Tcpreplay Bug Packet Sending Exited With Error Using --xdp

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This article details a bug encountered while using Tcpreplay version 4.5.2-beta1 with the --xdp option. The bug results in the error message "Packet sending exited with error" and prevents packets from being sent. This issue was observed on Ubuntu 24.04 within a vagrant-libvirt virtual machine using an Intel Corporation Ethernet Controller XL710 for 40GbE QSFP+. This comprehensive report provides a detailed account of the bug, the steps to reproduce it, the expected behavior, and the system configuration used during testing. Understanding the intricacies of this bug is crucial for developers and users who rely on Tcpreplay for network traffic analysis and simulation. This article aims to provide a clear and thorough explanation of the issue, making it easier for the Tcpreplay community to address and resolve it. By documenting the problem in detail, we hope to contribute to the ongoing improvement and stability of Tcpreplay.

Bug Description

The Tcpreplay bug occurs when the --xdp option is used, preventing packet transmission and resulting in the error message "Packet sending exited with error." This issue was identified while testing Tcpreplay version 4.5.2-beta1 on an Ubuntu 24.04 system running within a vagrant-libvirt virtual machine. The underlying network interface card (NIC) is an Intel Corporation Ethernet Controller XL710 for 40GbE QSFP+. This bug significantly impacts the usability of Tcpreplay in XDP (eXpress Data Path) mode, which is designed to provide high-performance packet processing at the network interface level. Without a functioning XDP mode, users are unable to leverage the performance benefits of XDP for traffic replay and simulation. This issue affects various use cases, including network performance testing, security vulnerability analysis, and network application development. It is essential to address this bug to ensure that Tcpreplay can effectively support XDP-based network deployments and research.

Steps to Reproduce

To reproduce this Tcpreplay bug, follow these steps:

  1. Download Tcpreplay version 4.5.2-beta1.
  2. Build Tcpreplay from source, adhering to the instructions provided in the documentation.
  3. Execute the following command with appropriate privileges: sudo tcpreplay --xdp -i eth1 some-pkts.pcap, replacing eth1 with the relevant network interface and some-pkts.pcap with a valid packet capture file.
  4. Observe the error message "Packet sending exited with error" in the output.

This step-by-step reproduction process ensures that the bug can be consistently reproduced across different environments, which is crucial for effective debugging and resolution. The use of a specific Tcpreplay version (4.5.2-beta1) and a clear set of instructions helps isolate the issue and prevent variations in testing conditions from masking the problem. By following these steps, developers and users can verify the existence of the bug on their systems and contribute to the troubleshooting effort. The ability to reliably reproduce a bug is a fundamental requirement for any software development process, and this detailed guide aims to facilitate that for the Tcpreplay community.

Expected Behavior

The expected behavior of Tcpreplay when using the --xdp option is that it should function similarly to its operation without the --xdp flag, successfully transmitting packets from the provided pcap file through the specified network interface. In XDP mode, Tcpreplay should leverage the kernel's eXpress Data Path (XDP) capabilities to achieve high-performance packet injection directly at the network interface card (NIC) level. This means that packets should be processed and transmitted with minimal overhead, resulting in faster and more efficient traffic replay. The absence of the "Packet sending exited with error" message is also a key aspect of the expected behavior. When Tcpreplay operates correctly in XDP mode, it should provide detailed statistics on the number of packets sent, the transmission rate, and any potential errors encountered during the process. This information is crucial for users to verify that the traffic replay is occurring as intended and to diagnose any network performance issues. The deviation from this expected behavior, as described in the bug report, highlights a critical issue that needs to be addressed to fully utilize the benefits of XDP in Tcpreplay.

Observed Behavior and Error Message

When running Tcpreplay with the --xdp option, the observed behavior is that no packets are sent, and the process terminates with the error message "Packet sending exited with error". This Tcpreplay error indicates a critical failure in the packet injection process, preventing Tcpreplay from functioning as intended in XDP mode. The error message suggests that the issue occurs during the attempt to send packets, potentially related to the setup of the XDP program or the interaction with the network interface. This failure prevents users from leveraging the performance benefits of XDP for high-speed traffic replay and simulation. Further investigation is required to pinpoint the exact cause of the error, which could involve issues with the XDP program loading, memory allocation, or network interface configuration. The presence of this error message highlights a significant problem in Tcpreplay's XDP implementation, which needs to be addressed to ensure reliable and efficient packet transmission.

System Information

The following system information provides context for the Tcpreplay bug:

  • Operating System: Ubuntu 24.04 in vagrant-libvirt's vm (kvm qemu)
  • OS Version:
    • 24.04.2 LTS (Noble Numbat)
    • 6.8.0-64-generic
  • Tcpreplay Version: 4.5.2-beta1
  • NIC: Intel Corporation Ethernet Controller XL710 for 40GbE QSFP+ (rev 02)

This system configuration is essential for understanding the environment in which the bug was encountered. The use of Ubuntu 24.04 within a virtualized environment (vagrant-libvirt with kvm qemu) and a specific kernel version (6.8.0-64-generic) may have implications for the bug's behavior. The network interface card (NIC), an Intel Corporation Ethernet Controller XL710 for 40GbE QSFP+ (rev 02), is a high-performance NIC that supports advanced features like XDP. The interaction between Tcpreplay, the operating system, the virtualization layer, and the NIC driver could be contributing factors to the bug. By documenting these details, we provide a comprehensive view of the system setup, which can aid in identifying potential compatibility issues or driver-related problems. This information is crucial for developers to replicate the bug in a similar environment and effectively troubleshoot the issue.

Tcpreplay Version Details

The Tcpreplay version in use is 4.5.2-beta1, with the following details:

tcpreplay version: 4.5.2-beta1 (build git:v4.5.2-beta1) (debug)
Copyright 2013-2024 by Fred Klassen <tcpreplay at appneta dot com> - AppNeta
Copyright 2000-2012 by Aaron Turner <aturner at synfin dot net>
The entire Tcpreplay Suite is licensed under the GPLv3
Cache file supported: 04
Not compiled with libdnet.
Compiled against libpcap: 1.10.4
64 bit packet counters: enabled
Verbose printing via tcpdump: enabled
Packet editing: disabled
Fragroute engine: disabled
Injection method: PF_PACKET send()
Not compiled with netmap
Optional injection method: AF_XDP

These details provide crucial information about the Tcpreplay build configuration and capabilities. The version number (4.5.2-beta1) indicates that this is a pre-release version, which may contain known or unknown bugs. The build information (build git:v4.5.2-beta1) specifies the exact commit or tag used to build the software, allowing for precise replication of the environment. The copyright notices acknowledge the contributors and the licensing terms (GPLv3). The output also shows whether certain features or libraries are enabled or disabled. For example, it indicates that the software was compiled against libpcap 1.10.4, which is a critical library for packet capture and injection. The lines "Injection method: PF_PACKET send()" and "Optional injection method: AF_XDP" confirm that both the traditional PF_PACKET and the AF_XDP injection methods are available. However, the bug report suggests that the AF_XDP method is not functioning correctly. This detailed version information is essential for developers to understand the specific Tcpreplay build being used and to identify any potential configuration issues or missing dependencies.

Additional Context and Kernel Logs

This issue appears to be a Tcpreplay bug duplication of #898, but with a different NIC. However, no error messages are present in kern.log. This suggests that the problem might not be directly related to kernel-level errors or driver issues, but rather to a specific interaction between Tcpreplay's XDP implementation and the NIC. The absence of error messages in kern.log makes debugging more challenging, as it eliminates one potential source of information. It also indicates that the issue might be occurring within the user space components of Tcpreplay, rather than at the kernel level. This could involve problems with memory allocation, XDP program loading, or packet processing within Tcpreplay itself. Further investigation is needed to identify the root cause of the problem, potentially involving the use of debugging tools and techniques to trace the execution flow of Tcpreplay and examine its internal state. The fact that this issue is similar to #898, but with a different NIC, suggests that there might be a broader problem affecting multiple NICs or system configurations.

The kernel logs (/var/log/kern.log) do not show any relevant error messages:

❯ tail /var/log/kern.log
2025-07-17T09:55:44.974345+00:00 vm-sec-4 kernel: ipmi_si: Unable to find any System Interface(s)
2025-07-17T09:55:45.062374+00:00 vm-sec-4 kernel: Bluetooth: Core ver 2.22
2025-07-17T09:55:45.062400+00:00 vm-sec-4 kernel: NET: Registered PF_BLUETOOTH protocol family
2025-07-17T09:55:45.062403+00:00 vm-sec-4 kernel: Bluetooth: HCI device and connection manager initialized
2025-07-17T09:55:45.062405+00:00 vm-sec-4 kernel: Bluetooth: HCI socket layer initialized
2025-07-17T09:55:45.062407+00:00 vm-sec-4 kernel: Bluetooth: L2CAP socket layer initialized
2025-07-17T09:55:45.062408+00:00 vm-sec-4 kernel: Bluetooth: SCO socket layer initialized
2025-07-17T09:55:45.720678+00:00 vm-sec-4 kernel: virtio_net virtio2 eth0: entered promiscuous mode
2025-07-17T10:57:42.115553+00:00 vm-sec-4 kernel: i40e 0000:03:00.0 eth1: entered promiscuous mode
2025-07-17T10:57:42.128777+00:00 vm-sec-4 kernel: i40e 0000:03:00.0 eth1: left promiscuous mode

The user is seeking guidance on where to obtain more debug information for this error. This is a crucial step in the troubleshooting process, as more detailed logs or debugging output can provide valuable insights into the root cause of the problem. Potential sources of debug information include Tcpreplay's own logging mechanisms, which might be enabled through command-line options or configuration files. Additionally, using debugging tools like gdb to step through Tcpreplay's code execution can help identify the exact point where the error occurs. Examining the XDP program loading and execution process, as well as the interaction with the NIC driver, might also reveal clues. The user's question highlights the need for improved error reporting and debugging capabilities in Tcpreplay, which can help users diagnose and resolve issues more effectively.

Conclusion

In conclusion, the reported bug in Tcpreplay version 4.5.2-beta1, where the --xdp option leads to a "Packet sending exited with error" and prevents packet transmission, presents a significant challenge for users relying on XDP for high-performance traffic replay. The detailed steps to reproduce the bug, along with the system configuration and version information, provide a solid foundation for further investigation and resolution. The absence of relevant error messages in the kernel logs suggests that the issue may lie within the user space components of Tcpreplay, potentially related to memory management, XDP program loading, or interaction with the NIC driver. The user's inquiry about obtaining more debug information underscores the importance of robust error reporting and debugging tools in Tcpreplay. Addressing this bug is crucial for ensuring the reliable and efficient operation of Tcpreplay in XDP mode, which is essential for network performance testing, security vulnerability analysis, and network application development. The Tcpreplay community and developers should prioritize this issue to enhance the usability and stability of the software. Further investigation should focus on leveraging debugging tools, examining Tcpreplay's internal logs, and potentially collaborating with NIC driver developers to identify and resolve the root cause of the problem. This collaborative effort will contribute to the continued improvement and widespread adoption of Tcpreplay as a valuable tool for network traffic analysis and simulation.