Send ICMP errors when the network is unreachable

Before this change, we would silently drop packets when unable to determine a
route to the destination host. This change brings us into line with RFC 792
(IPv4) and RFC 4443 (IPv6), both of which specify that gateways should return
an ICMP error to the sender when unable to reach the destination.

Startblock:
  has LGTM from asfez
  and then
  add reviewer ghanan
PiperOrigin-RevId: 372214051

1 files changed, 27 insertions, 0 deletions

diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index d8a10065d..d5f941c5f 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -1528,6 +1528,30 @@ type IGMPStats struct {
 	// LINT.ThenChange(network/ipv4/stats.go:multiCounterIGMPStats)
 }
 
+// IPForwardingStats collects stats related to IP forwarding (both v4 and v6).
+type IPForwardingStats struct {
+	// Unrouteable is the number of IP packets received which were dropped
+	// because the netstack could not construct a route to their
+	// destination.
+	Unrouteable *StatCounter
+
+	// ExhaustedTTL is the number of IP packets received which were dropped
+	// because their TTL was exhausted.
+	ExhaustedTTL *StatCounter
+
+	// LinkLocalSource is the number of IP packets which were dropped
+	// because they contained a link-local source address.
+	LinkLocalSource *StatCounter
+
+	// LinkLocalDestination is the number of IP packets which were dropped
+	// because they contained a link-local destination address.
+	LinkLocalDestination *StatCounter
+
+	// Errors is the number of IP packets received which could not be
+	// successfully forwarded.
+	Errors *StatCounter
+}
+
 // IPStats collects IP-specific stats (both v4 and v6).
 type IPStats struct {
 	// LINT.IfChange(IPStats)
@@ -1596,6 +1620,9 @@ type IPStats struct {
 	// OptionUnknownReceived is the number of unknown IP options seen.
 	OptionUnknownReceived *StatCounter
 
+	// Forwarding collects stats related to IP forwarding.
+	Forwarding IPForwardingStats
+
 	// LINT.ThenChange(network/internal/ip/stats.go:MultiCounterIPStats)
 }