diff options
| author | Ghanan Gowripalan <ghanan@google.com> | 2021-01-27 19:06:47 -0800 |
|---|---|---|
| committer | gVisor bot <gvisor-bot@google.com> | 2021-01-27 19:08:51 -0800 |
| commit | b85b23e50d1c264ff4821e182ad89a8ea3d0e0c5 (patch) | |
| tree | 9180366b5d4106e048b41fd1d34a436be6719d0f /pkg/tcpip/transport | |
| parent | 1d22284c13cc040e52c2130386c10d8f84f6bbd6 (diff) | |
Confirm neighbor reachability with TCP ACKs
As per RFC 4861 section 7.3.1,
A neighbor is considered reachable if the node has recently received
a confirmation that packets sent recently to the neighbor were
received by its IP layer. Positive confirmation can be gathered in
two ways: hints from upper-layer protocols that indicate a connection
is making "forward progress", or receipt of a Neighbor Advertisement
message that is a response to a Neighbor Solicitation message.
This change adds support for TCP to let the IP/link layers know that a
neighbor is reachable.
Test: integration_test.TestTCPConfirmNeighborReachability
PiperOrigin-RevId: 354222833
Diffstat (limited to 'pkg/tcpip/transport')
| -rw-r--r-- | pkg/tcpip/transport/tcp/connect.go | 8 | ||||
| -rw-r--r-- | pkg/tcpip/transport/tcp/snd.go | 11 |
2 files changed, 19 insertions, 0 deletions
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go index 62954d7e4..6df4e6525 100644 --- a/pkg/tcpip/transport/tcp/connect.go +++ b/pkg/tcpip/transport/tcp/connect.go @@ -1335,6 +1335,14 @@ func (e *endpoint) protocolMainLoop(handshake bool, wakerInitDone chan<- struct{ } } + // Reaching this point means that we successfully completed the 3-way + // handshake with our peer. + // + // Completing the 3-way handshake is an indication that the route is valid + // and the remote is reachable as the only way we can complete a handshake + // is if our SYN reached the remote and their ACK reached us. + e.route.ConfirmReachable() + drained := e.drainDone != nil if drained { close(e.drainDone) diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go index 28ef9f899..027c2a4a8 100644 --- a/pkg/tcpip/transport/tcp/snd.go +++ b/pkg/tcpip/transport/tcp/snd.go @@ -1390,6 +1390,17 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) { acked := s.sndUna.Size(ack) s.sndUna = ack + // The remote ACK-ing at least 1 byte is an indication that we have a + // full-duplex connection to the remote as the only way we will receive an + // ACK is if the remote received data that we previously sent. + // + // As of writing, linux seems to only confirm a route as reachable when + // forward progress is made which is indicated by an ACK that removes data + // from the retransmit queue. + if acked > 0 { + s.ep.route.ConfirmReachable() + } + ackLeft := acked originalOutstanding := s.outstanding for ackLeft > 0 { |