From 10f774db9235f6b633c713687faa6e569da1f523 Mon Sep 17 00:00:00 2001
From: Kyle Carberry <kyle@carberry.com>
Date: Tue, 9 May 2023 17:27:21 +0000
Subject: [PATCH] wgengine/netstack: switch to cubic congestion control

See https://github.com/tailscale/tailscale/pull/8106
---
 wgengine/netstack/netstack.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/wgengine/netstack/netstack.go b/wgengine/netstack/netstack.go
index 6161fa422bcf7..ec6a4a1c6e4ca 100644
--- a/wgengine/netstack/netstack.go
+++ b/wgengine/netstack/netstack.go
@@ -179,6 +179,11 @@ func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magi
 	if tcpipErr != nil {
 		return nil, fmt.Errorf("could not enable TCP SACK: %v", tcpipErr)
 	}
+	congestionOpt := tcpip.CongestionControlOption("cubic") // Reno is used by default
+	tcpipErr = ipstack.SetTransportProtocolOption(tcp.ProtocolNumber, &congestionOpt)
+	if tcpipErr != nil {
+		return nil, fmt.Errorf("could not set TCP congestion control: %v", tcpipErr)
+	}
 	linkEP := &protectedLinkEndpoint{Endpoint: channel.New(512, tstun.DefaultMTU(), "")}
 	if tcpipProblem := ipstack.CreateNIC(nicID, linkEP); tcpipProblem != nil {
 		return nil, fmt.Errorf("could not create netstack NIC: %v", tcpipProblem)