# Patent

## Title
Method for testing stateful network communications devices

## Abstract

There is disclosed a method for testing a stateful network communications device. A plurality of stateful and simulated stateless connections are established with the device under test. Packets are sent to the device under test, and responses are received from the device enter test, over the stateless and stateful connections. Measurements are obtained for at least one of the stateless and stateful connections.

## Background
RELATED APPLICATION INFORMATION
This patent is a continuation of U.S. application Ser. No. 09/968,432, filed Oct. 1, 2001, entitled “METHODS AND SYSTEMS FOR TESTING STATEFUL NETWORK COMMUNICATIONS DEVICES”.


NOTICE OF COPYRIGHTS AND TRADE DRESS
A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become trade dress of the owner. The copyright and trade dress owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright and trade dress rights whatsoever.
BACKGROUND
1. Field
The present invention relates to methods and systems for testing network communications devices. More particularly, the present invention relates to methods and systems for testing stateful network communications devices.
2. Description of the Related Art
Testing high capacity, IP-based intelligent networks requires the origination of Internet-scale volumes of simulated user traffic in laboratory environments. The current generation of high-speed network performance testing equipment is based on either:

    
    
        Proprietary hardware-based “packet blasters” that use pre-configuring quasi-static packets at or near “wirespeed;” or
        TCP socket-based software that runs on large numbers of general purpose (or slightly modified) computing platforms.
    
    


As the density, speed and intelligent traffic management capabilities of network devices increase, traditional high-volume traffic generation solutions are less able to simulate real-world scenarios.
FIG. 1 illustrates the components of the headers in a typical HTTP request/response packet. Traditional network routing and switching devices are stateless in that these devices make decisions based on information that is contained within these headers without maintaining any information about previous packets. They do not maintain any type of connection to the client or server at either end of the TCP transaction.
In order to test a stateless device, simulated traffic only needs to look like “real” traffic on a packet-by-packet basis. There does not need to be a complex relationship between the packets, so the transmitting device does not need to maintain any state or have any dynamic behaviors. For this reason, the current generation of high performance traffic generators do not require a full TCP/IP stack for performance testing. Specialized hardware is used to generate wirespeed packets that are varied algorithmically by overlaying variable length incrementing or random patterns over a “base packet” without any consideration of received packets. These conventional stateless test devices are commonly referred to as packet blasters.
True TCP sessions contain a feedback mechanism. For example, a TCP receiver sends acknowledgement packets to a TCP sender that advertise a window size to the TCP sender that inform the TCP sender the size of the receiver's receive buffer. The sender uses the advertised window size to control the flow of packets sent to the receiver. This mechanism causes the flow of incoming traffic to vary as a function of receiver performance. For instance, as a TCP receiver becomes overloaded, the rate of removing and processing packets from its TCP receive buffer decreases. As a result, the window size advertised to the sender decreases, and the TCP sender slows the flow of packets sent to the receiver. In addition, the mechanism can generate redundant data. For example, if a TCP receiver receives an out-of-sequence packet, the receiver will send a duplicate acknowledgement to the sender indicating that an out of sequence packet was received. Because this feedback mechanism exists on every TCP connection, overall TCP session throughput becomes the dominant performance metric.
Unlike traditional switches and routers, server load-balancing (SLB) devices may maintain state. In the most basic implementations, this takes the form of “persistent sessions” where all packets from a specific user (source IP address) are routed to the same server (destination IP address). In order to accomplish this, the SLB may maintain a table of established client/server connections and look up the server to which a packet should be routed based on the client address.
The next generation of SLB devices is much more sophisticated. They may make routing decisions based on a combination of data from the IP, TCP and HTTP header (URL, Cookie) and may even actively participate in a client/server session by proxying and aggregating multiple client connections into a pool of pre-existing server connections. Since the SLB may have a full TCP/IP stack, it becomes much more difficult to test the device with stateless, algorithmically generated traffic. The performance of the SLB is sensitive to many more characteristics of the TCP session. Table 1 shown below summarizes the information in a received packet processed by various IP-based communications devices.







TABLE 1







Routing Device Header Awareness











Header Field
Switch
Router
Traditional SLB
Nextgen SLB





MAC DA/SA
X
X
X
X


Ethernet FCS
X
X
X
X


IP DA/SA

X
X
X


IP Checksum

X
X
X


TCP src/dst port



X


TCP Sequence #



X


TCP Checksum



X


HTTP URL



X


HTTP Cookie



X









In Table 1, it can be seen that switches and routers only process Ethernet and IP headers, respectively. Traditional server load balancers process the IP source and destination address fields and TCP source and destination port fields. Next generation server load balancers process every header from the Ethernet header through application-level headers. As a result, these next generation devices cannot be tested using traditional stateless packet blasters.
Today's load balancing switches generally handle tens of thousands of session establishments per second with fewer than 100,000 concurrent sessions established. Moore's Law is adhered to not only in general purpose computing platforms but in network devices as well: the new generation of load balancers will handle hundreds of thousands of sessions per second with 1,000,000 or more concurrent sessions established.
While stateless hardware-based solutions cost a fraction as much as fully stateful software-based solutions for high packet rates, stateless solutions do not provide realistic enough traffic to accurately measure the performance of stateful network communications devices, such as new generation SLBs. In fact, SLB devices that proxy connections with nearly a full TCP stack will drop simulated connections attempted by such a device. At the other extreme, software-based full stack implementations are prohibitively expensive to acquire and difficult to maintain and operate for high rates and/or volumes of connections. For example, software-based full TCP stack implementations require multiple may require multiple machines with multiple processors and network interfaces to achieve the number of TCP sessions required to test a stateful network communications device, such as a server load balancer. Accordingly, there exists a long-felt need for economical methods and systems for testing stateful network communications devices capable of simulating a realistic mix of network traffic.
SUMMARY OF THE INVENTION
The present invention includes methods and systems for testing stateful network communications devices. Stateful network communications devices that may be tested by embodiments of the present invention include any type of device that maintains state, such stateful servers, server load balancers, firewalls, secure sockets layer (SSL) accelerators, etc. The methods and systems according to the present invention are capable of simulating a realistic mix of traffic without requiring all of the sessions or connections used in a test to be stateful. According to one exemplary method, a number of simulated stateless connections are established with a device under test. Stateful TCP/IP connections are also established with the device under test. Packets are sent to the device under test over the stateful and stateless connections. Performance and behavior measurements are taken on the stateful connections. These performance measurements are used to modify the behavior of the stateless connections in order to simulate a realistic mix of network traffic. Because the present invention does not require all of the connections to be stateful, the amount of hardware required to test a stateful network communications device is reduced.
Accordingly, it is an object of the present invention to provide improved methods and systems for testing a stateful network communications device.
It is another object of the invention to provide methods and systems for testing a stateful network communications device that use both stateful and simulated stateless connections.
It is yet another object of the present invention to provide a system for testing a stateful network communications device using a reduced amount of hardware over conventional systems.
Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.



DESCRIPTION OF THE DRAWINGS
A description of preferred embodiments of the invention will now proceed with reference to the accompanying drawings.
FIG. 1 is a block diagram of a packet structure for HTTP.
FIG. 2 is a block diagram of a system for testing a stateful network communications device according to an embodiment of the present invention.
FIG. 3 is a block diagram of exemplary hardware that may be associated with a system for testing a stateful network communications device according to an embodiment of the present invention.
FIG. 4 is a flow chart illustrating exemplary steps for testing a stateful network communications device according to an embodiment of the present invention.
FIG. 5A is a flow chart illustrating exemplary operations performed by a programmable stateless packet processor according to an embodiment of the present invention.
FIG. 5B is a block diagram illustrating exemplary data structures that may be used by a programmable stateless packet processor in responding to incoming packets according to an embodiment of the present invention.
FIG. 6 is a message flow diagram illustrating exemplary messages sent between a test device and a device under test according to an embodiment of the present invention.
FIG. 7 is a screen shot of a configuration screen of a system for testing a stateful network communications device according to an embodiment of the present invention.
FIG. 8 is a screen shot illustrating exemplary test results collected by a system for testing a stateful network communications device according to an embodiment of the present invention.



DETAILED DESCRIPTION
FIG. 2 is a functional block diagram illustrating exemplary components of a system for testing a stateful network communications device according to an embodiment of the present invention. In FIG. 2, test system 100 includes a first test device 102 and a second test device 104 for testing a device under test 106. In the illustrated example, device under test 106 is a server load balancer. Although the example illustrated in FIG. 2 includes two test devices, the present invention is not limited to using two test devices to test a server load balancer. For example, in an alternative test scenario, a single test device could be used to test a server load balancer or other device. However, using two test devices to test a server load balancer is preferred because one test device can function as a client and the other test device can function as multiple servers. In yet another alternative test scenario, one or more test devices 102 may be configured as clients and used to test the TCP functionality of a server, such as a web server.
In FIG. 2, test devices 102 and 104 each include TCP/IP stacks 108 for implementing full TCP/IP communications capabilities. By “full TCP/IP communications capabilities,” it is meant that TCP/IP stacks 108 implement the full TCP protocol, including timeouts, retransmissions, flow control, etc. The TCP protocol that may be implemented by TCP/IP stacks 108 is described in IETF RFCs 675, 761, and 793, the disclosures of which are incorporated herein by reference in their entirety. The IP protocol that may be implemented by TCP/IP stacks 108 is described in IETF RFCs 760 and 791, the disclosures of which are incorporated herein by reference in their entirety. According to the present invention, data collected on full TCP/IP sessions established by TCP/IP stacks 108 will be used to modify test behavior on the simulated stateless TCP/IP connections, as will be discussed in more detail below.
The operation of TCP/IP stacks 108 can be contrasted with that of programmable stateless packet processors 110. Programmable stateless packet processors 110 simulate TCP/IP communications in a stateless manner. By “stateless,” it is meant that programmable stateless packet processors 110 make response decisions based only on information contained in an inbound packet. Programmable stateless packet processors 110 preferably do not maintain any state about a connection from one packet to the next. For example, when programmable stateless processors 110 receive a SYN packet, processors 110 formulate and send a SYN plus ACK. Programmable stateless packet processors 110 preferably do not implement of the stateful procedures implemented by TCP/IP stacks 108. For example, programmable stateless packet processors 110 may not implement flow control or retransmissions, both of which require complex code and processing resources. Because programmable stateless packet processors 110 make decisions based on information in inbound packets, programmable stateless packet processors 110 are not required to maintain connection tables of open TCP sessions. The lack of connection tables greatly reduces the processing and memory required for each simulated connection over that of a full TCP/IP session or connection. As a result, TCP/IP test devices 102 and 104 can simulate more TCP/IP sessions with a reduced amount of hardware over conventional full-stack test devices while still causing the DUT to add or reference information in its own state table.
The behavior of programmable stateless packet processors 110 is preferably programmable or controllable by TCP amplification (AMP) controllers 112. TCP AMP controllers 112 receive performance metrics regarding stateful TCP connections maintained by TCP/IP stacks 108 and use this information to modify the behavior of the simulated stateless TCP connections. Performance metrics may be obtained directly from TCP/IP stacks 108 or from an external measurement device 114, such as a packet sniffer. Exemplary performance measurements that may be used include retransmission rate, fragmentation, packet sizes, drop/reset rates, and other information that requires stateful TCP session handling. These metrics can be used to change the corresponding behavior of the stateless TCP connections implemented by programmable stateless packet processors 110 to more closely simulate a realistic mix of traffic. For instance, if measurement device 114 detects that a certain percentage of TCP/IP segments are being retransmitted, TCP AMP controller 112 on test device 102 may instruct programmable stateless packet processor 110 to retransmit the same percentage of TCP segments on the stateless connections. Thus, by using data collected on the stateful connections to modify test conditions on the stateless connections, test devices 102 and 104 closely simulate live network connections.
Test devices 102 and 104 may also include filters 116 for filtering data received on stateless and stateful TCP connections. For example, filters 116 may contain tables that associate IP addresses with stateless and stateful connections. When a packet is received over one of the connections, filters 116 determine whether to send the packets to TCP/IP stack 108 or programmable stateless packet processor 110 based on the connection tables.
Test devices 102 and 104 preferably also include TCP applications 118 and 120. In the illustrated example, TCP application 118 may be a client application, such as an HTTP client application. TCP application 120 may be a TCP server, such as an HTTP server. The present invention is not limited to using HTTP to test a device under test. Any application capable of using the underlying services of TCP to send or receive data is within the scope of the invention. For example, other applications that may be used include FTP, telnet, or other stateful application.
In the example illustrated in FIG. 2, components 108, 112, and 118 are illustrated as being implemented in software, while components 110 and 116 are illustrated as being implemented in hardware. However, the present invention is not limited to such an implementation. Any of the components illustrated in FIG. 2 may be implemented in hardware, software, or a combination of hardware and software.
FIG. 3 is a block diagram of exemplary hardware for system for testing a stateful network communications device according to an embodiment of the present invention. In FIG. 3, test device 102 includes a processor 200 and processor memory 202. Components 200 and 202 may be used to run TCP/IP stacks 108, and TCP AMP controllers 112.
Transmit field programmable gate array (TX FPGA) 204 and buffer memory 206 may implement programmable stateless packet processors 110 illustrated in FIG. 2. Using an FPGA to implement programmable stateless packet processors 110 is preferred because an FPGA is capable of performing limited processing on data at much higher rates than a general-purpose processor. In addition, the behavior of an FPGA can be modified at runtime without flow interruption by an application running on a local processor or an application running on another processor via the system interface. For example, if TX FPGA 204 implements the programmable stateless packet processor 110, and TCP AMP controller is implemented on processor 200, output from TCP AMP controller 112 executing on processor 200 may be used to alter the behavior of programmable stateless packet processor 110 executing on TX FPGA 204.
In the illustrated embodiment, test device 102 includes an RX FPGA 208 and buffer memory 210. Components 208 and 210 preferably implement packet filters 116 illustrated in FIG. 2. In particular, RX FPGA 208 receives packets from the physical network interface and forwarding the packets to either programmable stateless packet processor 110 or TCP/IP stack 108. Like TX FPGA 204, RX FPGA 208 is capable of performing limited processing on data at much higher rates than a general-purpose processor. In addition, the behavior of RX FPGA 208 can be modified on the fly by an application running on a local processor or an application running on another computer via the system interface.
Physical layer chip 212 provides the physical interface for transmitting and receiving packets. The type of interface implemented by component 212 may be an electrical interface or an optical interface. For example, component 212 may implement Ethernet over a 100 Base T copper media or IP using Packet Over SONET over optical media. In the illustrated example, processor 200, TX FPGA 204, and RX FPGA 208 are connected via address lines 216, data lines 218, and a system bus 220. System bus 220 allows a host controller or client application to manage multiple ports in a coordinated fashion. For example, in an actual implementation, multiple adapter cards, each containing the multiple sets of the components in FIG. 3, may be used where each adapter has one or more physical network interfaces. The adapter cards may be plugged into a host system (chassis), which may include a general-purpose computer. TCP application 118 or 120 may execute on the embedded processor 200 or on the host system processor. Because each test device is capable of simulating real TCP connections without maintaining state, the amount of TCP connections per network interface is increased over conventional test systems. As a result, TCP/IP communications devices, such as servers and server load balancers can be tested with a reduced amount of hardware.
FIG. 4 is a flow chart illustrating an exemplary process for testing a stateful communications device according to an embodiment of the present invention. Referring to FIG. 4, in step ST1, stateless and simulated stateful connections are established with a device under test. The device under test may be any type of stateful network communications device, such as an application server or a server load balancer. If the device under test is an application server, a single test system, such as test device 102 illustrated in FIG. 2 may be configured as a client and used to establish connections with the application server. If the device under test is a server load balancer, one test device 102 may be configured as a client to establish connections with the server load balancer and another test device 104 may be configured as a server farm to receive connection requests from the server load balancer. In yet another alternative implementation, multiple test devices 102 may be used to test multiple devices under test, such as a server farm.
Stateful connections with the device under test may be established using stateful TCP connection establishment procedures as described in the above-referenced TCP/IP protocol standards documents. An exemplary procedure for establishing simulated stateless TCP/IP connections with a device under test will be described in detail below with regard to FIGS. 5 and 6.
In step ST2, test device 102 requests data on the stateless and stateful connections. If the device under test is a web server, requesting data may include requesting data using the HTTP protocol. If the device under test is a server load balancer, requesting data may include requesting data from any type of application server that may be proxied by a server load balancer. In step ST3, performance and/or behavior measurements are gathered on the stateful TCP connections. As stated above, examples of such metrics include the rate of connections being dropped, the rate of retransmissions, the rate of packets being dropped, etc. In step ST4, these measurements are used to modify the behavior of the simulated stateless connections to more closely simulate live network conditions. For example, if it is determined that packets are being retransmitted a certain rate on the stateful connections, test device 102 may be configured to retransmit packets at the same rate. If the device under test is a server load balancer and the device on the other side of the server load balancer is test device 104, programmable stateless packet processor 110 of test device 104 may be configured to retransmit data packets to test device 102. Test device 102 may be configured by its local TCP AMP controller 112 to disregard retransmitted packets.
Since programmable stateless packet processor 110 only reacts to inbound packets, some independent mechanism must be used to initiate a sequence of response packets. One method for initiating a response is by generating a “synchronous stream” of SYN packets using traditional packet-blaster capability that may be available in TX FPGA 204. This sync stream can generate packets at up to wire speed with extremely precise timing of gaps between packets (fractions of a microsecond precision). In a typical test, a sync stream will be configured to kick off the pseudo-sessions. The rate will be programmed according to the test that a user wants to perform.
One exemplary measurement that a user may want to determine in testing a device or a network is the number of sessions of a given type that can be handled at a given tolerable drop rate. For example, an SLB manufacturer might want to know how many HTTP GETs of a particular average size (or mix) can be done per second before their device starts dropping packets (due to buffers filling, for example).
The measured retransmit rate from the full stack in software can be used to change the rate of the sync stream on the stateless connections (continuously without stopping/restarting the test) until the desired drop rate is achieved (in this case, zero—but in practicality it will be some small percentage). This is much more efficient than other methods which require a linear or binary search to “home in” on the maximum rate achievable at some drop rate. A search algorithm like this would require running large numbers of tests in succession at different initial rates. The present invention thus avoids these difficulties associated with conventional test methods.
Although in the example illustrated in FIG. 4, the present invention uses measurements taken on stateful connections to modify the behavior of tests executing on stateless connections, the present invention is not limited to such an embodiment. For example, in an alternate embodiment, the present invention may include utilizing measurements taken on the stateless connections to modify the behavior of the stateless connections. In yet another alternative embodiment, the present invention may include using measurements taken on both the stateless and stateful connections to modify the behavior of the stateless connections. The behavior of the stateful connections may also be modified. Any combination of using feedback on the stateless and stateful connections to modify the behavior of the stateless and/or the stateful connections is intended to be within the scope of the invention.
In yet another alternative embodiment, the present invention may include a method and a system for testing a device under test using programmable stateless TCP processor 110 without using feedback. FIG. 5A is a flow chart illustrating exemplary operations performed by a programmable stateless packet processor according to an embodiment of the present invention. Referring to FIG. 5, in step ST1, programmable stateless packet processor 110 receives a packet from a device under test. In steps ST2 and ST3, programmable stateless packet processor 110 determines whether a response is required for the packet. For example, if the packet is a SYN packet, programmable stateless packet processor may determine that a SYN plus ACK is required in order to establish a simulated TCP connection with the device under test. If a response is not required for a received packet, control returns to step ST1 where programmable stateless packet processor 110 waits for the next packet.
If programmable stateless packet processor 110 determines that a response is required for the received packet, programmable stateless packet processor 110 prepares a response packet based on the information in the received packet. For example, in step ST4, programmable stateless packet processor 110 swaps the source and destination addresses in the IP and Ethernet headers of the received packet, assuming Ethernet is the underlying communication medium. In step ST5, programmable stateless packet processor 110 sets the appropriate bits in the TCP and network headers. This step may include computing header checksums, inserting the correct sequence number value based on the received sequence number, inserting the correct value in the TCP CODE BITS field, etc. The type of response packet may be determined based on the fields in the received packet. For example, if the CODE BITS field in the TCP header of the received packet indicates that the received packet is a SYN packet, then programmable stateless packet processor 110 changes the bits in the CODE BITS field of the outgoing packet to indicate that the packet is a SYN plus ACK. In another example, if the incoming packet contains data, programmable stateless packet processor 110 may set the appropriate bits in the CODE BITS field of the outgoing packet to indicate that the outgoing packet contains an acknowledgement.
Once the packet is constructed, in step ST6, the packet is sent to the device under test. Thus, as illustrated in FIG. 5, a programmable stateless packet processor according to an embodiment of the present invention is capable of formulating a response packet based on a receive packet without maintaining any state regarding a previously received packet.
In order to efficiently respond to received packets in a stateless manner, programmable stateless packet processor may utilize a number of data structures in order to classify and prepare responses to incoming packets. In one exemplary embodiment, programmable stateless packet processor 110 utilizes a packet classification table to classify incoming packets, a response table to determine responses for each packet classification, and a packets table to determine a packet format for each response type. FIG. 5B schematically illustrates exemplary data structures that may be used by programmable stateless packet processor 110 in classifying packets and determining the appropriate responses. Referring to FIG. 5B, packet classifications table 500 contains packet classification identifiers or pointers and corresponding offsets and patterns associated with each identifier. For example, packet classification table 500 may classify the following types of TCP packets:

    
    
        SYN
        SYNACK
        ACK
        ACK With GET
        FIN
        FINACK
        RST
    
    


Packet classification table 500 may contain bit patterns and offsets for each of the above-listed packet types.
The packet classification identifiers extracted from packet classification table 500 may be used to locate responses in response table 502. There may be multiple responses in response table 502 corresponding to each packet classification type. In a situation where there are multiple responses for a given packet classification type, the responses may be ordered and programmable stateless packet processor 502 may execute the responses in sequence. In response table 502, each response may include a packet classification identifier, a starting packet identifier, the number of packets to be included in the response, and instructions for determining acknowledgement and sequence numbers to be included in the response packet.
Each packet identifier in response table 502 may be used to locate a corresponding packet template in packet table 504. Packet table 504 may contain templates for various types of response packets, such as SYN packets, ACK packets, data packets, etc. These response templates may be used to build outgoing packets based on data extracted from received packets in the manner discussed above with regard to FIG. 5A. There may be multiple packets corresponding to each packet identifier.
In operation, when programmable stateless packet processor 110 receives a packet, it searches the packet for various patterns located at various offsets according to packet classification table 502. In response to locating a matching pattern, programmable stateless packet processor 110 uses extracts the packet classification ID and uses this value to obtain a response from response table 502. Programmable stateless packet processor 110 uses information extracted from response table 502 to extract a template from packets table 504. Programmable stateless packet processor 110 then builds the packet using the extracted template. This process may be repeated for each response stored in response table 502 for the given packet type and each packet in packets table 504 until the desired packet is sent.
FIG. 6 is a message flow diagram illustrating messages that may be sent between a programmable stateless packet processor 110 of test device 102 and a server 250 in an HTTP GET transaction. In line 1 of the message flow diagram, programmable stateless packet processor 110 formulates and sends a SYN packet to server 250. Unlike a full TCP/IP client, programmable stateless packet processor of test device 102 preferably does not maintain any state about having sent the SYN packet. In line 2 of the message flow diagram, server 250 receives a SYN packet and sends a SYN plus ACK. In line 3 of the message flow diagram, programmable stateless packet processor receives the SYN plus ACK, determines that an ACK is required based only on the received packet, and sends the ACK. In line 4 of the message flow diagram, server 250 considers the connection with test device 102 to be open. Because test device 102 preferably does not maintain connection state information, test device 102 does not know whether the connection is open. However, in the scenario illustrated in FIG. 6, test device 102 assumes that the connection is open after sending the ACK in line 3.
In line 5 of the message flow diagram, programmable stateless packet processor 110 of test device 102 sends a TCP segment containing an acknowledgement plus an HTTP GET request to server 250 to request data from server 250. In line 6 of the message flow diagram, server 250 receives the HTTP GET message, extracts the requested data, and sends the requested data to test device 102. In line 7 of the message flow diagram, test device 102 receives the data and formulates a response packet based on the data packet. In this case, the response packet is an ACK packet.
In line 9 of the message flow diagram, programmable stateless packet processor 110 of test device 102 sends a FIN plus ACK packet to server 250 to initiate a connection close. In line 10 of the message flow diagram, server 250 receives the FIN and sends an ACK to the FIN. In line 11 of the message flow diagram, programmable stateless packet processor 110 of test device 102 receives the ACK. Because the ACK does not include any data in this example, programmable stateless packet processor 110 of test device 102 determines that no response is required. In line 12 of the message flow diagram, server 250, sends a FIN plus ACK packet to test device 102 to instruct the test system to close its connection. In line 13 of the message flow diagram, programmable stateless packet processor 110 of test device 102 receives the SYN plus ACK packet. Since programmable stateless packet processor 110 does not know that the connection is open, programmable stateless packet processor 110 simply sends an acknowledgement to the FIN packet. In line 14 of the message flow diagram, server 250 receives the FIN packet, and closes and releases resources for its local connection.
Multiple simulated connections and HTTP requests may be concurrently initiated with a device under test by repeating the steps illustrated in FIG. 6 for each simulated connection. Utilizing HTTP to test stateful network communications devices is desirable because HTTP is the primary protocol used by web browsers to obtain web pages on the Internet. However, as stated above, the present invention is not limited to using HTTP to test stateful network communications devices. Any stateful application may be used.
Test Scenarios
Table 2 shown below illustrates exemplary metrics that may be used to test a device under test, such as a server load balancer or an application server, such as a web server.







TABLE 2







Test Scenarios









Metric
How Measured
Typical Values





Maximum
Client application must generate multiple
50,000-1,000,000


concurrent
requests concurrently and/or before previous


sessions
requests complete. Test system must maintain



count of how many requests are outstanding



(i.e.: TCP connection opened but not closed)



at any instant in time.


Maximum
Client application must generate large number
10,000-250,000


sessions per
of requests in parallel and in rapid succession.


second
Test system must maintain count of requests



and responses per second.


Maximum
Perform multiple session/second tests with
Variable


sessions per
increasing numbers of concurrent sessions


second as function
already open


of concurrent


sessions









An exemplary procedure for performing each of the test metrics illustrated in Table 2 will now be described.

    
    
        1. Set up client (or simulated client) applications. Enough clients must be set up to generate the maximum number of sessions/second or the total concurrent sessions, whichever is greater. For example, if general purpose PCs are being used as host processors in implementing the test, about 2,000 sessions/second will be generated by each machine using HTTP. Configuration information for this test scenario includes:
        
            a. IP addresses of clients
            b. Names or IP addresses of server
            c. If servers are not on same network as clients, the IP address of the gateway to be used to reach the servers from the client network
            d. The pages to be requested (for HTTP)
            e. Whether to use HTTP/1.0 (close session after each page) or HTTP/1.1 (keep session open for multiple page requests)
            f. Other application-specific information
        
        
        2. Set up server applications. Enough servers must be set up to respond to the number of requests/second that will be generated or to maintain the maximum number of concurrent sessions, whichever is greater.
        3. Set up instrumentation to measure all desired metrics. This may be part of client applications, server applications or a passive monitoring device.
        4. Execute test.
    
    


FIG. 7 is a screen shot illustrating an exemplary configuration screen of a test system according to an embodiment of the present invention. In FIG. 7, test screen 300 includes a first input area 302 allow a user to select the total number of simulated clients and the total number of concurrent sessions. Input area 304 allows the user to input the IP address, the gateway address, and the sub-net address for the first client used in the test. Input area 306 allows the user to input the IP address, gateway address, and sub-net mask of the first server to be used in the test.
A system for testing stateful network communications devices according to an embodiment of the present invention may collect and display statistics for each test performed. FIG. 8 is a screen shot illustrating exemplary connection rate data collected by a test system according to an embodiment of the present invention. In FIG. 8, the connection rate data includes page requests per second, connections requested per second, concurrent sessions, page failure responses per second, pace responses per second, and connections accepted per second. These and other measurements may be collected, displayed to the user in an easily understood format, and used to evaluate the performance of a device under test.
Performance Comparison
A system for testing a stateful network communications device according to the present invention achieves higher performance at a lower cost than conventional systems. Depending on how stateful the device being tested is, and how much of a full TCP stack it implements, there are several alternative means of generating adequate traffic to test the performance limits of the device. Each method presents a tradeoff between cost, complexity and realism. Determining which method is the least expensive acceptable method depends on validating the test results for each method against those obtained with real traffic. As will be seen in Table 3 shown below, a system for testing stateful network communications devices according to the present invention gives better performance per unit cost over conventional test systems.
In Table 3, the second to last column includes cost and performance data for a system for testing a stateful network communications device according to an embodiment of the present invention. The remaining columns include cost and performance data for conventional test systems. It can be seen from the last row in Table 3 that the cost for testing one million sessions per second using a system for testing a stateful network communications device according to an embodiment of the present invention is $80,000 using current hardware as compared to $1 million for full TCP stack implementations. Stateless implementations, such as packet blasters are cheaper. However, as discussed above, such devices are unsuitable for testing stateful devices, such as next generation server load balancers. Thus, test systems according to embodiments of the present inventions provide the same testing functionality as full-stack devices at a much lower cost.







TABLE 3







TCP Traffic Generation Capabilities for Various Methods














HW-based
SW-based
HW/SW
CPU-



Traditional
Stateless
Stateless
Hybrid
based



Packet
Packet
Packet
Amplified
Full


TCP/Application Capability
Blaster
Processor
Processor
TCP
TCP/IP





MAC DA/SA (swap)

X (1)
X
X
X


IP DA/SA (swap)

X (1)
X
X
X


TCP src/dst port (swap)

X (1)
X
X
X


TCP control bits (change

X (1, 2)
X (2)
X (4)
X


appropriately)


TCP Sequence # (compute)


X
X
X


TCP Dynamic Window Size



X (4)
x


TCP Retransmit



X (4)
x


Fragmentation



X (4)
x


(create/reassemble)


HTTP Get Response (static


X (3)
X (4)
x


page)


HTTP Cookie (static
X
X
X
X
X


request)


HTTP Cookie (dynamic



X (4)
x


accept/transmit)


TCP open/close per sec, per
35
35
 10
25
2


port, thousands (5)


Est Cost to test IM
57
57
200
80
1000


sessions/sec, $k (6)





(1) limitations vary by implementation


(2) fixed state sequence only


(3) limited number of static URL/page pairs


(4) not handled individually on a per-session basis


(5) on 100 mbps full duplex Ethernet link, mid-range estimate (varies by implementation & hardware)


(6) based on $2,000 per port or PC (for SW stack)






It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.

## Claims

1. A method for testing a stateful network communications device, the method comprising:
establishing a plurality of stateful connections with a device under test
establishing a plurality of simulated stateless TCP connections with the device under test
sending packets to the device under test over the simulated stateless TCP and stateful connections
receiving responses from the device under test over the simulated stateless TCP and stateful connections
obtaining measurements for at least one of the simulated stateless TCP and stateful connections.

2. The method of claim 1 wherein establishing stateful connections with a device under test includes establishing full-TCP-stack connections with the device under test.

3. The method of claim 1 wherein establishing stateful connections with a device under test includes establishing stateful connections with an application server.

4. The method of claim 1 wherein establishing stateful connections with a device under test includes establishing stateful connections with a server load balancer.

5. The method of claim 1 wherein establishing simulated stateless TCP connections with the device under test includes emulating TCP sequence numbering, retransmission, and flow control on a packet by packet basis on each of the stateless connections.

6. The method of claim 1 wherein establishing simulated stateless TCP connections includes simulating TCP connection establishment and termination without maintaining state.

7. The method of claim 1 wherein establishing simulated stateless TCP connections is performed at a variable rate to more closely simulate live connections.