To determine if port 5060 (commonly used for SIP services) is open and listening on your CentOS system:

# Check if port is listening locally
ss -tulnp | grep 5060
# Alternative using netstat
netstat -tulnp | grep 5060

To verify if the port is accessible externally:

# From another machine on the same network:
telnet your_server_ip 5060
nc -zv your_server_ip 5060
# If you need to install netcat:
yum install nc -y

To confirm your server has a public IP and isn't behind NAT:

# Check your public IP
curl ifconfig.me
curl icanhazip.com
# Compare with local IP
ip addr show

For CentOS 7/8 firewall management:

# Check firewall status
systemctl status firewalld
# View open ports
firewall-cmd --list-ports
# Add port 5060 if needed
firewall-cmd --permanent --add-port=5060/udp
firewall-cmd --permanent --add-port=5060/tcp
firewall-cmd --reload

For comprehensive testing:

# Install nmap for port scanning
yum install nmap -y
# Scan your own server
nmap -sU -sT -p 5060 localhost
# External testing (from another machine)
nmap -sU -sT -p 5060 your_public_ip

For SIP protocol verification:

# Install sipp for SIP testing
yum install sipp -y
# Basic SIP test (from another machine)
sipp -sn uac your_server_ip:5060

To check if your ISP is blocking the port:

# Test from outside your network
# Use online port checking services like:
# https://www.yougetsignal.com/tools/open-ports/
# https://portchecker.co/

To determine if port 5060 (commonly used for SIP services) is open and listening on your CentOS system, you can use several command-line tools:

# Check if port is listening locally
sudo netstat -tulnp | grep 5060

# Alternative using ss command
sudo ss -tulnp | grep 5060

# Check with nmap (install via yum install nmap)
nmap -sT -p 5060 localhost

Local checks don't guarantee external accessibility. To test from outside:

# On remote machine test connection (replace with your server IP)
telnet your.server.ip 5060
nc -zv your.server.ip 5060

To verify if your system has a public IP and proper routing:

# Check your public IP
curl ifconfig.me
curl icanhazip.com

# Compare with local interface IPs
ip addr show
ip route show

Examine iptables/nftables rules that might block SIP traffic:

# Check current firewall rules
sudo iptables -L -n -v | grep 5060
sudo nft list ruleset | grep 5060

# For firewalld
sudo firewall-cmd --list-all | grep 5060

Here's a comprehensive bash script to test SIP port configuration:

#!/bin/bash

PORT=5060
EXT_IP=$(curl -s ifconfig.me)

echo "=== SIP Port (5060) Connectivity Test ==="
echo "Public IP: $EXT_IP"

echo -e "\n[1] Checking local listeners..."
sudo ss -tulnp | grep $PORT || echo "No local service listening on $PORT"

echo -e "\n[2] Testing external accessibility..."
if which nc &>/dev/null; then
  echo "Testing with netcat from localhost..."
  nc -zv localhost $PORT && echo "Success" || echo "Failed"
  
  echo -e "\nNote: For complete testing, try from external machine:"
  echo "nc -zv $EXT_IP $PORT"
else
  echo "netcat not installed (install with: yum install nc)"
fi

echo -e "\n[3] Checking firewall rules..."
if which iptables &>/dev/null; then
  echo "IPTables rules for $PORT:"
  sudo iptables -L -n -v | grep $PORT || echo "No specific rules found"
fi

if which firewall-cmd &>/dev/null; then
  echo -e "\nFirewalld configuration:"
  sudo firewall-cmd --list-ports | grep $PORT && echo "Port $PORT is open" || \
  echo "Port $PORT not explicitly opened in firewalld"
fi

For more thorough testing, consider these approaches:

• Use tcpdump to monitor SIP traffic: sudo tcpdump -i any port 5060 -vv
• Test with SIPp (SIP testing tool): sipp -sn uac remote_ip:5060
• Check NAT traversal if behind a gateway: stunclient stun.server.com