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Add probe_icmp_reply_hop_limit (#694)
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IPv6 hop limit (IPv4 TTL) tells how many remaining hops the reply
datagram has. When the target uses a well known initial hop limit,
it can be used to count the number of hops from the target to the
prober and detect routing problems.

Signed-off-by: Luiz Angelo Daros de Luca <[email protected]>
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@luizluca
luizluca committed Oct 8, 2020
1 parent 10b04fc commit 953d80b
Showing 1 changed file with 99 additions and 84 deletions.
183 changes: 99 additions & 84 deletions prober/icmp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -65,14 +65,21 @@ func getICMPSequence() uint16 {

func ProbeICMP(ctx context.Context, target string, module config.Module, registry *prometheus.Registry, logger log.Logger) (success bool) {
var (
socket net.PacketConn
requestType icmp.Type
replyType icmp.Type
requestType icmp.Type
replyType icmp.Type
icmpConn *icmp.PacketConn
v4RawConn *ipv4.RawConn
hopLimitFlagSet bool = true

durationGaugeVec = prometheus.NewGaugeVec(prometheus.GaugeOpts{
Name: "probe_icmp_duration_seconds",
Help: "Duration of icmp request by phase",
}, []string{"phase"})

hopLimitGauge = prometheus.NewGauge(prometheus.GaugeOpts{
Name: "probe_icmp_reply_hop_limit",
Help: "Replied packet hop limit (TTL for ipv4)",
})
)

for _, lv := range []string{"resolve", "setup", "rtt"} {
Expand All @@ -81,7 +88,8 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr

registry.MustRegister(durationGaugeVec)

ip, lookupTime, err := chooseProtocol(ctx, module.ICMP.IPProtocol, module.ICMP.IPProtocolFallback, target, registry, logger)
dstIPAddr, lookupTime, err := chooseProtocol(ctx, module.ICMP.IPProtocol, module.ICMP.IPProtocolFallback, target, registry, logger)

if err != nil {
level.Warn(logger).Log("msg", "Error resolving address", "err", err)
return false
Expand All @@ -104,15 +112,14 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
// Unprivileged sockets are supported on Darwin and Linux only.
tryUnprivileged := runtime.GOOS == "darwin" || runtime.GOOS == "linux"

if ip.IP.To4() == nil {
if dstIPAddr.IP.To4() == nil {
requestType = ipv6.ICMPTypeEchoRequest
replyType = ipv6.ICMPTypeEchoReply

if srcIP == nil {
srcIP = net.ParseIP("::")
}

var icmpConn *icmp.PacketConn
if tryUnprivileged {
// "udp" here means unprivileged -- not the protocol "udp".
icmpConn, err = icmp.ListenPacket("udp6", srcIP.String())
Expand All @@ -130,8 +137,12 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
return
}
}
defer icmpConn.Close()

socket = icmpConn
if err := icmpConn.IPv6PacketConn().SetControlMessage(ipv6.FlagHopLimit, true); err != nil {
level.Debug(logger).Log("msg", "Failed to set Control Message for retrieving Hop Limit", "err", err)
hopLimitFlagSet = false
}
} else {
requestType = ipv4.ICMPTypeEcho
replyType = ipv4.ICMPTypeEchoReply
Expand All @@ -143,21 +154,25 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
if module.ICMP.DontFragment {
// If the user has set the don't fragment option we cannot use unprivileged
// sockets as it is not possible to set IP header level options.
icmpConn, err := net.ListenPacket("ip4:icmp", srcIP.String())
netConn, err := net.ListenPacket("ip4:icmp", srcIP.String())
if err != nil {
level.Error(logger).Log("msg", "Error listening to socket", "err", err)
return
}
defer netConn.Close()

rc, err := ipv4.NewRawConn(icmpConn)
v4RawConn, err = ipv4.NewRawConn(netConn)
if err != nil {
level.Error(logger).Log("msg", "Error creating raw connection", "err", err)
return
}
socket = &v4Conn{c: rc, df: true}
} else {
var icmpConn *icmp.PacketConn
defer v4RawConn.Close()

if err := v4RawConn.SetControlMessage(ipv4.FlagTTL, true); err != nil {
level.Debug(logger).Log("msg", "Failed to set Control Message for retrieving TTL", "err", err)
hopLimitFlagSet = false
}
} else {
if tryUnprivileged {
icmpConn, err = icmp.ListenPacket("udp4", srcIP.String())
if err != nil {
Expand All @@ -174,16 +189,18 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
return
}
}
defer icmpConn.Close()

socket = icmpConn
if err := icmpConn.IPv4PacketConn().SetControlMessage(ipv4.FlagTTL, true); err != nil {
level.Debug(logger).Log("msg", "Failed to set Control Message for retrieving TTL", "err", err)
hopLimitFlagSet = false
}
}
}

defer socket.Close()

var dst net.Addr = ip
var dst net.Addr = dstIPAddr
if !privileged {
dst = &net.UDPAddr{IP: ip.IP, Zone: ip.Zone}
dst = &net.UDPAddr{IP: dstIPAddr.IP, Zone: dstIPAddr.Zone}
}

var data []byte
Expand Down Expand Up @@ -215,7 +232,26 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
durationGaugeVec.WithLabelValues("setup").Add(time.Since(setupStart).Seconds())
level.Info(logger).Log("msg", "Writing out packet")
rttStart := time.Now()
if _, err = socket.WriteTo(wb, dst); err != nil {

if icmpConn != nil {
_, err = icmpConn.WriteTo(wb, dst)
} else {
// Only for IPv4 raw. Needed for setting DontFragment flag.
header := &ipv4.Header{
Version: ipv4.Version,
Len: ipv4.HeaderLen,
Protocol: 1,
TotalLen: ipv4.HeaderLen + len(wb),
TTL: 64,
Dst: dstIPAddr.IP,
Src: srcIP,
}

header.Flags |= ipv4.DontFragment

err = v4RawConn.WriteTo(header, wb, nil)
}
if err != nil {
level.Warn(logger).Log("msg", "Error writing to socket", "err", err)
return
}
Expand Down Expand Up @@ -243,13 +279,52 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr

rb := make([]byte, 65536)
deadline, _ := ctx.Deadline()
if err := socket.SetReadDeadline(deadline); err != nil {
if icmpConn != nil {
err = icmpConn.SetReadDeadline(deadline)
} else {
err = v4RawConn.SetReadDeadline(deadline)
}
if err != nil {
level.Error(logger).Log("msg", "Error setting socket deadline", "err", err)
return
}
level.Info(logger).Log("msg", "Waiting for reply packets")
for {
n, peer, err := socket.ReadFrom(rb)
var n int
var peer net.Addr
var err error
var hopLimit float64 = -1

if dstIPAddr.IP.To4() == nil {
var cm *ipv6.ControlMessage
n, cm, peer, err = icmpConn.IPv6PacketConn().ReadFrom(rb)
// HopLimit == 0 is valid for IPv6, although go initialize it as 0.
if cm != nil && hopLimitFlagSet {
hopLimit = float64(cm.HopLimit)
} else {
level.Debug(logger).Log("msg", "Cannot get Hop Limit from the received packet. 'probe_icmp_reply_hop_limit' will be missing.")
}
} else {
var cm *ipv4.ControlMessage
if icmpConn != nil {
n, cm, peer, err = icmpConn.IPv4PacketConn().ReadFrom(rb)
} else {
var h *ipv4.Header
var p []byte
h, p, cm, err = v4RawConn.ReadFrom(rb)
if err == nil {
copy(rb, p)
n = len(p)
peer = &net.IPAddr{IP: h.Src}
}
}
if cm != nil && hopLimitFlagSet {
// Not really Hop Limit, but it is in practice.
hopLimit = float64(cm.TTL)
} else {
level.Debug(logger).Log("msg", "Cannot get TTL from the received packet. 'probe_icmp_reply_hop_limit' will be missing.")
}
}
if err != nil {
if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
level.Warn(logger).Log("msg", "Timeout reading from socket", "err", err)
Expand All @@ -274,72 +349,12 @@ func ProbeICMP(ctx context.Context, target string, module config.Module, registr
}
if bytes.Equal(rb[:n], wb) {
durationGaugeVec.WithLabelValues("rtt").Add(time.Since(rttStart).Seconds())
if hopLimit >= 0 {
hopLimitGauge.Set(hopLimit)
registry.MustRegister(hopLimitGauge)
}
level.Info(logger).Log("msg", "Found matching reply packet")
return true
}
}
}

type v4Conn struct {
c *ipv4.RawConn

df bool
src net.IP
}

func (c *v4Conn) ReadFrom(b []byte) (int, net.Addr, error) {
h, p, _, err := c.c.ReadFrom(b)
if err != nil {
return 0, nil, err
}

copy(b, p)
n := len(b)
if len(p) < len(b) {
n = len(p)
}
return n, &net.IPAddr{IP: h.Src}, nil
}

func (d *v4Conn) WriteTo(b []byte, addr net.Addr) (int, error) {
ipAddr, err := net.ResolveIPAddr(addr.Network(), addr.String())
if err != nil {
return 0, err
}

header := &ipv4.Header{
Version: ipv4.Version,
Len: ipv4.HeaderLen,
Protocol: 1,
TotalLen: ipv4.HeaderLen + len(b),
TTL: 64,
Dst: ipAddr.IP,
Src: d.src,
}

if d.df {
header.Flags |= ipv4.DontFragment
}

return len(b), d.c.WriteTo(header, b, nil)
}

func (d *v4Conn) Close() error {
return d.c.Close()
}

func (d *v4Conn) LocalAddr() net.Addr {
return nil
}

func (d *v4Conn) SetDeadline(t time.Time) error {
return d.c.SetDeadline(t)
}

func (d *v4Conn) SetReadDeadline(t time.Time) error {
return d.c.SetReadDeadline(t)
}

func (d *v4Conn) SetWriteDeadline(t time.Time) error {
return d.c.SetWriteDeadline(t)
}

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