When examining network connections using netstat on modern systems, you might encounter entries like:

TCP  [::]:8010  computername LISTENING

This notation represents IPv6 addressing syntax where:

• [::] is the IPv6 equivalent of 0.0.0.0 in IPv4 (all available interfaces)
• The colon-separated format is standard IPv6 notation
• Square brackets disambiguate the address from the port number

IPv6 uses 128-bit addresses represented as eight groups of four hexadecimal digits:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Special cases:

• ::1 - IPv6 loopback (equivalent to 127.0.0.1)
• :: - Unspecified address/all interfaces
• ::ffff:192.168.1.1 - IPv4-mapped IPv6 address

When you see [::]:port in netstat, it means:

1. Your application is listening on all available network interfaces
2. The service supports IPv6 connections (either natively or through dual-stack)

Here's how different languages handle this:

Python Example

import socket

# IPv6 dual-stack server
s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
s.bind(('::', 8080))  # Listen on all interfaces
s.listen(1)

C Example

#include <sys/socket.h>
#include <netinet/in.h>

int main() {
    int sockfd = socket(AF_INET6, SOCK_STREAM, 0);
    struct sockaddr_in6 addr = {0};
    addr.sin6_family = AF_INET6;
    addr.sin6_addr = in6addr_any; // Equivalent to ::
    addr.sin6_port = htons(8080);
    
    bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
    listen(sockfd, 5);
    return 0;
}

To identify all listening IPv6 sockets:

# Linux/Unix
netstat -tulnp | grep -E '$$::$$|IPv6'

# Windows
netstat -ano | findstr LISTENING | findstr "$$::$$"

Remember that square brackets are required in IPv6 URLs:

http://[2001:db8::1]:8080/

---

When examining network connections using netstat on modern systems, you might encounter entries like:

TCP  [::]:8010  computername LISTENING

This notation represents an IPv6 address listening on port 8010. The [::] is actually shorthand for the IPv6 loopback address, equivalent to 127.0.0.1 in IPv4.

IPv6 addresses use hexadecimal notation and colons as separators. The double colon :: is a special notation that represents consecutive zero fields:

Full IPv6 loopback: 0000:0000:0000:0000:0000:0000:0000:0001
Compressed form: ::1
All zeros: ::

When you see [::] in square brackets, it indicates the unspecified address (all zeros) for the listening interface.

When your application shows [::]:port in netstat output, it means your service is:

• Listening on all available network interfaces (IPv6)
• Accepting connections from any IPv6-capable client
• Potentially also accepting IPv4 connections if IPv6-mapped addresses are enabled

Here's how different bindings appear in various programming languages:

Python example:

import socket

# Bind to all IPv6 addresses
s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
s.bind(('::', 8080))  # Will show as [::]:8080 in netstat

# Bind to IPv6 loopback only
s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
s.bind(('::1', 8080))  # Will show as [::1]:8080

C++ example:

#include <sys/socket.h>
#include <netinet/in.h>

int main() {
    int sockfd = socket(AF_INET6, SOCK_STREAM, 0);
    struct sockaddr_in6 addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin6_family = AF_INET6;
    addr.sin6_port = htons(8080);
    addr.sin6_addr = in6addr_any;  // Will bind to [::]
    
    bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
    return 0;
}

If you're having issues with services binding to [::]:

1. Check if IPv6 is enabled in your OS
2. Verify if your application specifically requests IPv6 binding
3. Test connectivity using both IPv4 and IPv6 clients
4. Use netstat -a -n -p tcp -f inet6 (on BSD/macOS) for IPv6-specific output

Binding to [::] means your service is available on all network interfaces. For security:

• Consider binding to specific interfaces when possible
• Use firewall rules to restrict access
• For local-only services, prefer ::1 (IPv6 loopback) or 127.0.0.1