![]() Tweaking TCP settingsĪnother step to troubleshoot TCP retransmission is to tweak TCP settings. Network administrators can use tools like Wireshark to capture packets and analyze them to determine the source of the problem. Packet captures can provide valuable information about the network traffic, which can help identify the root cause of the issue. The first step to troubleshoot TCP retransmission is to analyze packet captures. ![]() There are several technical steps that network administrators can take to troubleshoot TCP retransmission issues. Technical Steps to Troubleshoot TCP Retransmission These issues can have severe consequences for business productivity, so it is essential to address TCP retransmission as soon as possible. This issue can also increase network latency, causing delays in data transmission, which can disrupt critical applications. Excessive retransmission can cause data loss, which can result in slow data transfer rates and reduced throughput. Understanding the impact of excessive retransmission on network performanceīefore delving into the technical steps to troubleshoot TCP retransmission, it is important to understand the impact that excessive retransmission can have on network performance. Below, I will outline some technical steps that can help to troubleshoot this issue. To avoid these consequences, it is necessary to troubleshoot the TCP retransmission issue and resolve it as soon as possible. This issue can also cause network timeouts, which can disrupt critical applications. For instance, it can result in slow data transfer rates, increased latency, and reduced throughput. When TCP retransmission occurs, it can cause a range of problems for network performance. This can happen for a variety of reasons, including: TCP retransmission occurs when an acknowledgment of a transmitted packet is not received by the sender within a specific time frame. TCP Retransmission: Causes and Consequences I strongly recommend checking the CCIE Enterprise Course for those who want to learn more about this topic. In this post, I will discuss the causes and consequences of TCP retransmission and provide technical steps to troubleshoot this issue. This problem can be frustrating for network administrators, as it can result in slow network performance and reduced productivity. Any additional ideas would be most appreciated.As a certified network security engineer, I have noticed that TCP retransmission issues often plague many networks. At the end, the program reported less than 1% packet loss. To test this, I ran twelve hours of pings. This leaves just packet loss as a likely cause. Over the duration of that sample, the average bandwidth usage was 98kbps, so it was definitely not congested. To my surprise, that 10 minute sample showed the TCP retransmit rate was nearly identical to all the other captures - 58%. I took that opportunity to take a Wireshark capture of the network when it wasn't congested. The captain asked me to disable the guest access to the Internet during a drill. The other things helped a little bit, but not enough to make a real difference.īut this weekend I was put back to square one. My first thought was that it was a congestion issue, so I pursued various solutions to this (blocking high bandwidth services like video chatting and streaming, bugging the corporate office to pay for a bigger pipe, etc). The wireless network is provided by numerous Cisco APs (signal propagation in a steel ship at sea is terrible). The wired network is run by a series of Cisco 2900 gigabit switches. ![]() Both VLANs have wired and wireless clients. Both VLANs are piped into a SonicWall TZ 215 (running SonicOS Enhanced 5.8.1.2-6o) which controls the pipe to the Internet. The network consists of two VLANs (one for ship's computers, and the other for guests). At the moment, we have about 300 people aboard, all sharing that pipe. Being a satellite link, it runs about 650ms ping times. ![]() Unfortunately, the bandwidth costs for this type of link are prodigious, so we're stuck with a 1Mbps down / 512kbps up connection. It uses a satellite link to communicate with the Internet. The network in question is aboard a ship at sea. ![]() Let me lay out our situation, and I would love to hear from people more knowledgeable than myself on other directions of inquiry to resolve the problem. What's confusing me is that as far as I know, there are only two reasons for this sort of issue: a flaky link that drops packets, and congestion. 36 samples (taken with Wireshark 1.10.8 running on 32-bit Windows 7) totaling a little over seven hours, ranging between 2 and 53 minutes each shows retransmits occupying between 43 and 61 percent of the total ingress bandwidth. I've been attempting to troubleshoot a network issue that presents with very high rate of TCP retransmits. ![]()
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