diff --git a/README.md b/README.md
index 4edb234..fd17ea8 100644
--- a/README.md
+++ b/README.md
@@ -7,13 +7,14 @@ Sends a DHCPv6-PD solicit message and displays the response (no request is done)
 ````
 testdhcpv6pd [options] [interface name or index]
 
-    available options:
-    -a string
-            anonymize ip addresses (format = list nibble indexes to show) (default "12345678")
-    -l int
-            prefix length (default 64)
-    -s	dont print debug messages
-    -v	display version
+Available options:
+  -a string
+    	anonymize ip addresses (format = list word indexes to show) (default "12345678")
+  -p string
+    	ask for a specific prefix and/or length (default "::/64")
+  -s	dont print debug messages
+  -v	display version
+
 ````
 Without argument, `testdhcpv6pd` will display the available interfaces
 
@@ -21,8 +22,11 @@ Use `-s` to suppress packet debugging
 
 Use `-a format` to anonymize the prefix where format is a list of indexes. Each index, from 1 to 8, is the part number of the address to keep. For instance `-a "18"` only keeps the first and last part of the address.
 
+Use `-p ::/60` to request a /60 prefix or even `-p 2a01:xxx:xxxx:xxxx::/64,` to request a specific prefix
+
 ### notes
 Not tested on *bsd, plan9
 
 Linux systems require *at least* `cap_net_bind_service` capability to bind to port 546 (see `man 7 capabilities`) or just use `sudo`
+
 Darwin/MacOS: use `sudo`
\ No newline at end of file
diff --git a/main.go b/main.go
index 4c94203..286be23 100644
--- a/main.go
+++ b/main.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"log"
 	"net"
+	"net/netip"
 	"os"
 	"strconv"
 	"time"
@@ -55,10 +56,10 @@ func parseInterface(name string) (*net.Interface, error) {
 }
 
 var (
-	optPrefixLength = flag.Int("l", 64, "prefix length")
-	optNoDebug      = flag.Bool("s", false, "dont print debug messages")
-	optVersion      = flag.Bool("v", false, "display version")
-	optAnonymize    = flag.String("a", utils.FormatV6Full, "anonymize ip addresses (format = list word indexes to show)")
+	optNoDebug   = flag.Bool("s", false, "dont print debug messages")
+	optVersion   = flag.Bool("v", false, "display version")
+	optAnonymize = flag.String("a", utils.FormatV6Full, "anonymize ip addresses (format = list word indexes to show)")
+	optPrefix    = flag.String("p", "::/64", "ask for a specific prefix and/or length")
 )
 
 func main() {
@@ -69,9 +70,6 @@ func main() {
 		fmt.Println("version", version)
 		os.Exit(0)
 	}
-	if *optPrefixLength < 1 || *optPrefixLength > 128 {
-		log.Fatal("prefix length")
-	}
 	if len(flag.Args()) != 1 {
 		fmt.Printf("Usage: %s [options] [interface name] or [interface index]\n", os.Args[0])
 		displayInterfaces()
@@ -80,6 +78,10 @@ func main() {
 		os.Exit(0)
 	}
 
+	prefix, err := netip.ParsePrefix(*optPrefix)
+	if err != nil {
+		log.Fatal(err)
+	}
 	iface, err := parseInterface(flag.Args()[0])
 	if err != nil {
 		log.Fatal(err)
@@ -116,8 +118,8 @@ func main() {
 			PreferredLifetime: 0,
 			ValidLifetime:     0,
 			Prefix: &net.IPNet{
-				Mask: net.CIDRMask(*optPrefixLength, 128),
-				IP:   net.IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+				Mask: net.CIDRMask(prefix.Bits(), 128),
+				IP:   prefix.Addr().AsSlice(),
 			},
 			Options: dhcpv6.PrefixOptions{Options: dhcpv6.Options{}},
 		},