diff --git a/Dynv6.ps1 b/Dynv6.ps1
index 2c48721..46a577c 100644
--- a/Dynv6.ps1
+++ b/Dynv6.ps1
@@ -53,17 +53,21 @@
 # IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ###################
 
-
+# we need zone and token, we also accept, netmask, and overrides
 param(
     [string] $zone = $(throw "-zone is required"),
     [string] $token = $(throw "-token is required"),
     [string] $netmask = "128",
-    [string] $logfile = "$env:USERPROFILE\\.dynv6.log"
+    [string] $logfile = "$env:USERPROFILE\\.dynv6.log",
+    [string] $ipv4 = $null,
+    [string] $ipv6 = $null
 )
 
+# we store ip addresses in files, so we only update when there is a change
 $file4 = "$env:USERPROFILE\\.dynv6.addr4"
 $file6 = "$env:USERPROFILE\\.dynv6.addr6"
 
+# load existing ip addresses, when available
 if (Test-Path -Path $file4) {
     $old4 = Get-Content -Path $file4
 } else {
@@ -83,32 +87,47 @@ $update6 = [System.Uri]'https://dynv6.com/api/update'
 
 Get-Date | Tee-Object -FilePath $logfile -Append | Out-Host
 
-$current4 = Invoke-RestMethod -Method Get -Uri $lookup4
-$current6 = Invoke-RestMethod -Method Get -Uri $lookup6
+# lookup IPv4, will be skipped if variable already set
+if ($ipv4 -eq $null) {
+    $ipv4 = Invoke-RestMethod -Method Get -Uri $lookup4
+}
 
-if ($old4 -eq $current4) {
+# lookup IPv6, will be skipped if variable already set
+if ($ipv6 -eq $null) {
+    $ipv6 = Invoke-RestMethod -Method Get -Uri $lookup6
+}
+
+# update IPv4, if changed
+if ($old4 -eq $ipv4) {
     Tee-Object -FilePath $logfile -Append -InputObject "IPv4 address unchanged" | Out-Host
 } else {
+    # send IPv4 address to dynv6
     Tee-Object -FilePath $logfile -Append -InputObject "Updating IPv4" | Out-Host
     $body = @{
        zone = $zone
        token = $token
-       ipv4 = $current4
+       ipv4 = $ipv4
     }
     Invoke-RestMethod -Method Get -Uri $update4 -Body $body | Tee-Object -FilePath $logfile -Append | Out-Host
-    Out-File -FilePath $file4 -InputObject $current4
+
+    # save current IPv4 address
+    Out-File -FilePath $file4 -InputObject $ipv4
 }
 
-if ($old6 -eq $current6) {
+# update IPv6, if changed
+if ($old6 -eq $ipv6) {
     Tee-Object -FilePath $logfile -Append -InputObject "IPv6 address unchanged" | Out-Host
 } else {
+    # send IPv6 address to dynv6
     Tee-Object -FilePath $logfile -Append -InputObject "Updating IPv6" | Out-Host
     $body = @{
        zone = $zone
        token = $token
-       ipv6 = "$current6/$netmask"
+       ipv6 = "$ipv6/$netmask"
     }
     Invoke-RestMethod -Method Get -Uri $update6 -Body $body | Tee-Object -FilePath $logfile -Append | Out-Host
-    Out-File -FilePath $file6 -InputObject $current6
+
+    # save current IPv6 address
+    Out-File -FilePath $file6 -InputObject $ipv6
 }
 
diff --git a/dynv6.sh b/dynv6.sh
index 2f5d3bd..9988a89 100755
--- a/dynv6.sh
+++ b/dynv6.sh
@@ -1,21 +1,24 @@
 #!/bin/sh
 
+# we need zone and token, we also accept, netmask, and overrides
 zone=$1
 device=$2
 scope=$3
 
+# stop if we do not have the required information
+if [ -z "$zone" -o -z "$token" ]; then
+    echo "Usage: token=<your-authentication-token> [netmask=64] [ipv4=<override>] [ipv6=<override>] $0 your-name.dynv6.net [device] [scope]"
+    exit 1
+fi
+
+# we store ip addresses in files, so we only update when there is a change
 file4="$HOME/.dynv6.addr4"
 file6="$HOME/.dynv6.addr6"
 
+# load existing ip addresses, when available
 [ -e $file4 ] && old4=`cat $file4`
 [ -e $file6 ] && old6=`cat $file6`
 
-# ensure we have required information
-if [ -z "$zone" -o -z "$token" ]; then
-    echo "Usage: token=<your-authentication-token> [netmask=64] $0 your-name.dynv6.net [device] [scope]"
-    exit 1
-fi
-
 # [device] would be something like "eth0" or "wlan0"
 if [ -n "$device" ]; then
     device="dev $device"
@@ -45,36 +48,39 @@ else
     lookup4="$bin https://ipinfo.io/ip"
 fi
 
-# lookup IPv4
-ipv4=`$lookup4`
+# lookup IPv4, will be skipped if variable already set
 if [ -z "$ipv4" ]; then
-    echo "failed to lookup IPv4 address, continuing with 'auto'"
-    ipv4="auto"
-fi
-
-# calculate IPv6
-address6=$(ip -6 addr list $scope $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1)
-
-if [ -z "$address6" ]; then
-    echo "no IPv6 address found"
-    exit 1
+    ipv4=`$lookup4`
+    if [ -z "$ipv4" ]; then
+        echo "failed to lookup IPv4 address, continuing with 'auto'"
+        ipv4="auto"
+    fi
 fi
 
 if [ -z "$netmask" ]; then
     netmask="128"
 fi
 
-ipv6="$address6/$netmask"
+# lookup IPv6, will be skipped if variable already set
+if [ -z "$ipv6" ]; then
+    ipv6=$(ip -6 addr list $scope $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1)
+    if [ -z "$ipv6" ]; then
+        echo "no IPv6 address found"
+        exit 1
+    fi
+fi
+ipv6="$ipv6/$netmask"
 
 # update IPv4, if changed
 if [ "$old4" = "$ipv4" ]; then
     echo "IPv4 address unchanged"
 else
+    # send IPv4 address to dynv6
     echo -n "Updating IPv4: "
     $bin "https://dynv6.com/api/update?zone=$zone&ipv4=$ipv4&token=$token"
     echo ""
 
-    # save current address
+    # save current IPv4 address
     echo $ipv4 > $file4
 fi
 
@@ -82,12 +88,12 @@ fi
 if [ "$old6" = "$ipv6" ]; then
     echo "IPv6 address unchanged"
 else
-    # send addresses to dynv6
+    # send IPv6 address to dynv6
     echo -n "Updating IPv6: "
     $bin "https://dynv6.com/api/update?zone=$zone&ipv6=$ipv6&token=$token"
     echo ""
 
-    # save current address
+    # save current IPv6 address
     echo $ipv6 > $file6
 fi