diff --git a/docker/coturn/alpine/Dockerfile b/docker/coturn/alpine/Dockerfile
index ac06a36..05f0e4d 100644
--- a/docker/coturn/alpine/Dockerfile
+++ b/docker/coturn/alpine/Dockerfile
@@ -109,6 +109,9 @@ RUN apk update \
         libpq mariadb-connector-c sqlite-libs \
         hiredis \
         mongo-c-driver \
+ # Install `dig` tool for `detect-external-ip.sh`.
+ && apk add --no-cache \
+        bind-tools \
  # Cleanup unnecessary stuff.
  && rm -rf /var/cache/apk/*
 
diff --git a/docker/coturn/alpine/rootfs/usr/local/bin/detect-external-ip.sh b/docker/coturn/alpine/rootfs/usr/local/bin/detect-external-ip.sh
index b4e4c57..49bdc8d 100644
--- a/docker/coturn/alpine/rootfs/usr/local/bin/detect-external-ip.sh
+++ b/docker/coturn/alpine/rootfs/usr/local/bin/detect-external-ip.sh
@@ -1,7 +1,115 @@
-#!/bin/sh
+#!/usr/bin/env sh
+# shellcheck shell=dash
 
-if [ -z "$REAL_EXTERNAL_IP" ]; then
-  export REAL_EXTERNAL_IP="$(curl -4 https://icanhazip.com 2>/dev/null)"
+#/ Use DNS to find out about the external IP of the running system.
+#/
+#/ This script is useful when running from a machine that sits behind a NAT.
+#/ Due to how NAT works, machines behind it belong to an internal or private
+#/ subnet, with a different address space than the external or public side.
+#/
+#/ Typically it is possible to make an HTTP request to a number of providers
+#/ that offer the external IP in their response body (eg: ifconfig.me). However,
+#/ why do a slow and heavy HTTP request, when DNS exists and is much faster?
+#/ Well established providers such as OpenDNS or Google offer special hostnames
+#/ that, when resolved, will actually return the IP address of the caller.
+#/
+#/ https://unix.stackexchange.com/questions/22615/how-can-i-get-my-external-ip-address-in-a-shell-script/81699#81699
+#/
+#/
+#/ Arguments
+#/ ---------
+#/
+#/ --ipv4
+#/
+#/   Find the external IPv4 address.
+#/   Optional. Default: Enabled.
+#/
+#/ --ipv6
+#/
+#/   Find the external IPv6 address.
+#/   Optional. Default: Disabled.
+
+
+
+# Shell setup
+# ===========
+
+# Shell options for strict error checking.
+for OPTION in errexit errtrace pipefail nounset; do
+    set -o | grep -wq "$OPTION" && set -o "$OPTION"
+done
+
+# Trace all commands (to stderr).
+#set -o xtrace
+
+
+
+# Shortcut: REAL_EXTERNAL_IP
+# ==========================
+
+if [ -n "${REAL_EXTERNAL_IP:-}" ]; then
+    echo "$REAL_EXTERNAL_IP"
+    exit 0
 fi
 
-exec echo "$REAL_EXTERNAL_IP"
+
+
+# Parse call arguments
+# ====================
+
+CFG_IPV4="true"
+
+while [ $# -gt 0 ]; do
+    case "${1-}" in
+        --ipv4) CFG_IPV4="true" ;;
+        --ipv6) CFG_IPV4="false" ;;
+        *)
+            echo "Invalid argument: '${1-}'" >&2
+            exit 1
+            ;;
+    esac
+    shift
+done
+
+
+
+# Discover the external IP address
+# ================================
+
+if [ "$CFG_IPV4" = "true" ]; then
+    COMMANDS='dig @resolver1.opendns.com myip.opendns.com A -4 +short
+        dig @ns1.google.com o-o.myaddr.l.google.com TXT -4 +short | tr -d \"
+        dig @1.1.1.1 whoami.cloudflare TXT CH -4 +short | tr -d \"
+        dig @ns1-1.akamaitech.net whoami.akamai.net A -4 +short'
+
+    is_valid_ip() {
+        # Check if the input looks like an IPv4 address.
+        # Doesn't check if the actual values are valid; assumes they are.
+        echo "$1" | grep -Eq '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
+    }
+else
+    COMMANDS='dig @resolver1.opendns.com myip.opendns.com AAAA -6 +short
+        dig @ns1.google.com o-o.myaddr.l.google.com TXT -6 +short | tr -d \"
+        dig @2606:4700:4700::1111 whoami.cloudflare TXT CH -6 +short | tr -d \"'
+
+    is_valid_ip() {
+        # Check if the input looks like an IPv6 address.
+        # It's almost impossible to check the IPv6 representation because it
+        # varies wildly, so just check that there are at least 2 colons.
+        [ "$(echo "$1" | awk -F':' '{print NF-1}')" -ge 2 ]
+    }
+fi
+
+echo "$COMMANDS" | while read -r COMMAND; do
+    if IP="$(eval "$COMMAND")" && is_valid_ip "$IP"; then
+        echo "$IP"
+        exit 100 # Exits the pipe subshell.
+    fi
+done
+
+if [ $? -eq 100 ]; then
+    exit 0
+else
+    echo "[$0] All providers failed" >&2
+    exit 1
+fi
diff --git a/docker/coturn/debian/Dockerfile b/docker/coturn/debian/Dockerfile
index 7b64b39..0b4eeb0 100644
--- a/docker/coturn/debian/Dockerfile
+++ b/docker/coturn/debian/Dockerfile
@@ -164,6 +164,9 @@ RUN apt-get update \
             libssl1.1 \
             libpq5 libmariadb3 libsqlite3-0 \
             libhiredis0.14 \
+ # Install `dig` tool for `detect-external-ip.sh`.
+ && apt-get install -y --no-install-recommends --no-install-suggests \
+            dnsutils \
  # Cleanup unnecessary stuff.
  && rm -rf /var/lib/apt/lists/*
 
diff --git a/docker/coturn/debian/rootfs/usr/local/bin/detect-external-ip.sh b/docker/coturn/debian/rootfs/usr/local/bin/detect-external-ip.sh
index b4e4c57..49bdc8d 100644
--- a/docker/coturn/debian/rootfs/usr/local/bin/detect-external-ip.sh
+++ b/docker/coturn/debian/rootfs/usr/local/bin/detect-external-ip.sh
@@ -1,7 +1,115 @@
-#!/bin/sh
+#!/usr/bin/env sh
+# shellcheck shell=dash
 
-if [ -z "$REAL_EXTERNAL_IP" ]; then
-  export REAL_EXTERNAL_IP="$(curl -4 https://icanhazip.com 2>/dev/null)"
+#/ Use DNS to find out about the external IP of the running system.
+#/
+#/ This script is useful when running from a machine that sits behind a NAT.
+#/ Due to how NAT works, machines behind it belong to an internal or private
+#/ subnet, with a different address space than the external or public side.
+#/
+#/ Typically it is possible to make an HTTP request to a number of providers
+#/ that offer the external IP in their response body (eg: ifconfig.me). However,
+#/ why do a slow and heavy HTTP request, when DNS exists and is much faster?
+#/ Well established providers such as OpenDNS or Google offer special hostnames
+#/ that, when resolved, will actually return the IP address of the caller.
+#/
+#/ https://unix.stackexchange.com/questions/22615/how-can-i-get-my-external-ip-address-in-a-shell-script/81699#81699
+#/
+#/
+#/ Arguments
+#/ ---------
+#/
+#/ --ipv4
+#/
+#/   Find the external IPv4 address.
+#/   Optional. Default: Enabled.
+#/
+#/ --ipv6
+#/
+#/   Find the external IPv6 address.
+#/   Optional. Default: Disabled.
+
+
+
+# Shell setup
+# ===========
+
+# Shell options for strict error checking.
+for OPTION in errexit errtrace pipefail nounset; do
+    set -o | grep -wq "$OPTION" && set -o "$OPTION"
+done
+
+# Trace all commands (to stderr).
+#set -o xtrace
+
+
+
+# Shortcut: REAL_EXTERNAL_IP
+# ==========================
+
+if [ -n "${REAL_EXTERNAL_IP:-}" ]; then
+    echo "$REAL_EXTERNAL_IP"
+    exit 0
 fi
 
-exec echo "$REAL_EXTERNAL_IP"
+
+
+# Parse call arguments
+# ====================
+
+CFG_IPV4="true"
+
+while [ $# -gt 0 ]; do
+    case "${1-}" in
+        --ipv4) CFG_IPV4="true" ;;
+        --ipv6) CFG_IPV4="false" ;;
+        *)
+            echo "Invalid argument: '${1-}'" >&2
+            exit 1
+            ;;
+    esac
+    shift
+done
+
+
+
+# Discover the external IP address
+# ================================
+
+if [ "$CFG_IPV4" = "true" ]; then
+    COMMANDS='dig @resolver1.opendns.com myip.opendns.com A -4 +short
+        dig @ns1.google.com o-o.myaddr.l.google.com TXT -4 +short | tr -d \"
+        dig @1.1.1.1 whoami.cloudflare TXT CH -4 +short | tr -d \"
+        dig @ns1-1.akamaitech.net whoami.akamai.net A -4 +short'
+
+    is_valid_ip() {
+        # Check if the input looks like an IPv4 address.
+        # Doesn't check if the actual values are valid; assumes they are.
+        echo "$1" | grep -Eq '^([0-9]{1,3}\.){3}[0-9]{1,3}$'
+    }
+else
+    COMMANDS='dig @resolver1.opendns.com myip.opendns.com AAAA -6 +short
+        dig @ns1.google.com o-o.myaddr.l.google.com TXT -6 +short | tr -d \"
+        dig @2606:4700:4700::1111 whoami.cloudflare TXT CH -6 +short | tr -d \"'
+
+    is_valid_ip() {
+        # Check if the input looks like an IPv6 address.
+        # It's almost impossible to check the IPv6 representation because it
+        # varies wildly, so just check that there are at least 2 colons.
+        [ "$(echo "$1" | awk -F':' '{print NF-1}')" -ge 2 ]
+    }
+fi
+
+echo "$COMMANDS" | while read -r COMMAND; do
+    if IP="$(eval "$COMMAND")" && is_valid_ip "$IP"; then
+        echo "$IP"
+        exit 100 # Exits the pipe subshell.
+    fi
+done
+
+if [ $? -eq 100 ]; then
+    exit 0
+else
+    echo "[$0] All providers failed" >&2
+    exit 1
+fi