Why Do 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.
The ecs01 can ping ecs02 through a private IP address successfully, but ecs02 cannot ping ecs01 through a private IP address.
Troubleshooting
- Ping ecs01 from ecs02 through the EIP. If ecs01 can be pinged, the NIC of ecs01 is working properly.
- Run the arp -n command on ecs02 to check whether the command output contains the MAC address of ecs01. If the command output does not contain the MAC address of ecs01, ecs02 fails to learn the MAC address of ecs01 when using the private IP address to ping ecs01.
- Run the ip a command on ecs01 to check the NIC configuration of ecs01. The following figure shows an example.
Figure 1 Viewing ecs01 NIC configuration
The IP address 192.168.1.40/32 should not be configured based on the command output. As a result, ecs01 fails to send packets to ecs02.
Procedure
Modify the NIC configuration of 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
Connectivity FAQs
- Does a VPN Allow Communication Between Two VPCs?
- Why Are Internet or Internal Domain Names in the Cloud Inaccessible Through Domain Names When My ECS Has Multiple NICs?
- What Are the Priorities of the Custom Route and EIP If Both Are Configured for an ECS to Enable the ECS to Access the Internet?
- Why Are There Intermittent Interruptions When a Local Host Accesses a Website Built on an ECS?
- Why Do ECSs Using Private IP Addresses in the Same Subnet Only Support One-Way Communication?
- Why Does Communication Fail Between Two ECSs in the Same VPC or Packet Loss Occur When They Communicate?
- Why Can't My ECS Use Cloud-init?
- Why Can't My ECS Access the Internet Even After an EIP Is Bound?
- Why Is My ECS Unable to Communicate at a Layer 2 or Layer 3 Network?
- How Do I Handle a BMS Network Failure?
- Why Does My ECS Fail to Obtain an IP Address?
- How Do I Handle a VPN or Direct Connect Connection Network Failure?
- Why Can My Server Be Accessed from the Internet But Cannot Access the Internet?
- Why Can't I Access Websites Using IPv6 Addresses After IPv4/IPv6 Dual Stack Is Configured?
- Why Does My ECS Fail to Communicate with Other After It Has Firewall Installed?
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