IPv6 App Development Guide: Making Applications IPv6-Ready

Most production outages caused by IPv6 are not protocol failures — they are application bugs. A server that binds only to 0.0.0.0, a database column storing IP addresses as INT UNSIGNED, a regex that rejects colons, a rate limiter keyed on a /128 that changes every ten minutes. These are not edge cases. They are the default behavior of code written without considering that IPv6 exists, deployed onto networks where IPv6 is the primary — or only — protocol. As of 2025, over 45% of Google's traffic arrives over IPv6, T-Mobile US runs an IPv6-only network with NAT64 for legacy destinations, and Apple requires IPv6 compatibility for App Store approval. Writing IPv4-only code is writing code that is broken on a large and growing fraction of the internet.

This guide covers the concrete changes needed to make network applications work correctly on IPv6-only, dual-stack, and NAT64 networks — from socket creation to database schemas to load balancer configuration.

Dual-Stack Sockets: AF_INET6 with IPV6_V6ONLY

The most important socket-level concept for IPv6 application development is the dual-stack socket. On most operating systems, an AF_INET6 socket can accept both IPv4 and IPv6 connections when the IPV6_V6ONLY socket option is set to 0. The kernel maps incoming IPv4 connections to IPv4-mapped IPv6 addresses (e.g., ::ffff:192.0.2.1). This means a single socket can serve all clients regardless of protocol version.

# Python: dual-stack server socket
import socket

sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
# IPV6_V6ONLY=0 enables dual-stack (accepts IPv4 and IPv6)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(('::', 8080))  # :: = all interfaces, both protocols
sock.listen(128)

while True:
    conn, addr = sock.accept()
    # addr[0] will be "::ffff:192.0.2.1" for IPv4 clients
    # addr[0] will be "2001:db8::1" for IPv6 clients
    print(f"Connection from {addr[0]} port {addr[1]}")

The behavior of IPV6_V6ONLY defaults varies across operating systems, and this is a constant source of bugs:

Never rely on the default. Always explicitly set IPV6_V6ONLY to the value you need. If you want dual-stack, set it to 0. If you need separate sockets for IPv4 and IPv6 (e.g., for different bind addresses or firewall rules), set it to 1 and create two sockets.

// Go: dual-stack listener using net.Listen
// Go's net package handles dual-stack automatically on Linux.
// On BSD systems, it creates two listeners internally.
ln, err := net.Listen("tcp", ":8080")  // listens on all interfaces, both protocols

// If you need explicit control:
lc := net.ListenConfig{}
ln, err := lc.Listen(ctx, "tcp", "[::]:8080")

There is an important caveat on some BSD-derived systems: if you set IPV6_V6ONLY=0 and bind to ::, you cannot simultaneously bind a separate AF_INET socket to 0.0.0.0 on the same port — the dual-stack socket already claims the IPv4 port. On Linux, this conflict does not occur because the kernel handles the mapping differently. If your application must run on both Linux and BSD, test both paths.

Dual-Stack Socket (IPV6_V6ONLY=0) IPv6 Client 2001:db8::42 AF_INET6 socket IPv4 Client 192.0.2.100 AF_INET socket Kernel Mapping IPv4 src 192.0.2.100 ↓ ::ffff:192.0.2.100 Server Socket AF_INET6, bind(::, 8080) IPV6_V6ONLY=0 peer: 2001:db8::42 peer: ::ffff:192.0.2.100 Single socket serves both protocol versions Native IPv6 IPv4 mapped to ::ffff:x.x.x.x Platform Defaults for IPV6_V6ONLY Linux: 0 (dual-stack)   |   FreeBSD/OpenBSD: 1 (v6-only)   |   Windows: 0   |   macOS: 0

Address Resolution: getaddrinfo Done Right

Hard-coding AF_INET or manually constructing sockaddr_in structures is the single most common cause of IPv6 incompatibility. The correct approach is getaddrinfo(), which resolves hostnames to socket addresses in a protocol-independent way. The key flags control how resolution interacts with the host's actual network connectivity:

# Python: protocol-independent connection
import socket

def connect_to_host(hostname, port):
    """Connect to a host using the best available protocol."""
    hints = socket.getaddrinfo(
        hostname, port,
        family=socket.AF_UNSPEC,       # Accept any protocol
        type=socket.SOCK_STREAM,
        flags=socket.AI_ADDRCONFIG     # Only return usable protocols
    )

    # Try each address in order (Happy Eyeballs would interleave)
    last_err = None
    for family, socktype, proto, canonname, sockaddr in hints:
        try:
            sock = socket.socket(family, socktype, proto)
            sock.settimeout(5.0)
            sock.connect(sockaddr)
            return sock
        except OSError as e:
            last_err = e
            sock.close()
    raise last_err

// Node.js: dns.lookup uses getaddrinfo internally
// Since Node 17+, autoSelectFamily enables Happy Eyeballs (RFC 8305)
const net = require('net');

const socket = net.connect({
  host: 'example.com',
  port: 443,
  autoSelectFamily: true,  // try IPv6 and IPv4 in parallel
});

A critical pitfall with AI_ADDRCONFIG: on a host that has only a loopback IPv6 address (::1) but no global IPv6 address, AI_ADDRCONFIG will suppress AAAA results. This is correct behavior — the host cannot reach IPv6 destinations — but it surprises developers testing in containers or minimal VMs that lack IPv6 configuration. Inside Docker containers, IPv6 is often disabled by default, so AI_ADDRCONFIG correctly returns only IPv4 results even if the host outside the container is dual-stack.

Happy Eyeballs (RFC 8305)

Even with correct getaddrinfo() usage, naively trying addresses sequentially causes poor user experience when one protocol is broken. If a host has both A and AAAA records but IPv6 connectivity is flaky, a sequential approach waits for the IPv6 connection to time out (often 30+ seconds) before falling back to IPv4. TCP connection timeouts are painful.

RFC 8305 (Happy Eyeballs v2) specifies interleaving connection attempts: start an IPv6 connection, then after 250ms without success, start an IPv4 connection in parallel. Use whichever completes first. Most modern standard libraries and HTTP clients implement this:

Storing IP Addresses: Never Use a 32-bit Integer

Storing IPv4 addresses as INT UNSIGNED or uint32 is a pattern that appears in countless codebases and works until the first IPv6 client connects. An IPv6 address is 128 bits — four times the size. You cannot fix this with a bigger integer column; you need a proper representation.

Database Schemas

PostgreSQL provides the best native support with its INET and CIDR types, which store both IPv4 and IPv6 addresses efficiently and support index-based lookups:

-- PostgreSQL: proper IP address storage
CREATE TABLE access_log (
    id          BIGSERIAL PRIMARY KEY,
    client_ip   INET NOT NULL,           -- stores IPv4 or IPv6
    subnet      CIDR,                    -- network prefix with mask
    created_at  TIMESTAMPTZ DEFAULT now()
);

-- Index for fast lookups
CREATE INDEX idx_access_log_ip ON access_log USING gist (client_ip inet_ops);

-- Query: find all requests from a /48
SELECT * FROM access_log
WHERE client_ip << '2001:db8:abcd::/48'::cidr;

-- Query: check if IP is in a known range
SELECT * FROM access_log
WHERE client_ip <<= '192.0.2.0/24'::cidr
   OR client_ip <<= '2001:db8::/32'::cidr;

MySQL/MariaDB lack native IP types. The best approach is VARBINARY(16) with INET6_ATON() / INET6_NTOA():

-- MySQL: use VARBINARY(16) for both IPv4 and IPv6
CREATE TABLE access_log (
    id          BIGINT AUTO_INCREMENT PRIMARY KEY,
    client_ip   VARBINARY(16) NOT NULL,
    created_at  DATETIME DEFAULT CURRENT_TIMESTAMP,
    INDEX idx_ip (client_ip)
);

-- Insert: INET6_ATON handles both IPv4 and IPv6
INSERT INTO access_log (client_ip)
VALUES (INET6_ATON('2001:db8::1')),
       (INET6_ATON('192.0.2.50'));

-- Query
SELECT INET6_NTOA(client_ip) AS ip FROM access_log;

Do not use VARCHAR(45) for IP addresses. While it technically fits the longest IPv6 representation, it wastes space (45 bytes + overhead vs. 16 bytes for VARBINARY), produces inconsistent results due to multiple valid text representations of the same IPv6 address (::1 vs. 0:0:0:0:0:0:0:1), and makes range queries impossible without conversion functions. If you must use a text column, always canonicalize addresses before storage using RFC 5952 rules.

In-Memory Representation

In application code, always use sockaddr_storage (C/C++) or your language's equivalent to hold addresses of either family:

// C: sockaddr_storage holds any address family
#include <sys/socket.h>
#include <netinet/in.h>

struct sockaddr_storage client_addr;
socklen_t addr_len = sizeof(client_addr);
int client_fd = accept(server_fd, (struct sockaddr *)&client_addr, &addr_len);

// Determine family after accept
if (client_addr.ss_family == AF_INET6) {
    struct sockaddr_in6 *addr6 = (struct sockaddr_in6 *)&client_addr;
    // Check for IPv4-mapped address
    if (IN6_IS_ADDR_V4MAPPED(&addr6->sin6_addr)) {
        // This is actually an IPv4 client on a dual-stack socket
    }
} else if (client_addr.ss_family == AF_INET) {
    struct sockaddr_in *addr4 = (struct sockaddr_in *)&client_addr;
}

// Go: net.IP handles both transparently
import "net"

func handleConn(conn net.Conn) {
    addr := conn.RemoteAddr().(*net.TCPAddr)
    ip := addr.IP

    // net.IP is a byte slice: 4 bytes for IPv4, 16 bytes for IPv6
    if ip.To4() != nil {
        // IPv4 (or IPv4-mapped IPv6)
    } else {
        // Native IPv6
    }
}

URL Formatting: Brackets and RFC 5952

IPv6 addresses contain colons, which collide with the port separator in URLs and socket addresses. RFC 3986 specifies that IPv6 literals in URIs must be enclosed in brackets: http://[2001:db8::1]:8080/path. Forgetting the brackets is a common source of parsing failures.

Rules for IPv6 in URLs and configuration:

RFC 5952 defines a canonical text representation for IPv6 addresses. When you log, store, or display IPv6 addresses, always canonicalize them to avoid comparing two representations of the same address and finding them "different":

# Python: canonicalize IPv6 addresses
import ipaddress

# All of these are the same address:
addrs = [
    "2001:0DB8:0000:0000:0000:0000:0000:0001",
    "2001:db8:0:0:0:0:0:1",
    "2001:db8::1",
    "2001:0db8::0001",
]

for a in addrs:
    canonical = str(ipaddress.ip_address(a))
    print(canonical)  # All print: 2001:db8::1

Regex Patterns for IP Addresses

Matching IPv6 addresses with regex is notoriously difficult because of the compression rules (the :: shorthand can appear anywhere and represents a variable number of zero groups). Do not write your own IPv6 regex. Use your language's standard library to parse and validate addresses, and use regex only for quick extraction from unstructured text where you accept some false positives:

# Python: validate with ipaddress module, not regex
import ipaddress

def is_valid_ip(s):
    """Returns True for any valid IPv4 or IPv6 address."""
    try:
        ipaddress.ip_address(s)
        return True
    except ValueError:
        return False

# For extracting IPs from log lines (rough pattern, not a validator):
import re

# This catches most IPv6 addresses in text; not a strict validator
IPV6_ROUGH = r'[0-9a-fA-F:]{2,39}'
IPV4_PATTERN = r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'
IP_PATTERN = rf'(?:{IPV6_ROUGH}|{IPV4_PATTERN})'

# Better: extract candidates with regex, then validate with ipaddress
for match in re.finditer(IP_PATTERN, log_line):
    candidate = match.group()
    try:
        addr = ipaddress.ip_address(candidate)
        # addr is a valid IPv4Address or IPv6Address
    except ValueError:
        pass  # Not a valid IP, skip

If you are parsing structured formats (JSON, HTTP headers, log formats you control), do not use regex at all. Parse the structure first, then validate the IP field with your language's IP address library.

Logging IP Addresses

Log IPv6 addresses in their full canonical (RFC 5952) form. Never truncate them. An IPv6 address can be up to 39 characters, and your log format, log parsing pipeline, and dashboards all need to handle this. Common mistakes:

For dual-stack sockets, when you receive a connection from an IPv4 client, the peer address will be an IPv4-mapped IPv6 address (::ffff:192.0.2.1). Decide on a consistent policy: either always log the raw address (including the ::ffff: prefix) or always strip the mapping and log the underlying IPv4 address. Do not mix both in the same log stream — it makes correlation impossible.

# Python: consistent IP logging for dual-stack sockets
import ipaddress

def normalize_peer_address(raw_addr: str) -> str:
    """Normalize a peer address for consistent logging.

    Strips ::ffff: prefix from IPv4-mapped IPv6 addresses
    so that 192.0.2.1 always appears the same in logs
    regardless of whether the client connected over IPv4 or IPv6.
    """
    try:
        addr = ipaddress.ip_address(raw_addr)
        if isinstance(addr, ipaddress.IPv6Address) and addr.ipv4_mapped:
            return str(addr.ipv4_mapped)  # Returns "192.0.2.1"
        return str(addr)  # Canonical RFC 5952 form
    except ValueError:
        return raw_addr  # Return as-is if unparseable

Rate Limiting and Geolocation with IPv6

Rate limiting by IP address breaks immediately on IPv6 if you key on individual /128 addresses. IPv6 clients routinely use multiple addresses from the same prefix due to privacy extensions (RFC 8981), where the interface identifier (lower 64 bits) is randomized and rotated every few minutes. A single user can generate dozens of different source addresses in an hour. Additionally, IPv6 allocations are large: a typical residential user gets a /56 or /64, and an organization may have a /48.

IPv6 Rate Limiting: Aggregate by Prefix Single User (Privacy Extensions) 2001:db8:abcd:1234:a1b2:c3d4:e5f6:7890 2001:db8:abcd:1234:ff92:17ab:3c4d:8812 2001:db8:abcd:1234:5e3f:9a22:b7c1:4455 ... new address every few minutes Same /64 prefix, rotating interface IDs Prefix: /64 IID: random Rate Limiting Strategy  Per /128 (individual address)  Useless: user rotates past the limit ✗  Per /64 (residential prefix)  Good default for end-user rate limits ✓  Per /48 (organizational prefix)  Use for abuse detection / org-level limits ✓ IPv4: rate limit per /32 (single address)

Recommended rate limiting strategy:

# Python: IPv6-aware rate limiting
import ipaddress
from collections import defaultdict

class RateLimiter:
    """Rate limiter that aggregates IPv6 by /64 prefix."""

    def __init__(self, limit: int, window_seconds: int):
        self.limit = limit
        self.window = window_seconds
        self.counters = defaultdict(list)  # key -> [timestamps]

    def _get_key(self, ip_str: str) -> str:
        addr = ipaddress.ip_address(ip_str)
        if isinstance(addr, ipaddress.IPv6Address):
            if addr.ipv4_mapped:
                # IPv4-mapped: rate limit per IPv4 /32
                return str(addr.ipv4_mapped)
            # IPv6: aggregate to /64
            network = ipaddress.ip_network(
                f"{addr}/64", strict=False
            )
            return str(network.network_address)
        else:
            # IPv4: rate limit per individual address
            return str(addr)

    def is_allowed(self, ip_str: str) -> bool:
        key = self._get_key(ip_str)
        # ... standard sliding window logic on key ...

Geolocation databases face the same issue. MaxMind's GeoIP2 and similar databases include IPv6 ranges, but the granularity is often /48 or /32 for IPv6 versus /24 for IPv4. Accuracy for IPv6 geolocation is generally lower because allocation records are less mature and privacy extensions obscure the specific endpoint. Do not assume the same geolocation precision you get with IPv4.

IPv6 Privacy Extensions and Rotating Addresses

RFC 8981 (formerly RFC 4941) defines temporary addresses that are generated by randomizing the 64-bit interface identifier. Most modern operating systems enable this by default:

This means any system that tracks users by IP address — session binding, abuse detection, audit logging — must account for address rotation. A user's IPv6 address may change mid-session. Session management must use cookies or tokens, not source IP. Audit trails must be correlatable by /64 prefix or by authenticated identity, not by individual address.

Framework Default Bind Behavior

Modern web frameworks differ significantly in their default listening behavior. Knowing the default matters because it determines whether your application is reachable over IPv6 out of the box:

Node.js / Express.js

// Express defaults to all interfaces, dual-stack on Linux
const app = require('express')();
app.listen(3000);  // Binds to 0.0.0.0 — IPv4 only!

// For dual-stack:
app.listen(3000, '::');  // Binds to [::] — IPv4 and IPv6 on Linux

// Or explicitly dual-stack in Node 18+:
const server = app.listen(3000, '::', () => {
    console.log('Listening on [::]:3000 (dual-stack)');
});

Express defaults to 0.0.0.0 (IPv4 only). You must explicitly specify :: to get IPv6 support. This is probably the most common source of "works on my machine but not on IPv6-only networks" bugs in Node.js applications.

Python / Flask / Gunicorn

# Flask development server: IPv4-only by default
app.run(host='0.0.0.0', port=5000)    # IPv4 only
app.run(host='::', port=5000)          # IPv6 + IPv4 (dual-stack on Linux)

# Gunicorn: specify bind address
# gunicorn -b [::]:8000 app:app        # dual-stack
# gunicorn -b 0.0.0.0:8000 -b [::]:8000 app:app  # explicit both

Java / Spring Boot

# application.properties: Spring Boot binds to 0.0.0.0 by default
# For dual-stack, set the JVM flag:
# java -Djava.net.preferIPv6Addresses=true -jar app.jar

# Or in application.properties:
server.address=::
server.port=8080

Java's behavior depends on JVM flags. By default, Java prefers IPv4 on dual-stack systems. Set -Djava.net.preferIPv6Stack=true to use IPv6 sockets, or -Djava.net.preferIPv6Addresses=true to prefer IPv6 addresses in DNS resolution while keeping dual-stack sockets.

ASP.NET / Kestrel

// ASP.NET Kestrel: IPAddress.IPv6Any creates a dual-stack socket
var builder = WebApplication.CreateBuilder(args);
builder.WebHost.ConfigureKestrel(options =>
{
    options.Listen(IPAddress.IPv6Any, 5000);  // [::]:5000 dual-stack
    // or:
    options.ListenAnyIP(5000);  // Binds both IPv4 and IPv6
});

Kestrel's ListenAnyIP() creates both IPv4 and IPv6 listeners automatically, which is the safest default for cross-platform deployment.

Load Balancers and Reverse Proxies

If your application sits behind a reverse proxy (and most production applications do), the proxy must be configured for IPv6 on both the frontend (client-facing) and backend (upstream) sides. The most critical detail is preserving the client's real IP address in a header, since the proxy terminates the TCP connection.

Nginx

# nginx.conf: dual-stack frontend with IPv6 upstream
server {
    listen 80;
    listen [::]:80;           # IPv6 — separate listen directive required
    listen 443 ssl;
    listen [::]:443 ssl;

    # Pass real client IP to backend
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Real-IP $remote_addr;  # may be IPv6

    location / {
        # Upstream can be IPv6 too
        proxy_pass http://[::1]:8080;
    }
}

HAProxy

# haproxy.cfg: dual-stack bind
frontend http_front
    bind :80                    # IPv4 + IPv6 on Linux (dual-stack)
    bind :::80 v4v6             # Explicit: v4v6 keyword for dual-stack

    option forwardfor           # X-Forwarded-For header (IPv4 or IPv6)

backend app_servers
    server app1 [::1]:8080     # IPv6 backend
    server app2 192.0.2.10:8080  # IPv4 backend

When your application parses X-Forwarded-For or X-Real-IP, it must handle IPv6 addresses. These headers may contain bracketed addresses ([2001:db8::1]) or bare addresses (2001:db8::1) depending on the proxy. Parse defensively: strip brackets if present, then validate with your language's IP address library.

Kubernetes Dual-Stack Services

Kubernetes supports dual-stack networking since v1.23 (stable). A dual-stack Service gets both a ClusterIP (IPv4) and a ClusterIP (IPv6), and external LoadBalancer services can expose both protocols. Configuration requires that the cluster was deployed with dual-stack enabled (both an IPv4 and IPv6 pod CIDR and service CIDR).

# Kubernetes: dual-stack Service
apiVersion: v1
kind: Service
metadata:
  name: my-app
spec:
  type: LoadBalancer
  ipFamilyPolicy: PreferDualStack   # or RequireDualStack
  ipFamilies:
    - IPv6
    - IPv4                          # order = preference
  selector:
    app: my-app
  ports:
    - port: 80
      targetPort: 8080

The ipFamilyPolicy field controls behavior:

The ipFamilies array determines which address family is primary. Pod-to-pod communication within a dual-stack cluster uses the pod's IP directly, and pods on dual-stack clusters receive both an IPv4 and IPv6 address. The CNI plugin (Calico, Cilium, etc.) must support dual-stack — not all do.

DNS Considerations

Publishing AAAA records for your service is the final piece of making it reachable over IPv6. Without AAAA records in DNS, no IPv6 client can connect — even if your server is fully dual-stack. Key considerations:

Health Checks and Monitoring

Health check endpoints must be reachable over both IPv4 and IPv6 if your service advertises both. A load balancer that health-checks only over IPv4 will continue routing IPv6 traffic to a backend whose IPv6 stack is broken. Configure separate health checks for each protocol, or ensure the health check uses the same path as client traffic.

Monitor IPv6 traffic ratios. If your service normally sees 30% IPv6 traffic and that suddenly drops to zero, something is broken — likely a DNS issue (AAAA records disappeared) or a network change that broke IPv6 routing. Alert on significant deviations in the IPv4/IPv6 traffic ratio, not just on absolute metrics.

# Prometheus: track connections by IP version
from prometheus_client import Counter
import ipaddress

ipv4_connections = Counter('connections_ipv4_total', 'IPv4 connections')
ipv6_connections = Counter('connections_ipv6_total', 'IPv6 connections')

def track_connection(remote_addr: str):
    addr = ipaddress.ip_address(remote_addr)
    if isinstance(addr, ipaddress.IPv6Address):
        if addr.ipv4_mapped:
            ipv4_connections.inc()
        else:
            ipv6_connections.inc()
    else:
        ipv4_connections.inc()

Configuration Files: Bind Addresses and ACLs

Configuration formats must accommodate IPv6 addresses without ambiguity. The colon problem reappears in configuration files that use colon as a key-value separator, and in ACL rules that need to specify both addresses and prefixes.

# Example: YAML configuration that handles both protocols
server:
  bind:
    - address: "::"        # dual-stack
      port: 8080
    - address: "::1"       # loopback only (IPv6)
      port: 9090

acl:
  allow:
    - "10.0.0.0/8"           # IPv4 private
    - "172.16.0.0/12"        # IPv4 private
    - "192.168.0.0/16"       # IPv4 private
    - "fc00::/7"             # IPv6 ULA (unique local)
    - "2001:db8:abcd::/48"   # specific IPv6 allocation
  deny:
    - "0.0.0.0/0"            # deny all other IPv4
    - "::/0"                 # deny all other IPv6

When implementing ACL matching, always use proper CIDR matching — never string prefix matching. The string 2001:db8:: is a prefix of 2001:db8::1 as text, but 2001:db8:1:: is also within the 2001:db8::/32 network despite not starting with the same string. Use ipaddress.ip_network and the in operator:

# Correct CIDR matching
import ipaddress

allowed_networks = [
    ipaddress.ip_network("10.0.0.0/8"),
    ipaddress.ip_network("fc00::/7"),
    ipaddress.ip_network("2001:db8:abcd::/48"),
]

def is_allowed(ip_str: str) -> bool:
    addr = ipaddress.ip_address(ip_str)
    return any(addr in net for net in allowed_networks)

Testing on IPv6-Only Networks

The hardest bugs to catch are those that only appear on IPv6-only networks. On a dual-stack network, your application may silently fall back to IPv4 for every connection, masking IPv6 bugs entirely. Mobile carriers increasingly deploy IPv6-only with NAT64 and 464XLAT for IPv4 compatibility, so these environments are not hypothetical. Set up a test environment that forces IPv6:

Automated CI/CD pipelines should include IPv6-only test runs. GitHub Actions runners are dual-stack, so you can create an IPv6-only container within the runner to execute tests.

Common Pitfalls Reference

A summary of the most frequent IPv6 application bugs, each of which has been observed in production systems:

Each of these is fixable with straightforward code changes. The difficulty is not technical — it is ensuring that IPv6 is tested as a first-class path, not an afterthought. Use the BGP looking glass to verify that your network's IPv6 prefixes are visible in the global routing table, and check your deployment against each item in this list. The transition to IPv6 is well underway, and applications that do not handle it correctly will fail for a growing fraction of their users.

See BGP routing data in real time

Open Looking Glass
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