loopback interface has advantages over other interface types.

  • Understanding of SNMP Server commands in Cisco IOS XR software—Simple Network Management Protocol, version 3 (SNMP v3), which is the basis for lawful intercept enablement, is configured using commands described in the module SNMP Server Commands in Cisco IOS XR System Management Command Reference for the Cisco XR 12000 Series Router. To implement lawful intercept, you must understand how the SNMP server functions. For this reason, carefully review the information described in the module Implementing SNMP in Cisco IOS XR System Management Configuration Guide for the Cisco XR 12000 Series Router.
  • Lawful intercept must be explicitly disabled—It is automatically enabled on a provisioned router. However, you should not disable LI if there is an active tap in progress, because this deletes the tap.
  • Management plane configured to enable SNMPv3—Allows the management plane to accept SNMP commands, so that the commands go to the interface (preferably, a loopback) on the router. This allows the mediation device (MD) to communicate with a physical interface.
  • VACM views enabled for SNMP server—View-based access control model (VACM) views must be enabled on the router.
  • Provisioned MD—For detailed information, see the vendor documentation associated with your MD. For a list of MD equipment suppliers preferred by Cisco, see
  • VoIP surveillance-specific requirements
    • Lawful-intercept-enabled call agent—A lawful-intercept-enabled call agent must support interfaces for communications with the MD, for the target of interest to provide signaling information to the MD. The MD extracts source and destination IP addresses and Real-Time Protocol (RTP) port numbers from the Session Description Protocol (SDP) signaling information for the target of interest. It uses these to form an SNMPv3 SET, which is sent to the router acting as the content IAP to provision the intercept for the target of interest. The MD uses the CISCO-TAP2-MIB to set up communications between the router acting as the content IAP, and the MD. The MD uses the CISCO-IP-TAP-MIB to set up the filter for the IP addresses and port numbers to be intercepted and derived from the SDP.
    • Routers to be used for calls by the target number must be provisioned for this purpose through the MD.
    • The MD that has been provisioned with the target number to be intercepted.
  • Data session surveillance-specific requirements
    • Routers to be used by the data target that have been provisioned for this purpose through the MD.
    • The MD that has been provisioned with the user login ID, mac address of the user CPE device, or the DSLAM physical location ID—The IP address is the binding that is most frequently used to identify the target in the network. However, alternative forms of information that uniquely identify the target in the network might be used in some network architectures. Such alternatives include the MAC address and the acct-session-id.
  • The MD can be located anywhere in the network but must be reachable from the content IAP router, which is being used to intercept the target. MD should be reachable ONLY from global routing table and NOT from VRF routing table.

Restrictions for Implementing Lawful Intercept

Lawful intercept does not provide support for these features on Cisco XR 12000 Series Router:

  • IPv6 multicast tapping
  • Per tap drop counter
  • Per interface tapping
  • Replicating a single tap to multiple MDs
  • Tapping of tag packets
  • Tapping L2 flows
  • RTP encapsulation
  • Encryption and integrity checking of replication device

Information About Lawful Intercept Implementation

Cisco lawful intercept is based on service-independent intercept (SII) architecture and SNMPv3 provisioning architecture. SNMPv3 addresses the requirements to authenticate data origin and ensure that the connection from the router to the MD is secure. This ensures that unauthorized parties cannot forge an intercept target.

Lawful intercept offers these capabilities:

  • Voice-over IP (VoIP) and data session intercept provisioning from the MD using SNMPv3
  • Delivery of intercepted VoIP and data session data to the MD
  • SNMPv3 lawful intercept provisioning interface
  • Lawful intercept MIB: CISCO-TAP2-MIB, version 2
  • CISCO-IP-TAP-MIB manages the Cisco intercept feature for IP and is used along with CISCO-TAP2-MIB to intercept IP traffic.
  • User datagram protocol (UDP) encapsulation to the MD
  • Replication and forwarding of intercepted packets to the MD
  • Voice-over IP (VoIP) call intercept, based on any rules configured for received packets.
  • Voice-over IP (VoIP) intercept with LI-enabled call agent
  • Data session call intercept based on IP address

Provisioning for VoIP Calls

Lawful Intercept provisioning for VoIP occurs in these ways:

  • Security and authentication occurs because users define this through SNMPv3.
  • The MD provisions lawful intercept information using SNMPv3.
  • Network management occurs through standard MIBs.

Call Interception

VoIP calls are intercepted in this manner:

  • The MD uses configuration commands to configure the intercept on the call control entity.
  • The call control entity sends intercept-related information about the target to the MD.
  • The MD initiates call content intercept requests to the content IAP router or trunk gateway through SNMPv3.
  • The content IAP router or trunk gateway intercepts the call content, replicates it, and sends it to the MD in Packet Cable Electronic Surveillance UDP format. Specifically, the original packet starting at the first byte of the IP header is prefixed with a four-byte CCCID supplied by the MD in TAP2-MIB. It is then put into a UDP frame with the destination address and port of the MD.
  • After replicated VoIP packets are sent to the MD, the MD then forwards a copy to a law-enforcement-agency-owned collection function, using a recognized standard.

Provisioning for Data Sessions

Provisioning for data sessions occurs in a similar way to the way it does for lawful intercept for VoIP calls. (See Provisioning for VoIP Calls.)

Data Interception

Data are intercepted in this manner:

  • If a lawful intercept-enabled authentication or accounting server is not available, a sniffer device can be used to detect the presence of the target in the network.
    • The MD uses configuration commands to configure the intercept on the sniffer.
    • The sniffer device sends intercept-related information about the target to the MD.
  • The MD initiates communication content intercept requests to the content IAP router using SNMPv3.
  • The content IAP router intercepts the communication content, replicates it, and sends it to the MD in UDP format.
  • Intercepted data sessions are sent from the MD to the collection function of the law enforcement agency, using a supported delivery standard for lawful intercept.

Information About the MD

The MD performs these tasks:

  • Activates the intercept at the authorized time and removes it when the authorized time period elapses.
  • Periodically audits the elements in the network to ensure that:
    • only authorized intercepts are in place.
    • all authorized intercepts are in place.

Lawful Intercept Topology

This figure shows intercept access points and interfaces in a lawful intercept topology for both voice and data interception.

Figure 1. Lawful Intercept Topology for Both Voice and Data Interception

Scale or Performance Improvement

New enhancements introduced on the Cisco XR 12000 Series Router in terms of scalability and performance for lawful intercept are:

  • Increase in number of taps from 50 taps to 100 taps per protocol each for IPv4 and IPv6.
  • Enhancement of interception rate from 25 Kbps to 50 Kbps per slot.

Intercepting IPv6 Packets

This section provides details for intercepting IPv6 packets supported on the Cisco XR 12000 Series Router.

Lawful Intercept Filters

The filters used for classifying a tap are:

  • IP address type
  • Destination address
  • Destination mask
  • Source address
  • Source mask
  • ToS (Type of Service) and ToS mask
  • Protocol
  • Destination port with range
  • Source port with range
  • VRF (VPN Routing and Forwarding)
  • Flow ID

Intercepting IPv6 Packets Based on Flow ID

To further extend filteration criteria for IPv6 packets, an additional support to intercept IPv6 packets based on flow ID has been introduced on the Cisco XR 12000 Series Router. All IPv6 packets are intercepted based on the fields in the IPv6 header which comprises numerous fields defined in IPv6 Header Field Details table:


The field length or payload length is not used for intercepting packets.

Table 1 IPv6 Header Field Details
IPv6 Field Name Field Description Field Length


IPv6 version number.

4 bits

Traffic Class

Internet traffic priority delivery value.

8 bits

Flow ID (Flow Label)

Used for specifying special router handling from source to destination(s) for a sequence of packets.

20 bits

Payload Length

Specifies the length of the data in the packet. When cleared to zero, the option is a hop-by-hop Jumbo payload.

16 bits unassigned

Next Header

Specifies the next encapsulated protocol. The values are compatible with those specified for the IPv4 protocol field.

8 bits

Hop Limit

For each router that forwards the packet, the hop limit is decremented by 1. When the hop limit field reaches zero, the packet is discarded. This replaces the TTL field in the IPv4 header that was originally intended to be used as a time based hop limit.

8 bits unsigned

Source Address

The IPv6 address of the sending node.

16 bytes

Destination Address

The IPv6 address of the destination node.

16 bytes

The flow ID or flow label is a 20 bit field in the IPv6 packet header that is used to discriminate traffic flows. Each flow has a unique flow ID. The filteration criteria to intercept packets matching a particular flow ID is defined in the tap configuration file. From the line card, the intercepted mapped flow IDs are sent to the next hop, specified in the MD configuration file. The intercepted packets are replicated and sent to the MD fom the line card.

Intercepting VRF (6VPE) and 6PE Packets

This section provides information about intercepting VRF aware packets and 6PE packets. Before describing how it works, a basic understanding of 6VPE networks is discussed.

The MPLS VPN model is a true peer VPN model. It enforces traffic separations by assigning unique VPN route forwarding (VRF) tables to each customer's VPN at the provider content IAP router. Thus, users in a specific VPN cannot view traffic outside their VPN.

Cisco XR 12000 Series Router supports intercepting IPv6 packets of the specified VRF ID for 6VPE. To distiguish traffic on VPN, VRFs are defined containing a specific VRF ID. The filter criteria to tap a particular VRF ID is specified in the tap. IPv6 packets are intercepted with the VRF context on both scenarios: imposition (ip2mpls) and disposition (mpls2ip).

The 6PE packets carry IPv6 packets over VPN. The packets do not have a VRF ID. Only IP traffic is intercepted; no MPLS based intercepts are supported. The IPv6 traffic is intercepted at the content IAP of the MPLS cloud at imposition (ip2mpls) and at disposition (mpls2ip).

Intercepting IPv6 packets is also performed for ip2tag and tag2ip packets. Ip2tag packets are those which are converted from IPv6 to Tagging (IPv6 to MPLS), and tag2ip packects are those which are converted from Tagging to IPv6 (MPLS to IPv6) at the provider content IAP router.

Encapsulation Type Supported for Intercepted Packets

Intercepted packets mapping the tap are replicated, encapsulated, and then sent to the MD. IPv4 and IPv6 packets are encapsulated using UDP (User Datagram Protocol) encapsulation. The replicated packets are forwarded to MD using UDP as the content delivery protocol. Both IPv4 and IPv6 MD encapsulations are supported. The encapsulation type (IPv4 or IPv6) depends on the address of MD.

The intercepted packet gets a new UDP header and IPv4 header. Information for IPv4 header is derived from MD configuration. Apart from the IP and UDP headers, a 4 byte channel identifier (CCCID) is also inserted after the UDP header in the packet. After adding the MD encapsulation, if the packet size is above the MTU, the egress LC CPU fragments the packet. Moreover, there is a possibility that the packet tapped is already a fragment. Each tap is associated with only one MD. Cisco XR 12000 Series Router does not support forwarding replicated packets to multiple MDs.


Encapsulation types, such as RTP and RTP-NOR, are not supported.

Per Tap Drop Counter Support

Cisco XR 12000 Series Router line cards provide SNMP server as an interface to export each tap forwarded to MD packet and drop counts. Any intercepted packets that are dropped prior to getting forwarded to the MD due to policer action are counted and reported. The drops due to policer action are the only drops that are counted under per tap drop counters. If a lawful intercept filter is modified, the packet counts are reset to 0.

High Availability for Lawful Intercept

High availability for lawful intercept provides operational continuity of the TAP flows and provisioned MD tables to reduce loss of information due to route processor fail over (RPFO).

To achieve continuous interception of a stream, when RP fail over is detected; MDs are required to re-provision all the rows relating to CISCO-TAP2-MIB, CISCO-IP-TAP-MIB, and CISCO-USER-CONNECTION-TAP-MIB to synchronize database view across RP and MD.


The high availability for lawful intercept is enabled by default from Release 4.2.0 onwards.

Preserving TAP and MD Tables during RP Fail Over

At any point in time, MD has the responsibility to detect the loss of the taps via SNMP configuration process.

After RPFO is completed, MD should re-provision all the entries in the stream tables, MD tables, and IP taps with the same values they had before fail over. As long as an entry is re-provisioned in time, existing taps will continue to flow without any loss.

The following restrictions are listed for re-provisioning MD and tap tables with respect to behavior of SNMP operation on citapStreamEntry, cTap2StreamEntry, cTap2MediationEntry MIB objects:

  • After RPFO, table rows that are not re-provisioned, shall return NO_SUCH_INSTANCE value as result of SNMP Get operation.
  • Entire row in the table must be created in a single configuration step, with exactly same values as before RPFO, and with the rowStatus as CreateAndGo. Only exception is the cTap2MediationTimeout object, that should reflect valid future time.

Replay Timer

The replay timer is an internal timeout that provides enough time for MD to re-provision tap entries while maintaining existing tap flows. It resets and starts on the active RP when RPFO takes place. The replay timer is a factor of number of LI entries in router with a minimum value of 10 minutes.

After replay timeout, interception stops on taps that are not re-provisioned.


In case high availability is not required, MD waits for entries to age out after fail over. MD cannot change an entry before replay timer expiry. It can either reinstall taps as is, and then modify; or wait for it to age out.

How to Configure SNMPv3 Access for Lawful Intercept on the Cisco ASR 9000 Series Router

Perform these procedures in the order presented to configure SNMPv3 for the purpose of Lawful Intercept enablement:

Disabling SNMP-based Lawful Intercept

Lawful Intercept is enabled by default on the Cisco ASR 9000 Series Router.

  • To disable Lawful Intercept, enter the lawful-intercept disable command in global configuration mode.
  • To reenable it, use the no form of this command.

Disabling SNMP-based Lawful Intercept: Example

RP/0/0/CPU0:router# configure
RP/0/0/CPU0:router(config)# lawful-intercept disable


All SNMP-based taps are dropped when lawful intercept is disabled.

Configuring the Inband Management Plane Protection Feature

If MPP was not earlier configured to work with another protocol, then ensure that the MPP feature is also not configured to enable the SNMP server to communicate with the mediation device for lawful interception. In such cases, MPP must be configured specifically as an inband interface to allow SNMP commands to be accepted by the router, using a specified interface or all interfaces.


Ensure this task is performed, even if you have recently migrated to Cisco IOS XR Software from Cisco IOS, and you had MPP configured for a given protocol.

For lawful intercept, a loopback interface is often the choice for SNMP messages. If you choose this interface type, you must include it in your inband management configuration.

For a more detailed discussion of the inband management interface, see the Inband Management Interface.

Enabling the Mediation Device to Intercept VoIP and Data Sessions

The following SNMP server configuration tasks enable the Cisco SII feature on a router running Cisco IOS XR Software by allowing the MD to intercept VoIP or data sessions.


    1.    configure

    2.    snmp-server view view-name ciscoTap2MIB included

    3.    snmp-server view view-name ciscoUserConnectionTapMIB included

    4.    snmp-server group group-name v3auth read view-name write view-name notify view-name

    5.    snmp-server host ip-address traps version 3 auth username udp-port port-number

    6.    snmp-server user mduser-id groupname v3 auth md5 md-password

    7.    Use one of these commands:

    • end
    • commit

    8.    show snmp users

    9.    show snmp group

    10.    show snmp view

      Command or Action Purpose
    Step 1 configure

    RP/0/0/CPU0:router# configure

    Enters global configuration mode.

    Step 2 snmp-server view view-name ciscoTap2MIB included

    RP/0/0/CPU0:router(config)# snmp-server view TapName ciscoTap2MIB included 

    Creates or modifies a view record and includes the CISCO-TAP2-MIB family in the view. The SNMP management objects in the CISCO-TAP2-MIB that controls lawful intercepts are included. This MIB is used by the mediation device to configure and run lawful intercepts on targets sending traffic through the router.

    Step 3 snmp-server view view-name ciscoUserConnectionTapMIB included

    RP/0/0/CPU0:router(config)# snmp-server view TapName ciscoUserConnectionTapMIB included

    Creates or modifies a view record and includes the CISCO-USER-CONNECTION-TAP-MIB family, to manage the Cisco intercept feature for user connections. This MIB is used along with the CISCO-TAP2-MIB to intercept and filter user traffic.

    Step 4 snmp-server group group-name v3auth read view-name write view-name notify view-name

    RP/0/0/CPU0:router(config)# snmp-server group TapGroup v3 auth read TapView write TapView notify TapView 

    Configures a new SNMP group that maps SNMP users to SNMP views. This group must have read, write, and notify privileges for the SNMP view.

    Step 5 snmp-server host ip-address traps version 3 auth username udp-port port-number

    RP/0/0/CPU0:router(config)# snmp-server host traps version 3 auth bgreen udp-port 2555 

    Specifies SNMP trap notifications, the version of SNMP to use, the security level of the notifications, and the recipient (host) of the notifications.

    Step 6 snmp-server user mduser-id groupname v3 auth md5 md-password

    RP/0/0/CPU0:router(config)# snmp-server mduser-id TapGroup v3 auth md5 mdpassword

    Configures the MD user as part of an SNMP group, using the v3 security model and the HMAC MD5 algorithm, which you associate with the MD password.

    • The mduser-id and mdpassword must match that configured on MD. Alternatively, these values must match those in use on the router.
    • Passwords must be eight characters or longer to comply with SNMPv3 security minimums.
    • Minimum Lawful Intercept security level is auth; The noauth option will not work, as it indicates noAuthnoPriv security level. The Lawful Intercept security level must also match that of the MD.
    • Choices other than MD5 are available on the router, but the MD values must match. Most MDs default to or support only MD5.
    Step 7 Use one of these commands:
    • end
    • commit

    RP/0/0/CPU0:router(config)# end


    RP/0/0/CPU0:router(config)# commit

    Saves configuration changes.

    • When you issue the end command, the system prompts you to commit changes:
      Uncommitted changes found, commit them
      before exiting(yes/no/cancel)? [cancel]:
      • Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.
      • Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.
      • Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.
    • Use the commit command to save the configuration changes to the running configuration file, and remain within the configuration session.
    Step 8 show snmp users

    RP/0/0/CPU0:router# show snmp users

    Displays information about each SNMP username in the SNMP user table.

    Step 9 show snmp group

    RP/0/0/CPU0:router# show snmp group

    Displays information about each SNMP group on the network.

    Step 10 show snmp view

    RP/0/0/CPU0:router# show snmp view

    Displays information about the configured views, including the associated MIB view family name, storage type, and status.


    Configuration Example for Inband Management Plane Feature Enablement

    This example illustrates how to enable the MPP feature, which is disabled by default, for the purpose of lawful intercept.

    Configuring the Inband Management Plane Protection Feature: Example

    You must specifically enable management activities, either globally or on a per-inband-port basis, using this procedure. To globally enable inbound MPP, use the keyword all with the interface command, rather than use a particular interface type and instance ID with it.

    RP/0/0/CPU0:router# configure
    RP/0/0/CPU0:router(config)# control-plane
    RP/0/0/CPU0:router(config-ctrl)# management-plane
    RP/0/0/CPU0:router(config-mpp)# inband
    RP/0/0/CPU0:router(config-mpp-inband)# interface loopback0
    RP/0/0/CPU0:router(config-mpp-inband-Loopback0)# allow snmp
    RP/0/0/CPU0:router(config-mpp-inband-Loopback0)# commit
    RP/0/0/CPU0:router(config-mpp-inband-Loopback0)# exit
    RP/0/0/CPU0:router(config-mpp-inband)# exit
    RP/0/0/CPU0:router(config-mpp)# exit
    RP/0/0/CPU0:router(config-ctr)# exit
    RP/0/0/CPU0:router(config)# exit
    RP/0/0/CPU0:router# show mgmt-plane inband interface loopback0
    Management Plane Protection - inband interface
    interface - Loopback0 
            snmp configured - 
                    All peers allowed
    RP/0/0/CPU0:router(config)# commit

    Additional References

    These sections provide references related to implementing lawful intercept.

    Related Documents

    Related Topic

    Document Title

    Lawful Intercept commands

    Cisco IOS XR System Security Command Reference for the Cisco XR 12000 Series Router

    Implementing SNMP

    Cisco IOS XR System Management Configuration Guide for the Cisco XR 12000 Series Router

    SNMP Server commands

    Cisco IOS XR System Management Command Reference for the Cisco XR 12000 Series Router




    A modular, open architecture designed for simple implementation that easily interacts with third-party equipment to meet service provider lawful intercept requirements.

    See RFC-3924 under RFCs.

    An application layer protocol that facilitates the exchange of management information between network devices. Part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite.

    Simple Network Management Protocol Version 3 (SNMPv3)



    MIBs Link

    • CISCO-TAP2-MIB, version 2

    To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http:/​/​​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml





    Cisco Architecture for Lawful Intercept in IP Networks

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