When troubleshooting network issues where you can connect to a server using Telnet but cannot ping it, it indicates specific network configurations or restrictions. Here’s a systematic guide to analyze and resolve the problem:

• Ping uses the ICMP (Internet Control Message Protocol) to test network connectivity. A failed ping suggests ICMP packets are being blocked.

• Telnet works on the TCP protocol for connecting to specific ports. A successful Telnet connection indicates the TCP port is open and the service is reachable.

For details, please refer to https://github.com/Nirvan-Pandey/OCI_DOC/wiki/28_Telnet_VS_Ping

• ICMP Blocked: Network devices (firewalls, routers) might block ICMP packets.

• Host Configuration: The server’s operating system might be configured to drop ICMP requests.

• Network Path Issues: ICMP packets might be dropped at intermediate hops due to security policies.

• Telnet Allowed: The TCP port for the Telnet connection is open, which indicates that application traffic is permitted.

telnet <server_ip> <port>

Telnet Connection is working.

ping <server_ip>

Both instances are not able to ping each other.

Ingress Rule

There is no rule defined for ping(ICMP) to reach to each other.

Egress Rule

• Navigate Menu-->Networking-->Click on vcn-->Copy IPV4(series) of the public subnet

• Allow this copied public subnet by adding Ingress rule under Security list.

Networking-->Virtual Cloud Networks-->VCN-->Security List Details-->Ingress Rule-->Add

Choose Source Type- CIDR, Source CIDR-- Copied public ip series IP Protocol --ICMP

• Ping got successful, hence the servers are able to reach one another, within the subnet.