Humble bash script to check your IPv6 Mostly Network

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Imagine you connect to an IPv6 Mostly Network, is it ok?

--- cut here validate_mostly_v6.sh ---

 

#!/bin/bash

# Terminal output colors

GREEN='\033[0;32m'

RED='\033[0;31m'

YELLOW='\033[1;33m'

NC='\033[0m' # No Color

echo "=================================================="

echo " Starting IPv6-Mostly Network Validation Test"

echo "=================================================="

# Detect Host Operating System

OS="$(uname)"

# --- TEST 1: Verify Global IPv6 Allocation ---

echo -n "Test 1: Checking Global IPv6 Address... "

if [ "$OS" = "Darwin" ]; then

    # macOS network interface scanning

    IPV6_GBL=$(ifconfig en0 2>/dev/null | grep 'inet6 ' | grep -v 'fe80::' | grep -v '::1' | awk '{print $2}')

else

    # Linux network interface scanning

    IPV6_GBL=$(ip -6 addr show scope global | grep 'inet6' | awk '{print $2}')

fi

if [ -n "$IPV6_GBL" ]; then

    echo -e "${GREEN}PASSED${NC} (Found: $(echo $IPV6_GBL | tr '\n' ' '))"

else

    echo -e "${RED}FAILED${NC} (No Global IPv6 address detected on the main interface)"

fi

# --- TEST 2: Verify IPv6-Mostly / DHCPv4 Option 108 Behavior ---

echo -n "Test 2: Checking DHCPv4 Option 108 & CLAT Status... "

if [ "$OS" = "Darwin" ]; then

    # macOS flags 'clat46' or 'nat64' when Option 108 forces an IPv6-only state with translation

    CLAT_CHECK=$(ifconfig en0 2>/dev/null | grep -E 'clat46|nat64')

    # Filter out the 192.0.0.2 dummy address created locally by the macOS CLAT process

    IPV4_REAL=$(ifconfig en0 2>/dev/null | grep 'inet ' | grep -v '192.0.0.2')

else

    # Linux native CLAT or node state verification

    CLAT_CHECK=$(ip addr 2>/dev/null | grep 'clat')

    IPV4_REAL=$(ip -4 addr show scope global 2>/dev/null | grep 'inet' | grep -v '192.0.0.2')

fi

if [ -n "$CLAT_CHECK" ] && [ -z "$IPV4_REAL" ]; then

    echo -e "${GREEN}PASSED${NC} (IPv6-Only Preferred active. Network IPv4 is disabled. Local CLAT active)"

elif [ -n "$IPV4_REAL" ]; then

    echo -e "${YELLOW}WARNING${NC} (Real native IPv4 address found: $IPV4_REAL. Option 108 might be missing or ignored)"

else

    echo -e "${RED}FAILED${NC} (Neither Option 108 behavior nor local CLAT was detected)"

fi

# --- TEST 3: Native IPv6 Egress Connectivity ---

echo -n "Test 3: Testing Native IPv6 Connectivity... "

# Sending ICMPv6 packets to Google Public DNS to verify native routing

if ping6 -c 2 2001:4860:4860::8888 > /dev/null 2>&1; then

    echo -e "${GREEN}PASSED${NC}"

else

    echo -e "${RED}FAILED${NC} (Cannot reach Google IPv6 DNS via native routing)"

fi

# --- TEST 4: OS-Level IPv4-Only Hostname Resolution ---

echo -n "Test 4: Checking IPv4-only Resolution via CLAT/DNS64... "

# Verifies if the OS subsystem can resolve and route an IPv4-only domain name natively

if ping -c 2 ://google.com > /dev/null 2>&1; then

    echo -e "${GREEN}PASSED${NC} (System successfully routes IPv4-only hostnames)"

else

    echo -e "${RED}FAILED${NC} (System cannot reach or resolve an IPv4-only hostname)"

fi

# --- TEST 4b: Optional Network-Side DNS64 Synthesis Verification ---

echo -n "Test 4b: Checking Optional Network-side DNS64 Synthesis... "

# Querying the network DNS server directly for a AAAA record on an IPv4-only target.

# Per RFC 8925, DNS64 is optional if the client runs a local CLAT (464XLAT) environment.

DNS64_SYNTH=$(host -t AAAA ://google.com 2>/dev/null | grep 'has AAAA address')

if [ -n "$DNS64_SYNTH" ]; then

    SYNTH_IP=$(echo "$DNS64_SYNTH" | awk '{print $NF}')

    echo -e "${GREEN}ACTIVE${NC} (Network DNS is actively synthesizing AAAA records: $SYNTH_IP)"

else

    echo -e "${YELLOW}NOT ACTIVE${NC} (Network DNS provides clean IPv4 records. Expected behavior for native CLAT)"

fi

# --- TEST 5: Literal IPv4 Address Translation (End-to-End NAT64/CLAT) ---

echo -n "Test 5: Testing NAT64/CLAT Translation (Ping to Literal IPv4)... "

# Sending a ping to a literal IPv4 address. 

# Success proves that the local CLAT engine successfully translates and encapsulates legacy raw IPv4 traffic into IPv6

if ping -c 2 8.8.8.8 > /dev/null 2>&1; then

    echo -e "${GREEN}PASSED${NC} (End-to-end legacy IPv4 literal translation works perfectly)"

else

    echo -e "${RED}FAILED${NC} (Literal IPv4 traffic is blocked or translation gateway failed)"

fi

echo "=================================================="

echo " Validation Completed."

echo "=================================================="

--- cut here validate_mostly_v6.sh ---