diff --git a/net/netdev.go b/net/netdev.go
index 1c777d29..35480cbf 100644
--- a/net/netdev.go
+++ b/net/netdev.go
@@ -1,54 +1,20 @@
 package net
 
 import (
+	"encoding/json"
 	"fmt"
 	"net"
 	"os"
-	"regexp"
 	"strconv"
-	"strings"
 
 	"github.com/vishvananda/netlink"
 	"github.com/vishvananda/netns"
 )
 
-var netdevRegExp = regexp.MustCompile(`^([^ ]+?) ([^ ]+?) \[([^]]*)\]$`)
-
 type Dev struct {
-	Name  string
-	MAC   net.HardwareAddr
-	CIDRs []*net.IPNet
-}
-
-func (d Dev) String() string {
-	return fmt.Sprintf("%s %s %s", d.Name, d.MAC, d.CIDRs)
-}
-
-func ParseNetDev(netdev string) (Dev, error) {
-	match := netdevRegExp.FindStringSubmatch(netdev)
-	if match == nil {
-		return Dev{}, fmt.Errorf("invalid netdev: %s", netdev)
-	}
-
-	iface := match[1]
-	mac, err := net.ParseMAC(match[2])
-	if err != nil {
-		return Dev{}, fmt.Errorf("cannot parse mac %s: %s", match[2], err)
-	}
-
-	var cidrs []*net.IPNet
-	for _, cidr := range strings.Split(match[3], " ") {
-		if cidr != "" {
-			ip, ipnet, err := net.ParseCIDR(cidr)
-			if err != nil {
-				return Dev{}, fmt.Errorf("cannot parse cidr %s: %s", cidr, err)
-			}
-			ipnet.IP = ip
-			cidrs = append(cidrs, ipnet)
-		}
-	}
-
-	return Dev{Name: iface, MAC: mac, CIDRs: cidrs}, nil
+	Name  string           `json:"Name,omitempty"`
+	MAC   net.HardwareAddr `json:"MAC,omitempty"`
+	CIDRs []*net.IPNet     `json:"CIDRs,omitempty"`
 }
 
 func LinkToNetDev(link netlink.Link) (Dev, error) {
@@ -125,26 +91,17 @@ func GetNetDevsByVethPeerIds(processID int, peerIDs []int) ([]Dev, error) {
 	}
 
 	var netdevs []Dev
-
 	peersStr := make([]string, len(peerIDs))
 	for i, id := range peerIDs {
 		peersStr[i] = strconv.Itoa(id)
 	}
-	netdevsStr, err := WithNetNSByPid(processID, "list-netdevs", strings.Join(peersStr, ","))
+	nds, err := WithNetNSByPid(processID, "list-netdevs", peersStr...)
 	if err != nil {
 		return nil, fmt.Errorf("list-netdevs failed: %s", err)
 	}
-	for _, netdevStr := range strings.Split(netdevsStr, "\n") {
-		if netdevStr != "" {
-			netdev, err := ParseNetDev(netdevStr)
-			if err != nil {
-				return nil, fmt.Errorf("cannot parse netdev %s: %s", netdevStr, err)
-			}
-			netdevs = append(netdevs, netdev)
-		}
-	}
+	err = json.Unmarshal(nds, &netdevs)
 
-	return netdevs, nil
+	return netdevs, err
 }
 
 // Get the weave bridge interface.
diff --git a/net/netns.go b/net/netns.go
index 5e9e205f..f3a8816a 100644
--- a/net/netns.go
+++ b/net/netns.go
@@ -59,7 +59,7 @@ func WithNetNSLinkUnsafe(ns netns.NsHandle, ifName string, work func(link netlin
 
 // A safe version of WithNetNS* which creates a process executing
 // "nsenter --net=<ns-path> weaveutil <cmd> [args]".
-func WithNetNS(nsPath string, cmd string, args ...string) (string, error) {
+func WithNetNS(nsPath string, cmd string, args ...string) ([]byte, error) {
 	var stdout, stderr bytes.Buffer
 
 	args = append([]string{"--net=" + nsPath, "weaveutil", cmd}, args...)
@@ -67,13 +67,13 @@ func WithNetNS(nsPath string, cmd string, args ...string) (string, error) {
 	c.Stdout = &stdout
 	c.Stderr = &stderr
 	if err := c.Run(); err != nil {
-		return "", fmt.Errorf("%s: %s", string(stderr.Bytes()), err)
+		return nil, fmt.Errorf("%s: %s", string(stderr.Bytes()), err)
 	}
 
-	return string(stdout.Bytes()), nil
+	return stdout.Bytes(), nil
 }
 
-func WithNetNSByPid(pid int, cmd string, args ...string) (string, error) {
+func WithNetNSByPid(pid int, cmd string, args ...string) ([]byte, error) {
 	return WithNetNS(NSPathByPid(pid), cmd, args...)
 }
 
diff --git a/prog/weaveutil/netdev.go b/prog/weaveutil/netdev.go
index a2f29fb0..d35e395b 100644
--- a/prog/weaveutil/netdev.go
+++ b/prog/weaveutil/netdev.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"strconv"
 	"strings"
@@ -97,12 +98,12 @@ func configureARP(args []string) error {
 // listNetDevs outputs network ifaces identified by the given indexes
 // in the format of weavenet.Dev.
 func listNetDevs(args []string) error {
-	if len(args) != 1 {
-		cmdUsage("list-netdevs", "<iface-index>[,<iface-index>]")
+	if len(args) == 0 {
+		cmdUsage("list-netdevs", "<iface-index>[ <iface-index>]")
 	}
 
 	indexes := make(map[int]struct{})
-	for _, index := range strings.Split(args[0], ",") {
+	for _, index := range args {
 		if index != "" {
 			id, err := strconv.Atoi(index)
 			if err != nil {
@@ -117,15 +118,23 @@ func listNetDevs(args []string) error {
 		return err
 	}
 
+	var netdevs []weavenet.Dev
+
 	for _, link := range links {
 		if _, found := indexes[link.Attrs().Index]; found {
 			netdev, err := weavenet.LinkToNetDev(link)
 			if err != nil {
 				return err
 			}
-			fmt.Println(netdev)
+			netdevs = append(netdevs, netdev)
 		}
 	}
 
+	nds, err := json.Marshal(netdevs)
+	if err != nil {
+		return err
+	}
+	fmt.Println(string(nds))
+
 	return nil
 }