https://github.com/lpcodes/identifying-and-troubleshooting-common-tcp-issues-with-wireshark
How to identify the problem using Wireshark TCP logs and suggest potential resolutions.
https://github.com/lpcodes/identifying-and-troubleshooting-common-tcp-issues-with-wireshark
network-analysis osi tcp troubleshoot troubleshooting wireshark
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How to identify the problem using Wireshark TCP logs and suggest potential resolutions.
- Host: GitHub
- URL: https://github.com/lpcodes/identifying-and-troubleshooting-common-tcp-issues-with-wireshark
- Owner: LpCodes
- Created: 2024-07-14T07:05:20.000Z (about 1 year ago)
- Default Branch: main
- Last Pushed: 2024-07-14T07:05:49.000Z (about 1 year ago)
- Last Synced: 2025-01-19T12:50:04.456Z (9 months ago)
- Topics: network-analysis, osi, tcp, troubleshoot, troubleshooting, wireshark
- Homepage: https://lpcodes.github.io/Identifying-and-Troubleshooting-Common-TCP-Issues-with-Wireshark/
- Size: 5.86 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
### Identifying and Troubleshooting Common TCP Issues with Wireshark
How to identify the problem using Wireshark logs and suggest potential resolutions.
### 1. Connection Establishment Issues
**Scenario**: Clients are unable to establish a connection to the server.
**Symptoms**: SYN packets sent by the client do not receive SYN-ACK responses from the server.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
1 0.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
2 1.000000 192.168.1.2 192.168.1.1 TCP 60 [TCP Retransmission] 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
3 2.000000 192.168.1.2 192.168.1.1 TCP 60 [TCP Retransmission] 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
```
**Explanation**:
- **Packet 1**: The client (192.168.1.2) sends a SYN packet to the server (192.168.1.1).
- **Packets 2 & 3**: The client retransmits the SYN packet because it did not receive a SYN-ACK response.
**Resolution**:
- **Verify Server Availability**: Ensure the server is up and running.
- **Check Firewall Settings**: Confirm that there are no firewall rules blocking the connection.
- **Network Configuration**: Check for any network misconfigurations or issues with routing.
### 2. Retransmissions and Timeouts
**Scenario**: Delays in data transmission, leading to retransmitted packets.
**Symptoms**: Packets are retransmitted due to timeouts.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
10 3.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [PSH, ACK] Seq=1 Ack=1 Win=64240 Len=50
11 3.100000 192.168.1.1 192.168.1.2 TCP 60 [TCP Dup ACK 10#1] 80 → 49716 [ACK] Seq=1 Ack=1 Win=64240 Len=0
12 4.000000 192.168.1.2 192.168.1.1 TCP 60 [TCP Retransmission] 49716 → 80 [PSH, ACK] Seq=1 Ack=1 Win=64240 Len=50
```
**Explanation**:
- **Packet 10**: The client sends data (PSH, ACK) to the server.
- **Packet 11**: The server sends a duplicate ACK, indicating it didn't receive the expected data.
- **Packet 12**: The client retransmits the data.
**Resolution**:
- **Network Stability**: Ensure that the network is stable and free from high latency.
- **Packet Loss**: Check for packet loss and resolve any underlying issues causing it (e.g., faulty hardware, congested links).
### 3. Duplicate ACKs and Fast Retransmits
**Scenario**: Multiple duplicate ACKs received, leading to fast retransmits.
**Symptoms**: Multiple duplicate ACKs and fast retransmissions occur.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
20 5.000000 192.168.1.1 192.168.1.2 TCP 60 [TCP Dup ACK 19#1] 80 → 49716 [ACK] Seq=1 Ack=51 Win=64240 Len=0
21 5.000500 192.168.1.1 192.168.1.2 TCP 60 [TCP Dup ACK 19#2] 80 → 49716 [ACK] Seq=1 Ack=51 Win=64240 Len=0
22 5.001000 192.168.1.2 192.168.1.1 TCP 60 [TCP Fast Retransmission] 49716 → 80 [PSH, ACK] Seq=51 Ack=1 Win=64240 Len=50
```
**Explanation**:
- **Packets 20 & 21**: The server sends duplicate ACKs for the same sequence number, indicating a missing segment.
- **Packet 22**: The client performs a fast retransmission of the missing segment.
**Resolution**:
- **Network Reliability**: Improve network reliability to reduce the chances of packet drops.
- **Hardware Issues**: Replace or repair any faulty network hardware that may be causing packet corruption or loss.
### 4. TCP Window Size Problems
**Scenario**: Reduced throughput due to small TCP window size.
**Symptoms**: Slow data transfer rates.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
30 6.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [ACK] Seq=101 Ack=101 Win=256 Len=0
31 6.100000 192.168.1.1 192.168.1.2 TCP 60 80 → 49716 [PSH, ACK] Seq=101 Ack=101 Win=256 Len=50
```
**Explanation**:
- **Packets 30 & 31**: The TCP window size is set to a small value (256), limiting the amount of data that can be sent before waiting for an acknowledgment.
**Resolution**:
- **Window Size Adjustment**: Adjust TCP window size settings on the endpoints to a suitable value to maximize throughput.
- **Network Latency**: Ensure that network latency is minimized to allow for larger window sizes to be effective.
### 5. TCP Reset (RST) Issues
**Scenario**: Unexpected termination of connections.
**Symptoms**: TCP connections are reset unexpectedly.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
40 7.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [RST, ACK] Seq=151 Ack=151 Win=0 Len=0
```
**Explanation**:
- **Packet 40**: The client sends a TCP reset (RST) packet, terminating the connection.
**Resolution**:
- **Application Errors**: Check for application errors or misconfigurations that may be causing the connection to reset.
- **Protocol Violations**: Ensure that there are no protocol violations causing the reset.
### 6. Throughput Analysis
**Scenario**: Low data transfer rates affecting application performance.
**Symptoms**: Data transfer rates are significantly lower than expected.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
50 8.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [ACK] Seq=201 Ack=201 Win=64240 Len=1000
51 8.100000 192.168.1.1 192.168.1.2 TCP 60 80 → 49716 [ACK] Seq=201 Ack=1201 Win=64240 Len=0
52 8.200000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [ACK] Seq=1201 Ack=201 Win=64240 Len=1000
```
**Explanation**:
- **Packets 50 & 52**: The client sends data segments of 1000 bytes each.
- **Packet 51**: The server acknowledges the data received.
**Resolution**:
- **Bottleneck Identification**: Identify and resolve any bottlenecks in the network path.
- **Network Optimization**: Optimize network settings and configurations to improve data transfer rates.
### 7. Using Statistics and Graphs
Wireshark provides powerful statistical tools:
- **TCP Stream Graphs**: `Statistics > TCP Stream Graphs`
- **Time-Sequence Graphs**: Visualize sequence numbers over time.
- **Round-Trip Time Graphs**: Analyze round-trip times for packets.
- **Throughput Graphs**: Measure data transfer rates.
- **IO Graphs**: `Statistics > IO Graphs` for visualizing overall traffic patterns and identifying spikes or drops in traffic.
### 8. Saving and Exporting Logs
- **Save Capture**: `File > Save As...` to save your captured traffic for later analysis.
- **Export Specific Packets**: `File > Export Specified Packets...` to export filtered packets of interest.
### 9. Practical Examples and Case Studies
#### Example 1: Slow Website Load
**Scenario**: Users report that a website is loading slowly.
**Capture**: Filter HTTP traffic using `tcp.port == 80`.
**Analysis**:
1. **Check TCP Handshake**: Ensure that the handshake completes successfully without delays.
2. **Look for Retransmissions**: Identify any retransmitted packets that may be causing delays.
3. **Analyze Throughput**: Use throughput graphs to see if data transfer rates are lower than expected.
**Resolution**:
- **Server Performance**: Ensure that the server has sufficient resources and is not overloaded.
- **Network Congestion**: Investigate and mitigate any network congestion issues.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
1 0.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
2 0.001000 192.168.1.1 192.168.1.2 TCP 60 80 → 49716 [SYN, ACK] Seq=0 Ack=1 Win=64240 Len=0 MSS=1460
3 0.002000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [ACK] Seq=1 Ack=1 Win=64240 Len=0
4 0.010000 192.168.1.2 192.168.1.1 HTTP 500 GET /index.html HTTP/1.1
5 0.100000 192.168.1.1 192.168.1.2 TCP 60 [TCP Retransmission] 80 → 49716 [PSH, ACK] Seq=1 Ack=1 Win=64240 Len=50
6 0.200000 192.168.1.1 192.168.1.2 HTTP 1000 HTTP/1.1 200 OK
```
#### Example 2: Intermittent Connectivity
**Scenario**: Users experience intermittent connectivity to a service.
**Capture**: Filter traffic from affected clients.
**Analysis**:
1. **Check for Resets**: Look for TCP reset packets indicating connection drops.
2. **Identify Timeouts**: Identify any packets that are retransmitted due to timeouts.
**Resolution**:
- **Hardware Issues**: Check for and replace any faulty network hardware.
- **Network Configuration**: Ensure there are no misconfigurations causing intermittent drops.
**Sample Log**:
```
No. Time Source Destination Protocol Length Info
1 0.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
2 0.001000 192.168.1.1 192.168.1.2 TCP 60 80 → 49716 [SYN, ACK] Seq=0 Ack=1 Win=64240 Len=0 MSS=1460
3 0.002000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [ACK] Seq=1 Ack=1 Win=64240 Len=0
4 5.000000 192.168.1.2 192.168.1.1 TCP 60 49716 → 80 [RST, ACK] Seq=1001 Ack=1001 Win=0 Len=0
5 5.100000 192.168.1.2 192.168.1.1 TCP 60 [TCP Retransmission] 49716 → 80 [SYN] Seq=0 Win=64240 Len=0 MSS=1460
```
###
If you have any suggestions, improvements, or additional examples that you would like to share, please help to contibute.