Why Does Communication Fail Between Two ECSs in the Same VPC or Packet Loss Occur When They Communicate?
Symptom
Two ECSs in the same VPC cannot communicate with each other or there is packet loss when they communicate.
Troubleshooting
The issues here are described in order of how likely they are to occur.
Troubleshoot the issue by ruling out the causes described here, one by one.
Possible Cause |
Solution |
---|---|
Security group rules |
|
Network ACL rules |
|
ECS NIC configuration |
|
Port unreachable |
See Port Unreachable |
Security Group Rules
Check whether the ECS NIC security group allows the outbound and inbound ICMP traffic.
Take the inbound direction as an example. The security group rules must contain at least one of the following rules.
If packets of other protocols are tested, configure the security group rules to allow the corresponding protocol traffic. For example, if UDP packets are tested, check whether the security group allows the inbound UDP traffic.
Network ACL Rules
- Check whether the subnet of the ECS NIC has an associated network ACL.
- Check the network ACL status in the network ACL list.
- Click the network ACL name and configure rules on the Inbound Rules and Outbound Rules tabs to allow the ICMP traffic.
- If the network ACL is disabled, all packets in the inbound and outbound directions are discarded by default. In this case, delete the network ACL or enable the network ACL and allow the ICMP traffic.
ECS NIC Configuration
- Check whether multiple NICs are configured for the ECS. If the ECS has multiple NICs and the EIP is bound to an extension NIC, configure policy-based routing for the ECS. For details, see How Do I Configure Policy-Based Routes for an ECS with Multiple NICs?
- Log in to the ECS and run the following command to check whether the NIC has been created and obtained a private IP address. If there is no NIC information or the private IP address cannot be obtained, contact technical support.
Figure 3 NIC IP address
- If the CPU usage exceeds 80%, the ECS communication may be adversely affected. Run the following command to check whether the CPU usage of the ECS is too high:
- Run the following command to check whether the ECS has any restrictions on security group rules:
- Run the following command to check whether the /etc/hosts.deny file contains the IP addresses that limit communication:
vi /etc/hosts.deny
If the hosts.deny file contains the IP address of another ECS, delete the IP address from the hosts.deny file and save the file.
Port Unreachable
- If a port of the ECS cannot be reached, check whether the security group rules and network ACL rules enable the port.
- On the Linux ECS, run the following command to check whether the ECS listens on the port: If the ECS does not listen on the port, the ECS communication may be adversely affected.
Submitting a Service Ticket
If the problem persists, submit a service ticket.
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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