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What Do I Do If ECSs Using Private IP Addresses in the Same Subnet Only Support One-Way Communication?

Symptom

Two ECSs (ecs01 and ecs02) are in the same subnet in a VPC. Their IP addresses are 192.168.1.141 and 192.168.1.40, respectively.

The ECS ecs02 private IP address can be pinged from ECS ecs01, but ECS ecs01 private IP address cannot be pinged from ECS ecs02.

Fault Locating

  1. Ping ECS ecs01 from ECS ecs02 through the EIP. If ECS ecs01 can be pinged, the NIC of ECS ecs01 is working properly.
  2. Run the arp -n command on ECS ecs02 to check whether the command output contains the MAC address of ECS ecs01. If the command output does not contain the MAC address of ECS ecs01, the ECS ecs02 fails to learn the ECS ecs01 MAC address when using the private IP address to ping ECS ecs01.
  3. Run the ip a command on ecs01 to check the NIC configuration of ECS ecs01. The following figure shows an example.
    Figure 1 Viewing ECS ecs01 NIC configuration

    The IP address 192.168.1.40/32 should not be configured based on the command output. As a result, ECS ecs01 fails to send packets to ECS ecs02.

Troubleshooting Procedure

Modify the NIC configuration of ECS ecs01. Run the following command to delete the redundant IP address, for example, 192.168.1.40/32, configured on the NIC eth0:

ip a del 192.168.1.40/32 dev eth0

Parent topic: Connectivity