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fix: set TCPMaxRetries to 5 for reasonable timeouts on send #61

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Merged
merged 1 commit into from
Sep 20, 2024
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fix: set TCPMaxRetries to 5 for reasonable timeouts on send #61

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16 changes: 16 additions & 0 deletions wgengine/netstack/netstack.go
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,17 @@ const (
// CUBIC congestion control is the default in Windows, Linux, and MacOS, and generally achieves
// better throughput on large, long networks.
congestionControlCubic = "cubic"
// maxRetries is the maximum number of retransmissions that the TCP stack should undertake for
// unacked TCP segments, that is, when we are trying to send TCP data and the other side is
// unresponsive. It does not affect TCP operation while both sides are idle. The retry timeout
// has a minimum of 200ms and maximum of 120s, and grows exponentially when the other side is
// unresponsive. The default maxRetries in gVisor is 15, which means in practice over ten
// minutes of unresponsiveness before we time out. Setting to 5 should time out in 15-30s,
// depending on the latency of the connection. In Coder's system we depend on Wireguard as the
// underlay, which retries handshakes on a 5s timer, so we don't want to shorten the timeout
// less than 15s or so, to give us several chances to re-establish a Wireguard session after
// idling.
maxRetries = 5
)

// Create creates and populates a new Impl.
Expand Down Expand Up @@ -227,6 +238,11 @@ func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magi
if tcpipErr != nil {
return nil, fmt.Errorf("could not set congestion control: %v", tcpipErr)
}
retries := tcpip.TCPMaxRetriesOption(maxRetries)
tcpipErr = ipstack.SetTransportProtocolOption(tcp.ProtocolNumber, &retries)
if tcpipErr != nil {
return nil, fmt.Errorf("could not set max retries: %v", tcpipErr)
}

linkEP := NewEndpoint(512, tstun.DefaultMTU(), "")
if tcpipProblem := ipstack.CreateNIC(nicID, linkEP); tcpipProblem != nil {
Expand Down
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