# Patent

## Title
Network device having service card for lawful intercept and monitoring of packet flows

## Abstract

A network device comprises a service card (e.g., a lawful intercept (LI) service card) executing a communication protocol to receive, from one or more sources (e.g., law enforcement agents), intercept information specifying at least one destination and criteria for matching one or more packet flows. The network device further includes a network interface card to receive a packet from a network, and a control unit to provide the packet from the interface card to the LI service card. The LI service card executes a flow match detection module that, when the packet matches the criteria of the intercept information, forwards the packet to the destination specified by the intercept information. The network device may provide real-time intercept and relaying of specified network-based communications. Moreover, the techniques described herein allow LEAs to tap packet flows with little delay after specifying intercept information, e.g., within 50 milliseconds, even under high-volume networks.

## Background
This application claims the benefit of U.S. Provisional Application No. 60/799,872, filed May 12, 2006, the entire content of which is incorporated herein by reference.


TECHNICAL FIELD
The invention relates to computer networks and, more particularly, to techniques for initiating lawful intercept of traffic flows within computer networks.
BACKGROUND
A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
The packets are communicated according to a communication protocol that defines the format of the packet. A typical packet, for example, includes a header carrying source and destination information, as well as a payload that carries the actual data. The de facto standard for communication in conventional packet-based networks, including the Internet, is the Internet Protocol (IP).
In some cases, a Law Enforcement Agency (LEA) may require the system administrator to mirror network traffic flowing to and from a designated network user. The original network traffic is routed across the network as usual while a mirrored version of the network traffic is forwarded for analysis. The term “lawful intercept” is used to describe the process by which LEAs conduct electronic surveillance of packet-based communications as authorized by a judicial or administrative order. Increasingly, legislation and regulations are being adopted that require public and private service providers to support authorized electronic surveillance. This increase is due in part to the increased use of computer networks for real-time voice communications using, for example, Voice over IP (VoIP).
Conventionally, lawful intercept of a network service, such as VoIP, has been enabled and managed by the system administrator interacting with a command line interface presented by a network device providing the network service. This technique may become difficult as the number of network services and respective devices increase. Delay and other difficulties may arise as both the number of filtering criteria entered and the number packet flows being monitored increases. For example, an undesirably long delay may occur from the time a new filtering criterion is entered until packets meeting the criterion may be captured.
SUMMARY
In general, a network monitor is described that utilizes one or more lawful intercept service cards to provide real-time intercept and relaying of specified network-based communications, even under high-volume traffic rates. The techniques are described herein by way of example to lawful intercept (LI) service cards that can monitor and distribute targeted network communications to law enforcement agents under high traffic rates, even core traffic rates of the Internet, including OC-3, OC-12, OC-48, and higher rates. Moreover, the techniques described herein allow control sources (such as law enforcement agents) to tap new or current packet flows within an extremely small period of time after specifying intercept information, e.g., within 50 milliseconds, even under high-volume networks. Further, the techniques can readily be applied in large networks that may have one or more million of concurrent packet flows, and where law enforcement agents may define hundreds of thousands of filter entries in order to target specific communications.
Although described with respect to lawful intercept, the technique can readily be applied to other environments where multiple control sources need to independently monitor and intercept particular packet flows. Examples of other such environments include distributed system administration, accounting and billing systems, network traffic analysis, network attack detection, intrusion detection and the like.
In one embodiment, a network device comprises a lawful intercept (LI) service card executing a communication protocol to receive, from one or more law enforcement agents (LEAs), intercept information specifying at least one destination and criteria for matching one or more packet flows. The network device further comprises a network interface card to receive a packet from a network, and a control unit to provide the packet from the interface card to the LI service card. The LI service card executes a flow match detection module that, when the packet matches the criteria of the intercept information, forwards the packet to the destination specified by the intercept information.
In another embodiment, a lawful intercept (LI) service card comprises an electrical interface for insertion within a slot of a network device, and a law enforcement agents (LEAs) interface executing within the LI service card for receiving intercept information specifying one or more flow criteria. A flow match detection module executes within the LI service card to receive a packet from the network device via the electrical interface. The flow match detection module determines whether the packet matches the flow criteria of the intercept information and, when the packet matches the flow criteria of the intercept information, forwards the packet to a destination associated with the LEAs.
In another embodiment, a method comprises receiving, with a lawful intercept (LI) service card of a network device, intercept information from one or more law enforcement agent (LEAs), wherein the intercept information specifies at least one destination and at least one criteria for matching one or more packet flows. The method further comprises receiving a packet from a network via an interface card of a network device; and determining, with the LI service card, whether the packet matches the flow criteria of the intercept information. The method further comprises, when the packet matches the flow criteria of the intercept information, outputting the matching packet from the LI service card to the destination specified by the intercept information.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating an exemplary computer network in which a law enforcement agency utilizes a network monitor to monitor packet flows consistent with the principles of the invention.
FIG. 2 is a block diagram illustrating an example embodiment of a network monitor that allows a law enforcement agent to perform monitoring and replication of packet flows consistent with the principles of the invention.
FIG. 3 is a block diagram illustrating an example embodiment of a service card that performs packet flow monitoring and forwarding in accordance with the principles of the invention.
FIGS. 4A-4B are flowcharts illustrating example operation of a service card performing packet flow monitoring and forwarding.
FIG. 5 is a block diagram illustrating an exemplary filter table data structure maintained by the service card.
FIG. 6 is a block diagram illustrating an exemplary filter cache data structure maintained by the service card.
FIG. 7 is a block diagram illustrating an exemplary flow cache data structure maintained by the service card.
FIG. 8 is a block diagram illustrating an exemplary IP tuple array data structure maintained by the service card.
FIG. 9 is a flowchart illustrating example operation of a service card in receiving and storing intercept information in the form of packet flow filters.
FIG. 10 is a flowchart illustrating example operation of the service card in further detail.
FIG. 11 is a schematic diagram illustrating an exemplary embodiment of a network router that provides lawful intercept features and integrates routing functionality.



DETAILED DESCRIPTION
FIG. 1 illustrates an exemplary lawful intercept system 2 in which network monitor 16 of service provider network 6 provides interception (such as “lawful tapping”) of network traffic associated with users 8A-8N (hereinafter, “users 8”). Service provider network 6 may be an edge network or a core service provider network of the Internet, and typically includes routers (not shown) and/or other devices that forward network-based traffic between users 8 and the Internet. Users 8 need not be directly coupled to service provider network 6, and may be part of enterprise networks, access networks, or other networks.
In one embodiment, the routers and/or other devices within service provider network transparently replicate traffic within the network, and forward the replicated traffic to network monitor 16 for monitoring and distributing to law enforcement agents 10A-10N (“LEAs 10”). Alternatively, network monitor 16 may be integrated within one or more of the routers within service provider network 6 so as to provide dual functions: (1) routing of network traffic, and (2) transparent and lawful monitoring of the traffic. Other network devices in which the features may be integrated include gateways, switches, servers, workstations, or other network devices.
In general, LEAs 10 may designate one or more of users 8 for network traffic monitoring and provide network monitor 16 with intercept information 7 that provide criteria for specifying packet flows related to the designated users. LEAs 10 may be associated with one or more law enforcement agencies, and may be located in one or more geographic locations remote from service provider network 6. Typically, a legal court order must be granted prior to LEAs 10 directing network monitor 16 to enable lawful intercept on the designated users 8. Although described for exemplary purposes with respect to a core service provider network 6 within the Internet, the technique may be applied to any type of network, such as a broadband Internet service provider (ISP) network, an enterprise local area network, or any other computer-based network. For example, users 8 may be connected to service provider network 6 via respective broadband links, such as those associated with a cable or digital subscriber line (DSL) service. See United States Patent Application entitled “NETWORK DEVICE HAVING SERVICE CARD FOR DYNAMIC FLOW CAPTURE AND MONITORING OF PACKET FLOWS,” 11/517,232, the entire content of which is incorporated herein by reference.
LEAs 10 interact with one or more lawful intercept (LI) service cards of network monitor 16 to initiate lawful intercept of packet flows associated with one or more of users 8. Once lawful intercept is enabled for a designated one of users 8, the LI service cards of network monitor 16 replicate the data packet streams flowing between the designated user and the Internet that match the intercept information 7 provided by one or more of LEAs 10. The LI service cards forward the copied packets 11 to one or more specified content destinations (e.g., specialized data analyzers—not shown in FIG. 1), which may reside at LEAs 10, service provider network 6, or at remote locations. In one embodiment, in addition to the copied packets, the LI service cards may forward other intercept related information (IRI), e.g., authentication details, access type, (e.g., Dial-Up, DSL, or local area network), username, user IP address, bytes transmitted, bytes received by user, and the like.
The LI service cards of network monitor 16 provide real-time intercept and relaying of specified network-based communications, even under high-volume traffic rates. For example, as described herein, the LI service cards can monitor and replicate targeted network communications for high traffic rates, even core traffic rates of the Internet, including OC-3, OC-12, OC-48, and higher rates. Moreover, the techniques described herein allow LEAs 10 to tap new or existing packet flows within an extremely small period of time after specifying intercept information, e.g., within 50 milliseconds, even under high-volume networks. Further, the techniques can readily be applied in large networks that may have one or more million of concurrent packet flows, and where hundreds of thousands of tap entries may be defined.
LEAs 10 typically provide the intercept information to the LI service cards of network monitor 16 via a remote lawful intercept protocol. In this manner, LEAs 10 may selectively define the packet flows that are intercepted for analysis. Alternatively, LEAs 10 or a system administrator operating under the direction of the LEAs may provide the intercept information directly, e.g., via a keyboard, mouse or other input mechanism, to control interception of packet flows.
The term “packet” is used herein to generally describe a unit of data communicated between resources in conformance with a communication protocol. The principles of the invention may be readily applied to a variety of protocols, such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), the Internet Protocol (IP), Asynchronous Transfer Mode (ATM), Frame Relay, and the like. Accordingly, “packet” is used to encompass any such unit of data, and may be interchanged with the term “cell,” or other similar terms used in such protocols to describe a unit of data communicated between resources within the network.
FIG. 2 is a block diagram illustrating an example embodiment of a network monitor 16 that allows a law enforcement agent to perform monitoring of packet flows consistent with the principles of the invention. In the illustrated embodiment, network monitor 16 includes a physical chassis 23 for housing a control unit 21. Chassis 23 has a number of slots (not shown) for receiving a set of removable cards, including interface cards (IFCs) 22A-22N (collectively, “IFCs 22”) and one or more LI service cards 28A-28M (collectively, “LI service cards 28”). Chassis 23 may receive other service cards, such as accounting service cards, encryption service cards, and tunnel service cards. Each card may be inserted into a corresponding slot of chassis 23 for electrically coupling the card to control unit 21 via a bus, backplane, or other electrical communication mechanism.
IFCs 22 send and receive packet flows via inbound network links 24A-24N (collectively, “inbound network links 24”) and outbound network links 26A-26N (collectively, “outbound network links 26”), respectively. IFCs 22 and service cards 28 are connected with packet forwarding engine 34 by internal links 36. Links 36 may comprise any form of communication path, such as electrical paths within an integrated circuit, data busses, optical links, network connections, wireless connections, or other type of communication path. Although not shown in the embodiment of FIG. 2, LI service cards 28 may also include interface ports for direct coupling to network links.
In one embodiment, network monitor 16 includes a routing engine 38 that maintains routing information that describes the topology of service provider network 6. Routing engine 38 analyzes stored routing information and generates forwarding information stored within packet forwarding engine 34 for forwarding packets received via inbound links 24 to next hops. In order to maintain an accurate representation of the network, network monitor 16 may support a number of protocols for exchanging routing information with other routers. For example, network monitor 16 may support the Border Gateway Protocol (BGP), for exchanging routing information with routers of other autonomous systems. Similarly, network monitor 16 may support the Intermediate System to Intermediate System protocol (IS-IS), which is an interior gateway routing protocol for communicating link-state information within an autonomous system. Other examples of interior routing protocols include the Open Shortest Path First (OSPF), and the Routing Information Protocol (RIP).
Routing engine 38 directs packet-forwarding engine 34 to maintain forwarding information in accordance with the routing information. The forwarding information may, therefore, be thought of as a subset of the information contained within the routing information. In particular, forwarding information associates packet information, referred to as a “key,” with specific forwarding next hops (FNH). A FNH generally refers to a neighboring router physically coupled to a source router along a given route. For example, the FNH for a route may specify a physical interface and media access control (MAC) address for the interface associated with the router. Packet-forwarding engine 34 controls the flow of packets through network monitor 16 in order to integrate routing and forwarding functionality with lawful intercept functionality. In this manner, network monitor 16 may integrate active routing functionality with lawful intercept functionality provided by LI service cards 28. Alternatively, network monitor 16 may be a passive monitor in that packet forwarding engine 34 may direct all inbound traffic received via IFCs 22 to LI service cards 28 without forwarding the traffic to next hops.
In one embodiment, each of packet-forwarding engine 34 and routing engine 38 may comprise one or more dedicated processors, hardware, and the like, and may be communicatively coupled by data communication channel 36. Data communication channel 36 may be a high-speed network connection, bus, shared-memory or other data communication mechanism.
As further described below, LI service cards 28 each include one or more modules that receive packets from packet forwarding engine 34 of control unit 21, associate the packets with packet flows and detect any packet flows matching intercept information provided by LEAs 10. Control unit provides contents of packets received by an IFC 22 to LI service cards 28. In one embodiment, packet forwarding engine 34 performs inline duplication of some or all of the packets to be forwarded, forwards the original packets without disruption, and passes the duplicated packets to one or more LI service cards 28 for packet flow matching. In another embodiment, packet forwarding engine 34 does not duplicate the packets, but passes the original packets to LI service cards 28 to check for matches before forwarding the original packets to their destinations. In one embodiment, LI service cards 28 then inject the matching packets and/or packets containing flow statistics into packet forwarding engine 34 for forwarding to content destinations (CDs) specified by LEAs 10. Alternatively, as a passive monitor, LI service cards 28 drop the matching packet. In either case, packet forwarding engine 34 forwards the original packets in conventional fashion via interface cards 22 in accordance with the forwarding information.
Each LI service card 28 may include one or more microprocessors, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or other components that provide an operating environment for software or firmware. As described, control unit 21 distributes replicated packets to LI service cards 28 for detection of packet flows that match intercept information. In one embodiment, control unit 21 distributes the packets of a common flow to a common LI service card 28.
In one embodiment, control unit 21 applies a hashing function to at least a portion of the header for each packet to ensure that packet flows are distributed across LI service cards 28, and that packets of a packet flow are distributed to a common one of the LI service cards 28. Control unit 21 may apply a hashing function to at least one of a source network address, a destination network address, and a communication protocol for the packet. Control unit 21 may apply the hash function to header information with each packet to generate a hash value, and distribute each packet to one of the LI service cards 28 based on the calculated hash values. Furthermore, portions of the header information may be selected to cause packet fragments associated with a common one of the network packet to be distributed to a common one of the LI service cards 28. For example, layer 4 port information may be ignored, which may not be present for packet fragments.
Multiple LI service cards 28 may be added to easily scale network monitor 16 to support monitoring and lawful intercept for higher bandwidth communication links coupled to IFCs 22. For example, depending upon processing power, two LI service cards 28 may be used to provide real-time monitoring and lawful intercept for a single OC-3 communication link, while four cards and sixteen cards may be used for OC-12 and OC-48 links, respectively. As another example, eight LI service cards 28 may be used to monitor and provide lawful intercept for four OC-3 links. Additional LI service cards 28 may be used for purposes of redundancy to support continuous, uninterrupted packet processing and lawful intercept in the event of card failure.
FIG. 3 is a block diagram illustrating one example embodiment of LI service card 28A of network monitor 16 that performs packet flow monitoring and forwarding in accordance with the principles of the invention. LI service card 28A includes a packet forwarding engine interface 40 (“PFE interface 40”) for communicating with PFE 34 (FIG. 2). PFE interface 40 may be an electrical interface. LI service card 28A receives packets via PFE interface 40, and also forwards packets that match stored intercept information to the appropriate content destinations via PFE interface 40.
LI service card 28A also includes a control unit 42. Control unit 42 provides an operating environment for an LEA interface 44 (e.g., a software communication protocol) that allows LEAs 10 to convey intercept information to LI service card 28A. Intercept information may take the form of a filter, and may comprise criteria for matching one or more flows, such as source interne protocol (IP) address, destination IP address, source port, destination port, and protocol. The intercept information may also include a content destination to which to send a copied packet flow that matches the particular flow criteria.
When LI service card 28A receives a packet via PFE interface 40, flow match detection module 46 determines whether the packet matches any of the filters defined by the stored intercept information, as will be described in further detail below. When the packet matches the intercept information, control unit 42 may cause the packet to be sent to the appropriate content destination via PFE interface 40 and PFE 34, which outputs the packet via one of IFCs 22. In the case where the packet must be sent to more than one content destination, packet replication module 48 may form the appropriate number of copies of the packet having the appropriate destination information within the packet header to effectively direct the packets to the corresponding destinations specified by the intercept information. In embodiments in which network monitor 16 is a passive monitor, LI service card 28A drops the replicated packets after detecting flow matches, and may store flow match information or statistics for concurrent or subsequent analysis.
In support of lawful intercept of high-volume network traffic, control unit 42 includes a number of unique data structures, such as filter cache 50, flow cache 52, filter table 54, and IP tuple array 56. When an LEA 10 provides intercept information in the form of one or more filters, control unit 42 stores the recently received intercept information in filter cache 50. LEA interface 44 may also communicate the received intercept information to any other LI service cards 28 via PFE interface 40, or via a direct connection between the LI service cards 28 without going through PFE 34. As a result, additional LI service cards 28 can be used to intercept packets using the same intercept information, thereby facilitating a scalable system able to support high data rates. After a time period, control unit 42 moves the recently received intercept information from filter cache 50 to filter table 54. Filter table 54 thus stores all of the intercept information, except for the most recent intercept information (e.g., filters) recently received within the specified time period, i.e., active intercept information. Control unit 42 may maintain filter table 54 and filter cache 50 in the form of one or more tables, databases, link lists, radix trees, flat files, or any other data structures.
IP tuple array 56 is an array having a range of source IP addresses as one dimension and a range of destination IP addresses as another dimension. In one embodiment, the array is divided into bins (addressable elements), each bin representing ranges of 1000 by 1000 addresses along the dimensions. In one embodiment, when control unit 42 moves recently received intercept information from filter cache 50 to filter table 54, control unit 42 increments a reference count in the appropriate bin based on the source and destination IP addresses specified the intercept information. In this way, control unit 42 maintains a general representation of where within the IP address space LEAs 10 have defined intercept information. IP tuple array 56 may be used as a mechanism for quickly dropping unmonitored packets to save computational resources, and will be described in further detail below.
When flow match detection module 46 first determines that a newly received or current packet flow matches some of the intercept information, control unit 42 stores the matching portion of the intercept information (e.g., one or more filters matching the packet flow) in a flow cache 52. When processing subsequent packets, flow match detection module 46 may quickly look at the appropriate entry within flow cache 52 for a recent match before accessing filter table 54, which may be quite large (e.g., tens of thousands of filters). In this manner, packets from previously matched flows can be processed more quickly, and a time-consuming lookup of filter table 54 may be avoided.
FIGS. 4A-4B are flowcharts illustrating an overview of example operation of an LI service card 28A of network monitor 16 performing packet flow monitoring and forwarding of lawfully intercepted flows. As shown in FIG. 4A, in this example, LI service card 28A receives intercept information entered by an LEA 10 via LEA interface 44 (FIG. 3) (58). LI service card 28A stores the received intercept information in filter cache 50 (60). LI service card 28A may also share the received intercept information with other LI service cards 28 in network monitor 16, and receive and store intercept information from other LI service cards 28.
As illustrated in FIG. 4B, when LI service card 28A receives a packet via PFE interface 40 (62), LI service card 28A uses flow detection module 46 to determine whether the packet matches any of the stored intercept information by referencing the data structures within control unit 42 (64). The process of determining whether the packet matches intercept information is described below. When the packet does not match any of the intercept information, LI service card 28A drops the packet (66). When the packet matches some of the intercept information, and the intercept information requires that copies of the packet be sent to more than one destination, packet replication module 48 of LI service card 28A replicates the packet (68). In any case, LI service card 28A sends one or more copies of the packet to the one or more destinations specified by the intercept information (70). LI service card 28A may receive and store intercept information, as illustrated in FIG. 4A, concurrently with monitoring and forwarding packets, as illustrated in FIG. 4B.
FIG. 5 is a block diagram illustrating an exemplary filter table 54 maintained by LI service card 28A for performing packet flow monitoring and forwarding. Filter table 32 stores intercept information received by LI service card 28A. In the example shown in FIG. 5, filter table 32 organizes the intercept information in rows of entries, where each entry represents a different filter received from one of LEAs 10. A criteria identifier column 72 includes a unique identifier for each entry.
In this example, a 5-tuple criteria column 74 is used to specify zero or more of a source IP address, destination IP address, source port, destination port, and protocol. An LEA 10 interacts with the LI service card 28 via the LEA interface 44, and specifies the intercept information to obtain copies of any packet flows that match the 5-tuple criteria. A control source column 76 specifies the source of the intercept information, i.e., which LEA may enter with the intercept information. A content destination column 78 specifies the destination to which packets matching the 5-tuple criteria should be sent. The control source and content destinations may be designated by an IP address. In the example of FIG. 5, entry A indicates that copies of packets having a source IP address S1, a destination IP address D1, a source port 80, and a destination port 80, and using the HTTP protocol, should be sent to content destination CS1, which is the same as the control source CS1 that sent the entry.
In some examples, the LEA may specify one or more of the 5-tuple criteria as a wildcard. For example, in entry C, the LEA wants to receive copies of any packets from source IP address S2, regardless of the destination IP address. As another example, in entry B, the LEA wants to receive copies of any packets sent to destination IP address D2, regardless of the source IP address. As a further example, an LEA may specify all of the 5-tuple criteria as wildcards, to monitor any-to-any traffic across the network. Filter table 54 may store all of the intercept information received by LI service card 28A, except for that intercept information received more recently than a given time before the current time. For example, filter table 54 may store all received intercept information except for that intercept information received within the last 30 seconds. In some embodiments in which LI service card 28A does not use a filter cache 50, filter table 54 may store all of the intercept information received by LI service card 28A.
FIG. 6 is a block diagram illustrating an exemplary filter cache 50 maintained by LI service card 28A for performing packet flow monitoring and forwarding. Similar to filter table 32, in this example, filter cache 50 organizes the intercept information in rows of entries, where each entry represents a different filter received from one of LEAs 10. A criteria identifier column 82 includes a unique identifier (e.g., label) for each entry, and a 5-tuple criteria column 84 includes one or more of a source IP address, destination IP address, source port, destination port, and protocol. A control source column 86 and content destination column 88 specify the source of the intercept information and the destination to which packets matching the 5-tuple criteria should be sent, respectively. Add time column 90 contains a timestamp of the time that the entry was added to filter cache 50. Filter cache 50 may store all intercept information received recently, such as all intercept information received by LI service card 28A in the last 30 seconds. Once an entry has been stored in filter cache 50 for more than a specified time (e.g., 30 seconds), control unit 42 flushes the entry by moving the entry from filter cache 50 to filter table 54. Control unit 42 may determine that an entry is more than 30 seconds old by executing a background software task or process that compares the specified add time for each entry to the current time.
Filter cache 50 may have a limited amount of storage space, such as 30 entries. If LI service card 28A receives more than one entry per second, control unit 42 may move entries to filter table 54 sooner than 30 seconds (i.e., the specified caching period in this example) from receipt when filter cache 50 reaches 30 entries.
FIG. 7 is a block diagram illustrating an exemplary flow cache 52 maintained by LI service card 28A that indicates whether packet flows F1-Fn have been recently matched to the flow criteria specified in either filter cache 50 or filter table 54. In one embodiment, flow cache 52 is maintained as a hash table, where the hash value used to index the hash table is computed from packet header data. For example, flow hash column 92 contains flow hash values that operate as indexes for the corresponding row. When LI service card 28A receives a packet, control unit 42 calculates a flow hash based on information contained in a header of the packet. Control unit 42 uses the flow hash as an index into flow cache 52. As explained in further detail below, control unit 42 populates entries of flow cache 50 when flow match detection module 46 accesses filter cache 50 or filter table 54 to determine whether a received packet matches the criteria of one or more intercept information entries. Control unit 42 updates an entry of flow cache 52 for every received packet to record, either positively or in the negative, whether or not the packet matches any intercept information.
In this example, matching criteria column 94 contains the criteria identifier for the entry or entries of filter cache 50 or filter table 54 that flow match detection module 46 has recently determined match the packet of a given flow F, along with a flow identifier. For example, the entry of flow cache 52 corresponding to hash value H172 shows that the packets of flow F2 match entry A of filter table 54. In this way, flow match detection module 46 can check flow cache 52 first to see whether flow cache 52 has a matching entry for the packet. If so, flow match detection module 46 can go directly to the entry of filter table 54 listed in matching criteria column 94, instead of having to traverse filter table 54 in its entirety. As flow cache 52 is implemented as a hash table or other suitably fast access data structure, fast determination of any matching filters can be identified without requiring potentially time-consuming traversal of filter table 54 for each packets. As a result, high data rates can be achieved.
Expiration time column 96 (EXP. TIME 96) contains an expiration time. The expiration time indicates the time at which the corresponding entry of flow cache 52 is to be flushed, provided no additional packets for the flow are received prior to the expiration time. Timer duration column 97 specifies the amount of time, i.e., the length of time to be used for expiration and flushing of the entry by control unit 42. Control unit 42 uses the expiration time and the timer duration to ensure both that flow cache 52 does not grow too big, and to prevent flow cache 52 from containing information that is out-of-date with respect to filter table 54. First, whenever a packet is received for a flow listed in matching criteria column 94 of flow cache 52, control unit 42 resets the corresponding expiration time according to the time duration. This ensures that flows that are still active within the expiration time are not flushed. For example, if a packet were received at 23:40:03 for the flow listed in H172, control unit 42 would reset the expiration time to 28:40:03, i.e., five minutes from the current time. If the time 28:40:03 were reached without interface card 28A receiving another packet for H172, control unit 42 would flush entry H172 by clearing the matching entries.
Second, whenever control unit 42 adds an entry to filter cache 50 that is matched by a flow listed in flow cache 50, control unit 42 changes the timer duration in all entries of flow cache 52 from a first timer duration to a second timer duration, e.g., from five minutes to thirty seconds. The second timer duration may correspond to the maximum amount of time that an intercept information entry may be cached in filter cache 50 before being moved to filter table 54. When the corresponding entry in filter cache 50 has been moved from filter cache 50 to filter table 54, all entries in flow cache 52 will have been flushed, and when a subsequent packet for a flow is received, flow match detection module 46 will not get out-of-date information from flow cache 52. Instead, flow match detection module 46 will see that there is no entry in flow cache 52 that matches the flow, and will move on to check filter table 54, where the intercept information entry has been moved.
A packet may match more than one entry of filter table 54, as illustrated by the entry of flow cache 52 corresponding to hash value H105. In this entry of flow cache 52, F1 matches both entries A and B of filter table 54. In some cases, more than one flow may hash to the same hash value. For example, the entry of flow cache 52 corresponding to hash value H105 contains two different matching entries. In this case, both flow F1 and flow F4 hash to the same value H105, and match different entries of filter table 54. Further, an entry in flow cache 52 may be a null entry; that is, the entry may reflect that a flow has recently been hashed to that entry, and the flow does not match any of the entries in filter table 54. An example of this is the entry of flow cache 52 corresponding to hash value H30.
FIG. 8 is a block diagram illustrating an exemplary IP tuple array 56 maintained by LI service card 28A for performing packet flow monitoring and forwarding. IP tuple array 56 is an array of reference counts having a range of source IP addresses as one dimension and a range of destination IP addresses as another dimension. In one embodiment, the array is divided into bins (entries) that are indexed by ranges of 1000 by 1000 addresses along each dimension. Control unit 42 increments a reference count (i.e., index) associated with the appropriate bin of IP tuple array 56 each time control unit 42 moves an intercept information entry from filter cache 50 to filter table 54. For example, the reference count associated with bin 98 has been incremented ten times, while the reference count associated with bin 100 has been incremented once. In the example of FIG. 8, the bins not called out have reference counts of zero. Thus, any given bin having a non-zero reference count indicates that at least one entry exists in filter table 54 having criteria that specify source and destination addresses within the addresses ranges associated with the bin. In this way, control unit 42 maintains a general representation of where in the IP address space LEAs 10 have specified intercept information.
Flow match detection module 46 may consult IP tuple array 56 before looking up a packet in filter table 54. IP tuple array 56 may be somewhat sparsely populated. In some embodiments, the dimensions of IP tuple array 56 may have different levels of granularity. A large number of packets received by LI service card 28A will likely not match any of the stored intercept information. Flow match detection module 46 may use IP tuple array 56 to drop those packets for which LI service card 28A does not have any intercept information, without needing to traverse the entire filter table 54. As a result, the use of IP tuple array 56 may reduce the processing time of LI service card 28A.
When an entry being moved to filter table 54 contains a wildcard, such as entry C of filter table 54 (FIG. 5), control unit 42 may increment multiple bins of IP tuple array 56 for a single entry of filter table 54. In the example of entry C of filter table 54, each of the bins corresponding to source IP address S2 would be incremented, because a packet having source IP address S2 and any destination address would match entry C.
FIG. 9 is a flowchart illustrating in more detail exemplary operation of LI service card 28A in receiving and storing intercept information from LEAs 10. LI service card 28A receives intercept information via LEA interface 44 (FIG. 3) (102). LI service card 28A first adds an entry for the intercept information to filter cache 50 (104). In addition, since an entry is present in filter cache 50, control unit 42 of LI service card 28A changes the time duration from a first time duration to a time duration for all entries in flow cache 52 (106). For example, in one embodiment control unit 42 reduces the time duration from five minutes to thirty seconds, where thirty seconds is specified as the time duration that an entry may be cached within filter cache 50. When control unit 42 determines that the expiration time has been reached for an entry of filter cache 50 by comparing the expiration time to the current time (108), control unit 42 increments IP tuple array 56 (110) and moves the entry from filter cache 50 to filter table 54 (112).
FIG. 10 is a flowchart illustrating in more detail exemplary operation of LI service card 28A performing packet flow monitoring and forwarding consistent with the principles of the invention. LI service card 28A receives a packet via PFE interface 40 (FIG. 3) (120). In some embodiments, flow match detection module 46 of control unit 42 first determines whether a set of early drop conditions is met (122). Example early drop conditions are that there are currently no entries in filter cache 50, and that the hash bucket corresponding to the packet includes a single matching entry that indicates no match (a “null entry”). If flow match detection module 46 determines that both conditions are met, control unit 42 drops the packet (124). If any of the conditions are not met, for example, filter cache 50 currently contains entries; there are multiple entries for the hash value in flow cache 52; or there is no information at all in flow cache 52 for this hash value, then flow match detection module 46 proceeds.
Where early drop conditions are not met, flow match detection module 46 determines whether the packet matches any entry in filter cache 50 (126). Flow match detection module 46 compares the packet to the 5-tuple criteria of each entry in filter cache 50. If flow match detection module 46 detects one or more matches, control unit 42 updates flow cache 52 by populating the matching criteria column 94 (FIG. 7) of the entry for the flow hash value (128). Control unit 42 forwards copies of the packet to the destination(s) specified by the matching entry in filter cache 50, with appropriate consultation of forwarding information to determine next hops (130).
Where no match is found in filter cache 50, flow match detection module 46 determines whether an entry for the packet exists in flow cache 52 (132). To do this, flow match detection module 46 calculates the hash value for the packet based on information within the header of the packet, and accesses the bin of flow cache 50 that corresponds to the calculated hash value. If a matching entry exists in flow cache 50 (YES branch of 134), flow match detection module 46 accesses the one or more entries of filter table 54 indicated by the matching entry of flow cache 50, and forwards the packet according to the intercept information in filter table 54 (136). If there are multiple matches to the packet and the intercept information indicates packets are to be sent to different content destinations, packet replication module 48 replicates the packet, and control unit 42 forwards one of the replicated packets to each of the appropriate destinations. Where an entry exists in flow cache 52 but the entry indicates there is no match, i.e., a null entry (NO branch of 134), control unit 42 drops the packet (138).
Where no entry exists in flow cache 52 (i.e., a cache miss), flow match detection module 46 checks the packet against IP tuple array 56 (140). In particular, flow match detection module 46 accesses the bin (element) corresponding to the source and destination IP addresses of the packet. If the index (reference count) of the bin is zero, this indicates that LI service card 28A does not have intercept information for the ranges of IP addresses that cover the particular IP addresses of the packet. Control unit 42 updates the entry of flow cache 52 to reflect that no match was found for this flow (142), and drops the packet (138), thereby avoiding traversing filter table 54.
Where the index of the bin of IP tuple array 56 is non-zero, flow match detection module 46 proceeds to determine whether the packet matches any entry in filter table 54 (144). Flow match detection module 46 checks the packet against each entry in filter table 54. If no match is found, control unit 42 updates the entry of flow cache 52 to reflect that no match was found for this flow (142), and drops the packet (138). If the packet matches one or more entries of filter table 54, control unit 42 updates the entry of flow cache 52 to reflect that the flow matches the entries (146). Control unit 42 then forwards the packet according to the intercept information in filter table 54 (136). If there are multiple matches to the packet and the intercept information indicates packets are to be sent to different content destinations, packet replication module 48 replicates the packet, and control unit 42 forwards the packets to the appropriate destinations. In addition to the copied packets, the LI service cards may forward intercept related information (IRI), e.g., authentication details, access type, (e.g., Dial-Up, DSL, or local area network), username, user IP address, bytes transmitted, bytes received by user, and the like. These techniques allow network monitor 16 to transmit copies of the matching packet flows within an extremely small period of time after specifying intercept information, e.g., within 50 milliseconds.
FIG. 11 is a schematic diagram illustrating an exemplary embodiment of a network router 150 that provides lawful intercept features and, in this example, integrates routing functionality. In the illustrated embodiment, network router 150 includes a chassis 152 for housing control unit 151 having a routing engine and a packet forwarding engine (not shown). In the illustrated example, chassis 152 has nine slots for receiving a set of cards. In particular, chassis 152 receives four interface cards (IFCs) 154, three LI service cards 156, an encryption service card 158, and a tunnel service card 160. Each card may be inserted into a corresponding slot of chassis 152 for electrically coupling the card to control unit 151 via a bus, backplane, or other electrical communication mechanism. Interface cards 154 include ports for coupling to communication links.
Various embodiments of the invention have been described. Although described with respect to lawful intercept, the technique can readily be applied to other environments where multiple control sources need to independently monitor and intercept particular packet flows. Examples of other such environments include system administration, accounting, traffic analysis, network attack detection, intrusion detection and the like. These and other embodiments are within the scope of the following claims.

## Claims

1. A network device comprising:
a lawful intercept (LI) service card executing a communication protocol to receive, from one or more law enforcement agents (LEAs), intercept information specifying at least one destination and criteria for matching one or more packet flows;
a network interface card to receive a packet from a network;
a control unit to provide contents of the packet from the interface card to the LI service card, wherein the LI service card executes a flow match detection module that determines whether the contents of the packet match the criteria of the intercept information and, when the contents of the packet match the criteria of the intercept information, forwards the packet to the destination specified by the intercept information;
a filter cache that caches intercept information recently received from the LEAs;
a filter table that stores all of the intercept information received from the LEAs except the intercept information cached in the filter cache; and
an array of reference counts addressable by a range of source IP addresses as one dimension of the array and a range of destination IP addresses as another dimension of the array, wherein each reference count indicates a number of filters specified by the intercept information capable of matching at least one address within the address ranges associated with the reference count.

2. The network device of claim 1, wherein the network device comprises a packet forwarding engine that replicates the received packet, and wherein the control unit provides the replicated packet to the LI service card.

3. The network device of claim 1, wherein the LI service card matches criteria for intercept information and forwards matching packets no later than 50 milliseconds from when the intercept information is received from the LEAs.

4. The network device of claim 1, wherein the filter cache includes a plurality of entries, and each entry specifies a filter defining: (i) at least one criteria of: a source IP address, a destination IP address, a source port, a destination port, or a protocol, (ii) a source associated with the LEA that requested the filter, and (iii) the destination to which packets matching the criteria should be sent.

5. The network device of claim 1, wherein the flow match detection module flushes the filter cache and moves the recently received intercept information from the filter cache to the filter table.

6. The network device of claim 1, wherein when the LI service card moves intercept information from the filter cache to the filter table, the LI service card increments the reference count in the appropriate array element of the array based on a source IP address and a destination IP address specified by the intercept information moved from the filter cache to the filter table.

7. The network device of claim 1, wherein the LI service card drops the packet when: (1) there is no matching criteria within the filter cache, and (2) the corresponding reference count within the array indicates that no filter has been specified for a range of source IP addresses and a range of destination IP addresses that cover the source and destination IP addresses of the packet.

8. The network device of claim 1, further comprising a flow cache within the LI service card, wherein each entry within the flow cache indicates whether packets recently received from the control unit by the LI service card matches any of the criteria specified within the intercept information.

9. The network device of claim 8, wherein each of the entries in the flow cache is addressable based on a hash of data within the packets.

10. The network device of claim 8, wherein when the LI service card determines that the received packet matches some of the intercept information, the LI service card selects one of the entries within the flow cache based on a hash of the received packet, and stores in the selected entry of the flow cache the data identifying the matching criteria and destination specified by the intercept information.

11. The network device of claim 1, further comprising:
a filter cache within the LI service card that caches intercept information recently received from the LEAs; and
a flow cache within the LI service card, wherein each entry within the flow cache indicates whether packets recently received from the control unit by the LI service card match any of the criteria specified within the intercept information,
wherein when the LI service card adds an entry to filter cache, the LI service card automatically changes an expiration time associated with all entries of the flow cache from a first time duration to a second time duration.

12. The network device of claim 11, wherein the LI service card sets the second time duration to a maximum amount of time that an intercept information filter from the LEAs may be cached in the filter cache.

13. The network device of claim 1, further comprising:
a filter cache within the LI service card that caches intercept information recently received from the LEAs; and
a flow cache within the LI service card, wherein each entry within the flow cache indicates whether packets recently received from the control unit by the LI service card matches any of the criteria specified within the intercept information,
wherein the LI service card drops the packet without further processing when: (i) there are currently no entries in the filter cache, and (ii) the flow cache indicates that no recently received packets having a same hash as the packet have matched any of the criteria specified within the intercept information.

14. The network device of claim 1, wherein the intercept information includes one or more filters specifying the criteria for matching one or more packet flows to be intercepted, and wherein the criteria includes at least one of a source network address, a destination network address, a protocol, a source port number, a destination port number, and an ingress port number for the network interface card of the network device.

15. The network device of claim 14, wherein one or more of the criteria is specified as a wildcard.

16. The network device of claim 1, wherein the LI service card automatically communicates the received intercept information to other LI service cards within the network device.

17. The network device of claim 1, further comprising a chassis having a plurality of slots to receive and couple the network interface cards and the LI service card to the control unit.

18. The network device of claim 1, wherein the control unit comprises a routing engine to maintain routing information representing a topology of the network, and the control unit receives one or more replicas of the network packet from the LI service card and forwards the replicas of the network packet to output ports of the network interface card in accordance with the routing information.

19. The network device of claim 18, wherein the routing engine generates forwarding information in accordance with the routing information, and wherein the control unit comprises a forwarding engine to forward the network packets in accordance with the forwarding information.

20. The network device of claim 1, wherein the network device includes at least four LI service cards that collectively match criteria for intercept information and forward matching packets at OC-48 rates and higher.

21. The network device of claim 1, wherein the network device includes a plurality of LI service cards that collectively match criteria for intercept information and forward matching packets at OC-12 rates and higher.

22. The network device of claim 1, wherein the LI service card matches criteria for intercept information and forwards any matching packets for at least one million of concurrent packet flows.

23. A lawful intercept (LI) service card comprising:
an electrical interface for insertion within a slot of a network device;
an law enforcement agents (LEAs) interface executing within the LI service card to receive intercept information specifying one or more flow criteria;
a flow match detection module executing within the LI service card to receive a packet from the network device via the electrical interface, wherein the packet was received at the network device via a separate interface card prior to the flow match detection module receiving the packet via the electrical interface, wherein the flow match detection module determines whether the packet matches the flow criteria of the intercept information and, when the packet matches the flow criteria of the intercept information, forwards the packet to a destination associated with the LEAs;
a filter cache that caches intercept information received from the LEAs within a previous time period;
a filter table that stores all intercept information received from the LEAs except for the intercept information cached in the filter cache;
an array of reference counts addressable by a range of source IP addresses as one dimension and a range of destination IP addresses as another dimension, wherein each reference count indicates a number of filters specified by the LEAs for the addresses ranges associated with the reference count; and
a flow cache, wherein each entry in the flow cache indicates whether a recently received packet flow matches any of the criteria specified by the LEAs.

24. A method comprising:
receiving, with a lawful intercept (LI) service card of a network device, intercept information from one or more law enforcement agent (LEAs), wherein the intercept information specifies at least one destination and at least one criteria for matching one or more packet flows;
caching the intercept information recently received from the LEAs within a filter cache;
moving the intercept information from the filter cache to a filter table upon expiration of a timer;
flushing the filter cache by moving at least a portion of the recently received intercept information from the filter cache to a filter table that stores all of the intercept information received from the LEAs, except for any intercept information currently cached in the filter cache;
maintaining an array of reference counts addressable by a range of source IP addresses as one dimension of the array and a range of destination IP addresses as another dimension of the array, wherein each reference count indicates a number of filters specified by the intercept information capable of matching the addresses ranges associated with the reference count;
receiving a packet from a network via an interface card of a network device;
providing contents of the packet from the interface card to the LI service card;
determining, with the LI service card, whether contents of the packet match the flow criteria of the intercept information; and
when the contents of the packet match the flow criteria of the intercept information, outputting the contents of the packet from the LI service card to the destination specified by the intercept information.

25. The method of claim 24, further comprising, when the contents of the packet match the flow criteria and the intercept information specifies a plurality of destinations, replicating the packet and outputting one of the replicated packets to each of the plurality of destinations.

26. The method of claim 24, further comprising, when flushing the filter cache, incrementing the reference count in the appropriate array element of the array based on a source IP address and a destination IP address specified by the intercept information moved from the filter cache to the filter table.

27. The method of claim 24, further comprising dropping the packet when: (1) the filter cache is empty, and (2) the corresponding reference count within the array indicates that no filter has been specified for a range of source IP addresses and a range of destination IP addresses that cover the source and destination IP addresses of the packet.

28. The method of claim 24, further comprising maintaining a flow cache that identifies packet flows that have recently been matched to one or more of the criteria specified within the intercept information.

29. The method of claim 28, further comprising:
performing a hash on the received packet; and
accessing an entry within the flow cache based on a result of the hash to determine whether a packet flow associated with the packet has been recently matched to one or more of the criteria.

30. The method of claim 24, further comprising:
maintaining a flow cache that identifies packet flows that have been matched to one or more of the criteria specified of the intercept information within an expiration time;
caching, within a filter cache, intercept information received from the LEAs within a filter cache; and
when receiving new intercept information from the LEAs and adding an entry to the filter cache, automatically changing the expiration time associated with all entries of the flow cache from a first time duration to a second time duration.

31. The method of claim 30, further comprising setting the second time duration to a maximum amount of time that an intercept information filter from the LEAs may be cached in the filter cache.

32. The method of claim 24, further comprising forwarding the packets from the LI service cards to a control unit of the network device for routing in accordance with routing information for the network.

33. The method of claim 24, further comprising inserting the network interface cards and the LI service cards into the network device via slots within a chassis of the network device to electrically couple the network interface cards and the LI service cards to a control unit of the network device.

34. A method comprising:
receiving, with a lawful intercept (LI) service card of a network device, intercept information from one or more law enforcement agent (LEAs), wherein the intercept information specifies at least one destination and at least one criteria for matching one or more packet flows;
storing the intercept information received from the LEAs in a filter table;
caching intercept information recently received from the LEAs within a filter cache;
maintaining a flow cache that identifies packet flows that have recently been matched to one or more of the criteria specified within the intercept information;
maintaining an array of reference counts addressable by a range of source IP addresses as one dimension of the array and a range of destination IP addresses as another dimension of the array, wherein each reference count indicates a number of filters specified by the intercept information capable of matching the addresses ranges associated with the reference count;
receiving a packet from a network via an interface card of a network device;
providing contents of the packet from the interface card to the LI service card;
determining, with the LI service card, whether contents of the packet match the flow criteria of the intercept information; and
when the contents of the packet match the flow criteria of the intercept information, outputting the contents of the packet from the LI service card to the destination specified by the intercept information,
wherein determining whether the packets matches the flow criteria of the intercept information comprises:
(i) upon receiving the packet, accessing the filter cache to determine whether the packet matches any recently received intercept information and, if so, forwarding the packet to one or more destinations,
(ii) upon finding no match within the filter cache, accessing the flow cache based on a hash of the packet to determine whether a packet flow associated with the packet has been recently matched to one or more of the criteria and, if so, forwarding the packet to one or more destinations,
(iii) upon finding no match within the flow cache, accessing the array to determine whether at least one filter specified by the intercept information is capable of matching the addresses of the packet and, if not, dropping the packet, and
(iv) upon finding that the array indicates that at least one filter specified by the intercept information is capable of matching the addresses of the packet, traversing the filter table to identify any filters matched by the packet and, upon identifying one or more filters, forwarding the packet to one or more destinations.