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How can TCP timestamps help identify network latency?

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Network latency is the delay between sending and receiving data packets over a network. It can affect the performance and reliability of network applications and services, such as web browsing, video streaming, online gaming, and voice over IP. One way to measure and troubleshoot network latency is to use TCP timestamps, a feature of the Transmission Control Protocol (TCP) that records the time when each packet is sent and received.

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Harshvardhan Singh
Krishna Kumar Sharma

1 What are TCP timestamps?

TCP timestamps are optional fields in the TCP header that store the value of a 32-bit counter that increments every millisecond. The sender and the receiver of a TCP connection can exchange their timestamps in each packet to keep track of the round-trip time (RTT), the elapsed time between sending a packet and receiving an acknowledgment. The RTT can be used to estimate the network latency and adjust the TCP parameters, such as the retransmission timeout and the congestion window, to optimize the data transfer.

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Harshvardhan Singh
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TCP timestamps are a feature in the TCP header that allows systems to exchange information about the timing of packets. Each TCP segment includes a timestamp field, which can be used to record the time the segment was sent.

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Luiz Henrique Silveira

CTO na BRASILINE TECNOLOGIA | Especialista Fortinet FCP | FCSS (NSE4, NSE5 e 2x NSE7) | Pós gradua??o em Gest?o da Seguran?a da Informa??o
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Usada para monitorar e otimizar a performance da conex?o. Ao medir o tempo de ida e volta (RTT) de pacotes, esses carimbos permitem uma estimativa precisa da latência da rede, facilitando ajustes dinamicos nos tempos de retransmiss?o e no controle de congestionamento. Isso é essencial para manter a eficiência da comunica??o, especialmente em redes com flutua??es de latência ou congestionamento variável. A habilidade de ajustar parametros de transmiss?o em tempo real, baseando-se nos carimbos de data/hora, contribui significativamente para a estabilidade e confiabilidade das conex?es TCP, otimizando a experiência do usuário em aplica??es dependentes da internet.

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2 How to enable TCP timestamps?

TCP timestamps are not enabled by default on most operating systems, as they can increase the packet size and expose information that can be used by attackers to fingerprint the system or launch denial-of-service attacks. However, if you want to enable TCP timestamps for network analysis or monitoring purposes, you can do so by changing the configuration settings of your network interface or your TCP stack. For example, on Linux, you can use the following command to enable TCP timestamps on the eth0 interface: sudo sysctl -w net.ipv4.tcp_timestamps=1

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Harshvardhan Singh
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TCP timestamps are usually enabled by default on modern operating systems. To ensure timestamps are enabled, check the TCP Timestamp option in the TCP header during the TCP handshake. If needed, TCP timestamps can be manually enabled or disabled through system settings or configuration files.

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Luiz Henrique Silveira

CTO na BRASILINE TECNOLOGIA | Especialista Fortinet FCP | FCSS (NSE4, NSE5 e 2x NSE7) | Pós gradua??o em Gest?o da Seguran?a da Informa??o
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Embora úteis para análise e otimiza??o de desempenho de rede, sua ativa??o pode de fato aumentar o overhead de pacotes e potencialmente fornecer informa??es úteis para adversários. No Linux, por exemplo, a ativa??o é realizada via ajustes na configura??o do sistema, como o comando sudo sysctl -w net.ipv4.tcp_timestamps=1 para interfaces específicas. Essa a??o deve ser tomada com plena consciência das implica??es de seguran?a, ponderando a necessidade de dados de desempenho detalhados contra a exposi??o a possíveis vetores de ataque. Em ambientes onde a análise de desempenho é crítica, medidas adicionais de seguran?a devem ser consideradas para mitigar os riscos associados.

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3 How to capture TCP timestamps?

To capture TCP timestamps, you need a packet capture tool that can decode the TCP header and display the timestamp values. One such tool is Wireshark, a popular open-source network analyzer that can capture and analyze network traffic in real time or from saved files. Wireshark can show the TCP timestamps in the packet details pane, under the TCP section, as TSval (timestamp value) and TSecr (timestamp echo reply). You can also add these fields as columns in the packet list pane, or filter the packets by these fields using the display filter syntax: tcp.options.timestamp.tsval tcp.options.timestamp.tsecr

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Harshvardhan Singh
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Use packet capture tools like Wireshark or tcpdump to capture network traffic. Ensure that the capture includes the TCP timestamp field in the TCP header. Analyze captured packets to extract TCP timestamp information.

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Luiz Henrique Silveira

CTO na BRASILINE TECNOLOGIA | Especialista Fortinet FCP | FCSS (NSE4, NSE5 e 2x NSE7) | Pós gradua??o em Gest?o da Seguran?a da Informa??o
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Capturar carimbos de data/hora TCP efetivamente exige o uso de ferramentas avan?adas de análise de rede como o Wireshark. Esta ferramenta permite n?o apenas a captura de tráfego de rede em tempo real, mas também oferece uma análise detalhada dos cabe?alhos TCP, incluindo os valores de carimbos de data/hora. Com o Wireshark, é possível visualizar o TSval (valor do carimbo de data/hora) e o TSecr (resposta do eco do carimbo de data/hora) dentro do detalhamento de cada pacote TCP. Além disso, personalizar o painel de visualiza??o para incluir esses campos como colunas facilita o monitoramento e análise dos carimbos de data/hora em fluxos de tráfego extensos.

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4 How to calculate network latency from TCP timestamps?

To calculate the network latency from TCP timestamps, you need to subtract the timestamp value of the sender from the timestamp echo reply of the receiver, and divide the result by two. This will give you the one-way latency, or the delay between sending a packet and receiving it at the other end. You can also multiply the result by two to get the round-trip latency, or the delay between sending a packet and receiving an acknowledgment. For example, if you have a packet with a TSval of 123456 and a TSecr of 234567, the one-way latency is: (234567 - 123456) / 2 = 55555.5 milliseconds The round-trip latency is: (234567 - 123456) * 2 = 111111 milliseconds

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Harshvardhan Singh
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Calculate the Round-Trip Time (RTT) using TCP timestamps. RTT is the time taken for a packet to travel from the source to the destination and back. Subtract the timestamp from the acknowledgment (ACK) packet from the timestamp of the corresponding data packet to get the RTT. Network latency is approximately half of the RTT (considering one-way latency), as it represents the time taken for the packet to travel from the source to the destination.

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5 How to use network latency information for troubleshooting?

Network latency information can help you identify and troubleshoot various network issues, such as congestion, packet loss, misconfiguration, or malicious activity. For instance, you can compare the latency of different paths or routes to a destination to determine the optimal one. Additionally, spikes or variations in latency can be detected to indicate network congestion or instability, which can be adjusted with the TCP parameters. Furthermore, packets that are delayed or dropped due to network errors or retransmissions can be identified and investigated for a root cause. Lastly, abnormal or suspicious latency patterns that suggest network attacks or intrusions can be spotted and countermeasures taken.

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Harshvardhan Singh
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Identify latency outliers by analyzing RTT values. Higher RTT may indicate network congestion, packet loss, or other issues. Correlate latency spikes with specific events or activities on the network to pinpoint the cause. Use latency information to troubleshoot and optimize network performance, addressing any issues affecting the user experience.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Krishna Kumar Sharma
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Beyond TCP timestamps, factors like Network topology, QoS and underlying hardware also impacts the performance of the network. Diagnostic tools like Traceroute & ping complements TCP timestamp analysis and enables a thorough troubleshooting and optimisation technique.

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How can TCP timestamps help identify network latency?

1

2

3

4

5

6

1 What are TCP timestamps?

2 How to enable TCP timestamps?

3 How to capture TCP timestamps?

4 How to calculate network latency from TCP timestamps?

5 How to use network latency information for troubleshooting?

6 Here’s what else to consider

Network Security

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How can TCP timestamps help identify network latency?

1

2

3

4

5

6

1 What are TCP timestamps?

2 How to enable TCP timestamps?

3 How to capture TCP timestamps?

4 How to calculate network latency from TCP timestamps?

5 How to use network latency information for troubleshooting?

6 Here’s what else to consider

Network Security

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