General: Forums subtopic: App & System Services > Networking TN3151 Choosing the right networking API Networking Overview document — Despite the fact that this is in the archive, this is still really useful. TLS for App Developers forums post Choosing a Network Debugging Tool documentation WWDC 2019 Session 712 Advances in Networking, Part 1 — This explains the concept of constrained networking, which is Apple’s preferred solution to questions like How do I check whether I’m on Wi-Fi? TN3135 Low-level networking on watchOS TN3179 Understanding local network privacy Adapt to changing network conditions tech talk TCP and UDP ports used by Apple software products support article Understanding Also-Ran Connections forums post Extra-ordinary Networking forums post Foundation networking: Forums tags: Foundation, CFNetwork URL Loading System documentation — NSURLSession, or URLSession in Swift, is the recommended API for HTTP[S] on Apple platforms. Moving to Fewer, Larger Transfers forums post Testing Background Session Code forums post Network framework: Forums tag: Network Network framework documentation — Network framework is the recommended API for TCP, UDP, and QUIC on Apple platforms. Building a custom peer-to-peer protocol sample code (aka TicTacToe) Implementing netcat with Network Framework sample code (aka nwcat) Configuring a Wi-Fi accessory to join a network sample code Moving from Multipeer Connectivity to Network Framework forums post NWEndpoint History and Advice forums post Wi-Fi (general): How to modernize your captive network developer news post Wi-Fi Fundamentals forums post Filing a Wi-Fi Bug Report forums post Working with a Wi-Fi Accessory forums post — This is part of the Extra-ordinary Networking series. Wi-Fi (iOS): TN3111 iOS Wi-Fi API overview technote Wi-Fi Aware framework documentation WirelessInsights framework documentation iOS Network Signal Strength forums post Network Extension Resources Wi-Fi on macOS: Forums tag: Core WLAN Core WLAN framework documentation Secure networking: Forums tags: Security Apple Platform Security support document Preventing Insecure Network Connections documentation — This is all about App Transport Security (ATS). WWDC 2017 Session 701 Your Apps and Evolving Network Security Standards [1] — This is generally interesting, but the section starting at 17:40 is, AFAIK, the best information from Apple about how certificate revocation works on modern systems. WWDC 2025 Session 314 Get ahead with quantum-secure cryptography Available trusted root certificates for Apple operating systems support article Requirements for trusted certificates in iOS 13 and macOS 10.15 support article About upcoming limits on trusted certificates support article Apple’s Certificate Transparency policy support article What’s new for enterprise in iOS 18 support article — This discusses new key usage requirements. Prepare your network environment for stricter security requirements support article — This is primarily of interest to folks developing management software, for example, an MDM server. Technote 2232 HTTPS Server Trust Evaluation Technote 2326 Creating Certificates for TLS Testing QA1948 HTTPS and Test Servers Miscellaneous: More network-related forums tags: 5G, QUIC, Bonjour On FTP forums post Using the Multicast Networking Additional Capability forums post Investigating Network Latency Problems forums post Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] This video is no longer available from Apple, but the URL should help you locate other sources of this info.

Hi all, I’m developing a watchOS app that uses a WebSocket API to process voice audio. However, I keep encountering this error when trying to establish the connection: nw_endpoint_flow_failed_with_error [C1 <server URL>:443 failed parent-flow (unsatisfied (Path was denied by NECP policy), interface: ipsec2, ipv4, ipv6, proxy)] already failing, returning I’ve read Technical Note TN3135, which outlines an exception for audio streaming apps. My app is an audio streaming app, and I’ve already added background audio mode to the app’s capabilities. However, I’m not sure what else is required to meet the exception described in TN3135. Questions How do I meet the exception outlined in TN3135 for WebSocket audio streaming on watchOS? Does NECP enforce additional restrictions even with background audio enabled, and how can I address this? Any guidance or examples of implementing WebSocket audio streaming on watchOS would be greatly appreciated. Thanks!

I want to know the right way/API/usage to use NWConnectionGroup to send both datagram and non-datagram stream. I am currently working on an P2P video streaming app. I want to leverage NWConnectionGroup over QUIC to handle both message channel (traditionally handled by a TCP connection) and media channel (traditionally handled by sth. over UDP) to transmit SRT packets back and forth. I created a NWConnectionGroup and it worked fine on non-datagram parts. The problems are with datagram part. I tried extracting a connection with datagram = true either from the group or from message, doesn't and in some cases it breaks other non-datagram connections. I currently send datagram directly using the NWConnectionGroup.send(content:completion). It kinda works but I keep seeing it canceled a lot of messages, which breaks SRT shortly after start. The warnings belong flooded my console. (Seems like want me to create a connection to transmit datagram, how?) nw_connection_create_with_connection [C1600] Original connection not yet connected nw_connection_group_create_connection_for_endpoint_and_parameters [G1] failed to create connection with parameters quic, local: fe80::439:68b4:6ec2:694%en0.60517, definite, attribution: developer, server I must use it in wrong way. What should I do to fix it?

Many times the device totally lost connectivity, WIFI is completely down, no ip was assigned after device wakeup. From system log I can see BPF socket for DHCP was closed and detached right after attached to en0 in DHCP INIT phase, as result even the DHCP server sent back OFFER(I see server sent OFFER back from packet capture), but there is no persistent BPF socket since it is closed reception during the entire INIT phase. It is definitely an OS issue, is it a known issue? Please help understand Why BPF socket was close right after sending DISCOVER? Default 0x0 0 0 kernel: bpf26 attached to en0 by configd:331 2026-03-25 14:06:33.625851+0100 0x31dea Default 0x0 0 0 kernel: bpf26 closed and detached from en0 fcount 0 dcount 0 by configd:331 System log and packet capture attach, please check.

I've been investigating memory consumption issues with a network extension. It seems as though the "leak" exists within the network extension framework. Looking at a memory graph, there appears to be a _socketFlows dictionary or similar in the network extension framework that holds all of the flows and they continue to pile up and consume memory. The problem seems to be particularly bad when I leave my MacBook plugged in and running over the weekend and come back on Monday. For instance, in that time period, the memory consumption grew from <100MB to >1GB. To try to narrow this down to see if it was an "us" problem or truly in the framework, I installed Objective-See Foundation's Lulu tool, which also uses a network extension. It similarly saw memory grow from around 30MB or less to 600MB in the same time frame. Has anyone else seen this? We do have an open feedback ticket FB18731867 that might be related that has to do with seeing multiple instances of the same data filter provider started and maybe running in a network extension.

I’m using Apple’s Network framework to implement a UDP client using NWConnection, and I have a question regarding the lifecycle of the DispatchQueue associated with an NWConnection instance. Let's assume I have an NWConnection instance, and I associate it with a dispatch queue using the start(queue:) API, such that network OS events for the NWConnection instance can be delivered to this queue. My understanding is that this association would result in NWConnection holding a strong reference to the DispatchQueue object. Now, I perform some I/O (send/receive) on the NWConnection instance and immediately perform the following steps. Also, assume that the completion closures for those I/O operations do not capture or otherwise retain the NWConnection. Call connection.cancel() and then release my last strong reference to the NWConnection. Without waiting for the connection to transition to the .cancelled state, I also release my last strong reference to the associated DispatchQueue. My question is: Does NWConnection, during its teardown, retain the DispatchQueue until the cancellation completions for all pending I/O operations associated with the connection have been delivered/executed, given that the application no longer holds any strong references to either the NWConnection or the DispatchQueue? Or, once cancel() is called, does NWConnection immediately release its reference to the DispatchQueue, in which case whether the pending callbacks are ultimately executed depends on whether the application has kept the queue alive?

We are having an issue with the Local Network permission pop-up not getting triggered for our apps that need to communicate with devices via local network interfaces/addresses. As we understand, apps using UDP should trigger this, causing macOS to prompt for access, or, if denied, fail to connect. However, we are facing issues with macOS not prompting this popup at all. Here are important and related points: Our application is packaged as a .app package and distributed independently (not on the App Store). The application controls hardware that we manufacture. In order to find the hardware on the network, we send a UDP broadcast with a message for our hardware on the local network, and the hardware responds with a message back. However, the popup (to ask for permission) never shows up. The application is not able to find the hardware device. It is interesting to note that data is still sent out to the network (without the popup) but we receive back the wrong data. The behaviour is consistent macOS Sequoia (and above) with both Apple And Intel silicon. Workarounds that have been tried: Manual Authorization: One solution suggested in various blogs was to go to "Settings → Privacy and Security-> Local network", find your application and grant access. However, the application never shows up in the list here. Firewall: No difference is seen in behaviour with firewall being ON OR OFF. Setting NSLocalNetworkUsageDescription: We have also tried setting the Info.plist adding the NSLocalNetworkUsageDescription with a meaningful string and updating the NSBonjourServices. Running Via terminal (WORKS): Running the application via terminal sees no issues. The application runs correctly and is able to send UDP and receive correct data (and find the devices on the network). But this is not an appropriate solution. How can we get this bug/issue fixed in macOS Sequoia (and above)? Are there any other solutions/workarounds that we can try on our end?

We maintain a large file-sync app. After our upload endpoint moved to HTTP/2, we found that when multiple NSURLSessionUploadTasks run concurrently, all tasks send their request headers immediately (multiplexed on a single connection — confirmed identical localPort via URLSessionTaskMetrics), but request bodies are transmitted essentially one task at a time: while one task's body saturates the uplink, the other tasks send zero body bytes for the entire duration (countOfBytesSent == 0). This reproduces with both background sessions (BackgroundUploadTask) and default sessions (LocalUploadTask), on Wi-Fi and cellular. iOS 26.5, Xcode 26.3, tasks created with uploadTask(with:fromFile:), multipart POST. This becomes a hard failure behind a load balancer with slow-POST (RUDY) protection: requests whose first body KB doesn't arrive within 5s are rejected with 408. The starved tasks fail even though the network is healthy. For comparison, OkHttp on Android writes bodies in interleaved 16KB DATA frames under identical conditions, so all streams pass the first-KB check. Metrics excerpt (4 concurrent uploads, one h2 connection): task 1: duration 18.7s, sent 180MB (full line rate) task 2: duration 22.8s, sent 43MB (transmitted only after task 1 finished) task 3: duration 46.0s, sent 247MB (after task 2) task 4: duration 5.2s, sent 0 bytes → 408 from the gateway In one run a starved stream sent exactly 65,536 bytes (the default initial stream window) and then stalled. Questions: Is this sender-side scheduling (no round-robin between streams' DATA frames) the expected CFNetwork behavior? Does URLSessionTask.priority influence HTTP/2 stream weighting for upload bodies? Is there any other way to influence bandwidth sharing between concurrent uploads? Is there any supported way to opt out of HTTP/2 (constrain ALPN to HTTP/1.1) or cap concurrent streams per connection from the client side? We believe there isn't, but would like to confirm. What is the recommended pattern for concurrent large uploads in this situation? Filed as FB24062619 with full sanitized metrics attached. Happy to provide more data.

model : iphone 17 ios version: 26.2 app used: https://developer.apple.com/documentation/wifiaware/building-peer-to-peer-apps Here is our observation when we tried to make wifi aware connection between iphone and our wifi device. note : we used iphone as subscriber ( view simulation) 1.pairing & bootstrapping was successfully done 2.Data path was successfully established between iphone and our device. after data path establishment ,within few seconds , DATA PATH TERMINATION was sent from iphone which leads to pairing verification with new NMI address. Same behaviour is noticed even when we try to establish connection between two iphone devices. Here we have few questions. Once we establish data path , Why iphone initiates data path termination instead using the same service for data path exchange. 2.Why do we go for PAIRING VERIFICATION everytime.

We have an iOS app (Alamofire 5.9+, backed by URLSession) that talks to a LAN dashcam: HTTP/1.1 TLS 1.2 The device runs an embedded C HTTPS server Responses commonly include Connection: close (a new TCP connection is opened for each request) From Wireshark, looking at Client Hello, we observe: First connection: full handshake; a Session ID is negotiated Next new TCP connection: Client Hello carries that Session ID and completes an abbreviated handshake (resumption succeeds) After that: the same Session ID is not reused again Questions we want to confirm For TLS 1.2 Session ID resumption (RFC 5246), does iOS / URLSession intentionally allow a cached session to be resumed at most once? Or can the same Session ID be resumed multiple times until it expires / is evicted from the cache? Without changing the overall LAN dashcam product model, how should the server be configured—e.g. moving to TLS 1.3 and/or HTTP/2—so that iOS clients can resume via Session Ticket and/or Session ID multiple times? What we have already ruled out / observed The client already uses a shared long-lived URLSession / Alamofire Session (we do not create a new session per request) The server often returns Connection: close, so each request uses a new TCP connection; we are discussing TLS session resumption across connections, not HTTP keep-alive We occasionally see TLS time of only ~10–20 ms, which suggests at least one successful session resumption has occurred

userlog.txt We've run into some HTTP request errors, details as follows: We're currently at a loss because restarting the app doesn't help, only rebooting the phone restores things to normal. Based on tracking data, the occurrence rate for users is about 0.033%, and it's only happening on iOS, Android is fine. iOS operating system versions: 14-27 are all affected. The same issue appears in Rust, Flutter, and C/C++. Rust： 2026-07-11-19:39:22.252+0800|F4E26069-2D7E-4D5F-8B53-664E012B2CA7|UPLogDefaultLogger|DEBUG|测试模式|1023629905|[userdomain_rust/rust_userdomain/src/operator/device_ops/refresh_device_list_op.rs:61]query_device_list error: HttpRequstFaild(Reqwest(reqwest::Error { kind: Request, url: "https://zj.haier.net/api-gw/wisdomdevice/device/v11/family/devices?familyId=ALL&filterFlag=false", source: hyper_util::client::legacy::Error(Connect, ConnectError("tcp connect error", 36.156.179.34:443, Os { code: 49, kind: AddrNotAvailable, message: "Can't assign requested address" })) })) Flutter： 2026-07-11-15:29:02.718371+0800|b2257ae8-f7d8-41d0-8811-2ff1824f95d9|UpPlugins|ERROR|正常模式|1023629905|level:error tag:smart_home msg:getWholeHousePreferenceSetting err: DioException [unknown]: null Error: SocketException: Connection failed (OS Error: Can't assign requested address, errno = 49), address = zj.haier.net, port = 443 C/C++： 2026-07-11-19:39:15.247588+0800|a991af96-bf02-4b94-a437-d4f7efc249ff|uSDK|ERROR|正常模式|1023629905|[CAE][[cae_sock_no_ssl_last_err:869][connect fd 122 ret -1 err 49: Can't assign requested address] ] Native iOS HTTP interface requests work fine, for example when using AFNetworking. Looking for your help~

We have an application which is written in Swift, which activates Transparent Proxy network extension. Our Transparent Proxy module is a system extension, which is exposing an app proxy provider interface (We are using NETransparentProxyProvider class and in extension’s Info.plist we use com.apple.networkextension.app-proxy key.) Sometimes we have observed that on starting the transparent proxy extension, the startProxy overridden delegate method(override func startProxy(options: [String : Any]?, completionHandler: @escaping (Error?) -> Void) {) in our AppProxyProvider class which is derived from NETransparentProxyProvider being called more than once for the same extension(pid). This leads to Over-resume of an object crash as we invoke setTunnelNetworkSettings inside the startProxy delegate. As this is controlled by the system, we are not sure why this delegate being called more than once sometimes even if we call the start TransparentProxy only once. Note that, this issue is seen only in Mac OS Tahoe. Apple Feedback ticket: FB21464147 (startProxy delegate for NETransparentProxyProvider class is being called twice for the same pid extension sometimes)

I've a iOT companion app, in which I'll connect to iOT's Wi-Fi and then communicate the device with APIs, for the above functionality we needed local network permission So we enabled neccessary keys in info.plist and at the time of App Launch we trigger local network permission using the following code info.plist <string>This app needs local network access permission to connect with your iOT device and customize its settings</string> <key>NSBonjourServices</key> <array> <string>_network-perm._tcp</string> <string>_network-perm._udp</string> </array> Network Permission Trigger Methods import Foundation import MultipeerConnectivity class NetworkPermissionManager: NSObject { static let shared = NetworkPermissionManager() private var session: MCSession? private var advertiser: MCNearbyServiceAdvertiser? private var browser: MCNearbyServiceBrowser? private var permissionCallback: ((String) -> Void)? func requestPermission(callback: @escaping (String) -> Void) { self.permissionCallback = callback do { let peerId = MCPeerID(displayName: UUID().uuidString) session = MCSession(peer: peerId, securityIdentity: nil, encryptionPreference: .required) session?.delegate = self advertiser = MCNearbyServiceAdvertiser( peer: peerId, discoveryInfo: nil, serviceType: "network-perm" ) advertiser?.delegate = self browser = MCNearbyServiceBrowser( peer: peerId, serviceType: "network-perm" ) browser?.delegate = self advertiser?.startAdvertisingPeer() browser?.startBrowsingForPeers() // Stop after delay DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) { [weak self] in self?.stopAll() // If no error occurred until now, consider permission triggered self?.permissionCallback?("granted") self?.permissionCallback = nil } } catch { permissionCallback?("error: \(error.localizedDescription)") permissionCallback = nil } } func stopAll() { advertiser?.stopAdvertisingPeer() browser?.stopBrowsingForPeers() session?.disconnect() } } extension NetworkPermissionManager: MCSessionDelegate { func session(_: MCSession, peer _: MCPeerID, didChange _: MCSessionState) {} func session(_: MCSession, didReceive _: Data, fromPeer _: MCPeerID) {} func session(_: MCSession, didReceive _: InputStream, withName _: String, fromPeer _: MCPeerID) {} func session(_: MCSession, didStartReceivingResourceWithName _: String, fromPeer _: MCPeerID, with _: Progress) {} func session(_: MCSession, didFinishReceivingResourceWithName _: String, fromPeer _: MCPeerID, at _: URL?, withError _: Error?) {} } extension NetworkPermissionManager: MCNearbyServiceAdvertiserDelegate { func advertiser(_: MCNearbyServiceAdvertiser, didReceiveInvitationFromPeer _: MCPeerID, withContext _: Data?, invitationHandler: @escaping (Bool, MCSession?) -> Void) { invitationHandler(false, nil) } func advertiser(_: MCNearbyServiceAdvertiser, didNotStartAdvertisingPeer error: Error) { print("❌ Advertising failed: \(error)") if let nsError = error as NSError?, nsError.domain == NetService.errorDomain, nsError.code == -72008 { permissionCallback?("denied") } else { permissionCallback?("error: \(error.localizedDescription)") } permissionCallback = nil stopAll() } } extension NetworkPermissionManager: MCNearbyServiceBrowserDelegate { func browser(_: MCNearbyServiceBrowser, foundPeer _: MCPeerID, withDiscoveryInfo _: [String: String]?) {} func browser(_: MCNearbyServiceBrowser, lostPeer _: MCPeerID) {} func browser(_: MCNearbyServiceBrowser, didNotStartBrowsingForPeers error: Error) { print("❌ Browsing failed: \(error)") if let nsError = error as NSError?, nsError.domain == NetService.errorDomain, nsError.code == -72008 { permissionCallback?("denied") } else { permissionCallback?("error: \(error.localizedDescription)") } permissionCallback = nil stopAll() } }``` I want to satisfy this following cases but it's not working as expected # Case1 Working App launches --> trigger permission using above code --> user granted permission --> connect to iOT's Wi-Fi using app --> Communicate via Local API ---> should return success response # Case2 Not working App launches --> trigger permission using above code --> user denied permission --> connect to iOT's Wi-Fi using app --> Communicate via Local API ---> should throw an error I double checked the permission status in the app settings there also showing disabled state In my case case 2 is also return success, even though user denied the permission I got success response. I wonder why this happens the same above 2 cases working as expected in iOS 17.x versions

Hi, I’m using Network Framework to implement a UDP client via NWConnection, and I’m looking for clarification about the correct and fully safe shutdown procedure, especially regarding resource release. I have initiated some pending receive calls on the NWConnection (using receive). After calling connection.cancel(), do we need to wait for the cancellation of these pending receives? As mentioned in this thread, NWConnection retains references to the receive closures and releases them once they are called. If a receive closure holds a reference to the NWConnection itself, do we need to wait for these closures to be called to avoid memory leaks? Or, if there are no such retained references, we don't need to wait for the cancellation of the pending I/O and cancelled state for NWConnection?

I am planning an iOS security and content-blocking app for unmanaged consumer iPhones. The app would not provide a traditional VPN service. It would not offer: Remote VPN servers Geographic location switching Access to a private corporate network IP-address masking as a service Anonymous browsing Instead, the app would allow the user to: View destination domains contacted by the device Classify destinations such as trackers, advertising, analytics, or potentially malicious domains Manually block selected domains Keep connection history and filtering decisions on the device I understand that NEFilterDataProvider and NEFilterControlProvider are the APIs intended for network content filtering. However, according to TN3134, these providers are not generally deployable for an unmanaged adult consumer iPhone. I also understand that TN3120 says NEPacketTunnelProvider should not be used as a general-purpose local content filter. This appears to leave a gap for an unmanaged consumer security app whose core feature is user-controlled, system-wide domain blocking. I am considering whether NETunnelProviderManager with an NEPacketTunnelProvider could support the feature, but I do not want to use the packet-tunnel API outside its supported purpose. My questions are: Is there currently a supported Network Extension architecture for system-wide, user-controlled domain blocking on an unmanaged adult consumer iPhone? Can an app with this purpose use NEPacketTunnelProvider, or would that necessarily be considered the unsupported general-purpose filtering use described in TN3120? If such an architecture is supported, could an app with this purpose be treated as an approved security or content-blocking provider under Guideline 5.4 rather than as an app offering a traditional VPN service? App Review Guideline 5.4 states that apps offering VPN services must be submitted by developers enrolled as organizations. It also states that parental-control, content-blocking, and security apps from approved providers may use NEVPNManager. For an app that does not provide a remote VPN service but uses Apple’s VPN configuration infrastructure only for local security and user-controlled blocking, must the developer still enroll as an organization, or may an individual Apple Developer Program member submit it?

Hello Apple Developer Technical Support / Engineering Team, We are currently developing an iOS application that utilizes Wi-Fi Aware (NAN) for peer-to-peer data transfer between iOS devices. We are in the process of optimizing our data transmission performance and are evaluating the different data path configurations available. Specifically, we would like to understand the performance characteristics and throughput differences between the Real-Time mode and the Bulk mode in the iOS Wi-Fi Aware implementation. Could you please provide clarification on the following points? Maximum Throughput: Between Real-Time mode and Bulk mode, which one is designed to provide a higher maximum throughput for continuous data transfer?

Dear Apple: 1、We want to create a socket application using the C language interface on the WiFi Aware channel, utilizing native socket APIs such as socket, connect, bind, etc., to transmit data through the established WiFi Aware channel. However, we wrote a demo and tested it. On the iOS side, when initiating a socket connect, we received error code 65. We also used the IPv6 protocol. We would like to ask for help: Is it impossible to use native socket APIs for programming on the WiFi Aware channel? 2、If native sockets are not available, which interfaces are recommended for WiFi Aware communication on iOS? Thanks.

Hi Team, I'm trying to understand the behavior of the following API: HTTPCookieStorage.shared.setCookies(_:for:mainDocumentURL:) Specifically, does this API persist cookies synchronously, or does it perform the storage asynchronously in the background? Our use case is storing FCAP (frequency capping) cookies so they persist across app sessions. We call setCookies(_:for:mainDocumentURL:) and want to know whether the cookies are guaranteed to be written before the method returns, or if the actual persistence happens asynchronously. I couldn't find documentation describing the persistence semantics of this API, so I'd appreciate any clarification or guidance from Apple or anyone familiar with its implementation. Thanks

Filed as FB23904785 with pcaps, a mid-episode sysdiagnose, & a userspace test harness. Posting here because the behavior localizes to the receive-window computation in xnu & I'd value a sanity check from anyone who knows what changed in this area for 27. On 26A5378n (MacBook Air M2, RTL8156B 2.5GbE via the in-kernel AppleUSBNCM driver), TCP downloads on the wired interface intermittently drop to 6-10 Mbps for stretches of minutes to 40 minutes, then recover on their own. Wi-Fi on the same machine pulls 50-70 Mbps from the same servers in the same seconds. Packet captures show why: during these stretches the kernel advertises a 5,440-byte receive window from the first post-handshake ACK & doubles it on 1.000 s ± 0.01 s wall-clock boundaries, seven doublings in a row, in two separate connections started 6.5 minutes apart, while bytes-per-interval varied 16x. Byte-count triggers can't produce byte-rate-invariant timing; that's a clock. What I ruled out inside a live occurrence: SO_RCVBUF of 4 MB (getsockopt-verified; identical staircase, so it isn't autotuning), ECN on/off (three toggles, no change), both link_heuristics sysctls, the WAN (during one occurrence ICMP loss was WORSE on Wi-Fi, 20% vs 10%, yet Wi-Fi ran 5x faster), & the wire itself (0.1% retransmissions, ACK timestamp-echo p50 43 ms, zero zero-window advertisements). TCP_CONNECTION_INFO confirms the on-wire numbers: tcpi_rcv_wnd 10,880 at t=2 s against a 4 MB buffer that stays 97% empty, tcpi_srtt 41 ms. The throttled flow itself hit 32.7 Mbps at t=7 s once the staircase reached 347 KB, so path capacity was there the whole time. The signature resembles a receiver-side LEDBAT governor (RFC 9840 describes exposing a reduced window through the receive window; tcp_rledbat.c in published xnu clamps recwin for sockets flagged receive-background). Two things don't add up though. First, I ported the published tcp_rledbat.c to userspace & drove it with the exact packet timeline from my capture: no parameterization reproduces constant 2x steps on one-second boundaries, because every growth law in that file counts bytes or RTTs, not seconds. Second, kern.ipc.throttle_best_effort reads 1 on a clean boot of this beta with no sysctl.conf, no profiles, & no third-party launch items, while published xnu initializes it to 0. That switch arms the demotion of best-effort sockets to receive-background on interfaces that recently carried realtime-marked traffic. Questions: did the receive-window governor change in 27, & did the throttle_best_effort default flip intentionally? And is there a supported way to see which sockets carry SOF1_TRAFFIC_MGT_TCP_RECVBG at runtime, to pin down what's marking these flows? Happy to attach anything from the evidence set to the FB or run diagnostics on request; the fault reproduces several times a day here.

Hello! Users of my app observed behaviour that some apps stopped working after update to 15.7.8 via Beta channel with transparent proxy network extension on. The app receives Protocol not available error, and I see setsockopt SO_FLOW_DIVERT_TOKEN failed [42: Protocol not available] error in Console. To reproduce, create two rules in basic NETransparentProxyProvider: [[NENetworkRule alloc] initWithDestinationNetwork:nil prefix:0 protocol:NENetworkRuleProtocolTCP], [[NENetworkRule alloc] initWithDestinationNetwork:nil prefix:0 protocol:NENetworkRuleProtocolUDP], You may even return NO in handleNewFlow, it does not matter. After that, Safari won't open some sites, and Weather app will work unreliably. Do anyone knows any workaround for this problem? I've also create a relevant FB23788740.

Version: MacOS 12.1 When I was using NETransparentProxyProvider, I overrive handleNewFlow, handleNewUDPFlow , and return true for some process, and then call - (void)openWithLocalEndpoint:(NWHostEndpoint *)localEndpoint completionHandler:(void (^)(NSError *error))completionHandler; at the beginning, work fine, buy sometime, when I visited qiye.163.com website, I often got an error when I do code below: - (void)writeData:(NSData *)data withCompletionHandler:(void (^)(NSError *error))completionHandler; Error Domain=NEAppProxyFlowErrorDomain Code=1 "The operation could not be completed because the flow is not connected" UserInfo={NSLocalizedDescription=The operation could not be completed because the flow is not connected , and the whole computer could not access the Internet , handleNewFlow and handleNewUDPFlow both are no longer called, unless I turn off the VPN. Turn off VPN and then Internet can be access