IPv4: martian source a.b.c.d from w.x.y.z, on dev eth

Root Cause Analysis Report Problem Statement The network experienced intermittent connectivity issues and packet loss on a VM connected via eth5. The VM could ping its gateway but had inconsistent connectivity to remote IPs. The issue was traced to a misconfiguration on the VMware VSwitch, specifically related to port-mirroring on eth5, which caused an IP conflict. Sample Logs Provided: (use “dmesg” utility to collect sample logs)

[25480404.854672] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480404.854709] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480404.854717] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480408.897184] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480408.897210] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480408.897215] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5
[25480411.934713] IPv4: martian source 10.250.162.41 from 172.18.18.1, on dev eth5

Analysis of the Log Messages:

Log messages show repeated instances of martian packets with the source IP 10.250.162.41 coming from various IP addresses (172.18.18.1, 10.60.31.6, 10.60.31.5, 10.250.163.2, 10.250.0.38) on the network interface eth5. This suggests that packets with the source IP 10.250.162.41 are being received on eth5 from multiple different sources, which is unexpected and likely indicates a network configuration issue. Problem Analysis The issue was identified through the analysis of “martian packets” in the system logs. Martian packets are network packets with source or destination IP addresses that are considered invalid or unexpected on a given network interface. These packets are typically flagged by the kernel because they should not be routable or are coming from an unexpected source. Potential Causes

1. Incorrect Routing Configuration: There might be a routing issue causing packets to be sent to the wrong interface.
2. IP Address Conflicts: Multiple devices might be using the same IP address (10.250.162.41), leading to conflicts.
3. Network Segmentation Issues: The network might not be properly segmented, causing packets to appear on interfaces where they shouldn’t be.
4. Spoofing or Malicious Activity: There could be an attempt to spoof IP addresses on your network.

Technical Terms Explained:

• Martian Packets: Packets with invalid or unexpected IP addresses.
• Port-Mirroring: A network switch feature that copies network packets seen on one port to another port.
• ARP Table: A table used to map IP addresses to MAC addresses.
• IP Conflict: Occurs when two devices on the same network are assigned the same IP address.

Troubleshooting Steps Taken

1. Initial Observation: The VM could ping its gateway on eth5, but experienced intermittent connectivity to remote IPs, with about 50% packet loss.
2. Gateway Interface Disabled: The gateway device (Fortigate firewall) interface was disabled.
3. Unexpected Ping Response: Despite the gateway interface being disabled, the VM could still ping the gateway, indicating another device with the same IP address as the gateway.
4. Interface Disabled on VM: eth5 on the VM was disabled, and pinging the gateway IP resulted in timeouts, confirming the conflict was via eth5.
5. ARP Table Check: The ARP table on the VM showed a different MAC address for the gateway IP than the Fortigate device.
6. Port-Mirroring Identified: The VMware team identified that port-mirroring on eth5 was causing the IP conflict.
7. Port-Mirroring Disabled: Disabling port-mirroring on the VSwitch resolved the issue, and the system returned to normal.

Recommendations to Fix the Problem

1. Disable Port-Mirroring: Ensure that port-mirroring is disabled on interfaces where it is not required.
2. Verify Network Configurations: Regularly review and verify network configurations to prevent misconfigurations.
3. Monitor for IP Conflicts: Implement monitoring tools to detect and alert on IP conflicts.
4. Document Network Changes: Maintain detailed documentation of network changes and configurations to facilitate troubleshooting.

Steps Taken to Resolve the Problem

1. Identified the Issue: Analyzed the system logs and identified the presence of martian packets.
2. Disabled Gateway Interface: Temporarily disabled the gateway interface to test for IP conflicts.
3. Disabled VM Interface: Disabled eth5 on the VM to isolate the source of the conflict.
4. Checked ARP Table: Verified the ARP table to identify discrepancies in MAC addresses.
5. Disabled Port-Mirroring: Disabled port-mirroring on the VSwitch, which resolved the IP conflict and restored normal network operation.

Recommendations to Prevent Recurrence

1. Regular Network Audits: Conduct regular audits of network configurations to identify and rectify potential issues.
2. Training for Network Teams: Provide training for network teams on best practices for network configuration and management.
3. Implement Network Monitoring: Use network monitoring tools to detect and alert on unusual network activity, such as IP conflicts and martian packets.
4. Change Management Procedures: Establish and follow strict change management procedures to ensure all network changes are reviewed and documented.

By following these recommendations, similar issues can be prevented in the future, ensuring a stable and reliable network environment.