General: DevForums tag: Network Extension Network Extension framework documentation Network Extension and VPN Glossary DevForums post Debugging a Network Extension Provider DevForums post Exporting a Developer ID Network Extension DevForums post Network Extension vs ad hoc techniques on macOS DevForums post Extra-ordinary Networking DevForums post Wi-Fi management: Wi-Fi Fundamentals DevForums post TN3111 iOS Wi-Fi API overview technote How to modernize your captive network developer news post iOS Network Signal Strength DevForums post See also Networking Resources. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com"

Can an Persional developer account develop, debug, and publish Network Extension apps?

Hi, i'm working on an endpoint security extension loader and implement several callbacks from delegate object OSSystemExtensionRequestDelegate the callback i'm interested in is : public func request(_ request: OSSystemExtensionRequest, didFinishWithResult result: OSSystemExtensionRequest.Result); public func requestNeedsUserApproval(_ request: OSSystemExtensionRequest); I've noticed that if I manually approve the extension long time after it was activated, the extension process goes up, but the callback isn't being called. The requestNeedUserApproval callback always gets called. I see in the unified logs that when the extension goes from activated_waiting_for_user -> activated_enabling -> activated_enabled Than the request callback doesn't get called. But whenever the extension goes activated_waiting_for_user -> activated_disabled The request callback gets called. (this is counter intuitive since we expected the state activated_disabled may hint that the extension failed to be activated somehow) Any Idea why my callback doesn't gets called if the extension gets approved long after it was activated ?

We are checking for cellular mode using the code below. When the code below is executed, is it correct to convey the status value of the actually connected cellular environment? Sometimes HSDPA or WCDMA is output. I would like to inquire under what conditions the value is output. [Code] func getCellularConnectionType() -> String { if #available(iOS 14.1, *) { if let radioAccessTechnology = networkInfo.serviceCurrentRadioAccessTechnology?.values.first { Debug.log("Radio Access Technology: (radioAccessTechnology)") switch radioAccessTechnology { case CTRadioAccessTechnologyLTE: return "LTE" case CTRadioAccessTechnologyNRNSA: return "5G-NSA" case CTRadioAccessTechnologyNR: return "5G-SA" default: return "ETC" } } } return "Cellular" }

I have tests where I connect to NEPacketTunnelProvider. I run tests with circleci and fastlane, on self hosted intel and arm macs. I updated macs from macOS 13 to macOS 14 and the tests on arm stopped connecting, while the same tests on intel kept working as usual. Moreover, I noticed the tests don't work when run from circleci and fastlane. If I cancel the job and click "connect" myself on the app that stayed hanging from the cancelled tests, the connection will succeed. But if the tests are running, the connection will fails. Running the tests from xcode succeeds too. These are the logs from the tunnel. Could you suggest me where to dig? Or maybe you can see the issue from the logs? Tunnel logs when they fail

I've been trying very unsuccessfully to get the Filtering Network Traffic example code to work. I've read many forum posts but I still wasn't able to figure it out. I download the example project and set my development team for both targets. From then on the project is configured to create unique bundle identifiers and app group. Signing and provisioning profile is created and managed by Xcode with all the necessary entitlements. I am able to build the app (debug with provisioning profile) and then copy it to /Applications. I open the app, click start, enable and allow the network extension. Activity Monitor shows that the extension is running. But when I test local connections to port 8888 nothing happens in the app, the connection are just allowed. I tested with the following setup: create a local webserver with python3 -m http.server 8888 and make a request via curl and the webbrowser normal tcp connection with nc (nc -l 8888 and nc localhost 8888) I added lots of logging and I can see that the startFilter method is called, but never the handleNewFlow method. The only error I see in Console is networkd_settings_read_from_file Sandbox is preventing this process from reading networkd settings file at "/Library/Preferences/com.apple.networkd.plist", please add an exception. but don't know what to do about that. I also read the debugging guide (very helpful). I'm used to jump through a lot of hoops with this stuff, but I can't figure out what the problem is.

hello, we're currently working on a way to adapt the behavior of our app when the device is running with a low free memory remaining, or a bad network. For the network, we though about implementing a speedtest, but the issue with this solution is that we want to test regularly the quality of the network, so if the device is running with a poor/bad network, the speedtest with stuck the app. I was looking for other way to check the displayed informations in the status bar: private func getWiFiRSSI() -> Int? { let app = UIApplication.shared var rssi: Int? let exception = tryBlock { guard let statusBar = app.value(forKey: "statusBar") as? UIView else { return } if let statusBarMorden = NSClassFromString("UIStatusBar_Modern"), statusBar .isKind(of: statusBarMorden) { return } guard let foregroundView = statusBar.value(forKey: "foregroundView") as? UIView else { return } for view in foregroundView.subviews { if let statusBarDataNetworkItemView = NSClassFromString("UIStatusBarDataNetworkItemView"), view .isKind(of: statusBarDataNetworkItemView) { if let val = view.value(forKey: "wifiStrengthRaw") as? Int { rssi = val break } } } } if let exception = exception { print("getWiFiRSSI exception: \(exception)") } return rssi } I've checked the AppStore Guidelines but I'm not sure that this kind of code will not be subject to rejection by the Review team. Anyone having trying to submit with a similar approach? Did you already managed to monitor network regularly, without using a speedtest? Thanks for the help!

Hi, all. We have a camera with only one WiFi module. It supports AP and STA modes coexisting, but the WiFi of AP and STA can only be in the same channel at the same time, that is, 2.4G or 5G. In the initial state, the App is connected to the camera through 5G WiFi, and the camera is in AP mode. When entering the network configuration mode, the camera will start the STA mode, and the AP and STA modes coexist. When the user selects 2.4G WiFi, the AP mode will switch from 5G to 2.4G. Android's WiFi and socket are not disconnected, iOS's socket will be disconnected 100%, and WiFi may be disconnected. What is the reason for this? Is there any way to solve it?

We have Mac OS VM which has two network interfaces and both are active. In our application we need “State:/Network/Global/IPv6” to do some task but on this machine it seems to be missing, however if we disable one of the interface then the same setting seems to be available and our code works fine. Please find the attached screenshots of working & non-working details:

Hi, I'm adding a Content Filtering (FilterDataProvider) on macOS to an existing app and using MDM to avoid user interaction. I start by pushing the following payloads to my machine: com.apple.system-extension-policy com.apple.webcontent-filter And then installing notarized pkg containing my app and the NE. Inspecting the system logs shows the following error: neagent Failed to find a com.apple.networkextension.filter-data extension inside of app com.company_name.app_name.daemon And calling submit(request: .activationRequest(forExtensionWithIdentifier: bundleId, queue: queue)) results in: Missing entitlement com.apple.developer.system-extension.install Installing from Xcode on a SIP disabled machine works fine and both NE and CF are working as expected. I followed the steps mentioned here https://developer.apple.com/forums/thread/737894 however the embedded entitlements already contained -systemextension suffix so I'm not sure if re signing and the subsequent steps are needed. I also double checked that com.apple.developer.system-extension.install is present, certificates are not expired and that get-task-allow is not present in the embedded profile. Here is what my release entitlement file looks like: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>com.apple.developer.networking.networkextension</key> <array> <string>content-filter-provider-systemextension</string> </array> <key>com.apple.security.application-groups</key> <array> <string>com.company_name.app_name.network-extension.content-filter</string> </array> </dict> and my release app entitlement: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>com.apple.developer.endpoint-security.client</key> <true/> <key>com.apple.developer.networking.networkextension</key> <array> <string>content-filter-provider-systemextension</string> </array> <key>com.apple.developer.system-extension.install</key> <true/> </dict> </plist> redacted logs @eskimo may I ask for your help here!

Hi everyone, Our app helps users block adult websites to promote focus and digital wellness. During the App Store review, it was flagged under Guideline 2.5.1 for using a VPN profile to block content, with Apple advising us to remove this feature. Since blocking adult content is core to our app, we’re looking for compliant alternatives: Can Network Extensions Framework (e.g., NEDNSProxyProvider) be used for on-device filtering? Would pre-configured safe DNS (e.g., CleanBrowsing) be acceptable? Are there compliant examples of similar apps? Any advice on achieving this functionality within Apple’s guidelines would be greatly appreciated. Thanks!

We want to ressolve dns for predefined sets of private app domains. We've added this rule: NENetworkRule(destinationHost: NWHostEndpoint(hostname: Private Domain1(example.com), port: 53), protocol: .UDP) As per apple documentation: A rule that matches all DNS queries/responses for hosts in the example.com domain. do you think it will work i.e it will forward DNS requests UDP flow to transparent provider in all the cases? or do you think the text is a bit misleading. it should instead say: "A rule that matches all DNS queries/responses for nameservers in the example.com domain"? This rule that look for port 53 of that domain only works if the system really asks a nameserver of that specific domain, right? So, what if a local DNS server or a different nameserver are taking care of the resolution?

I need to check how long we can run an app in background which act as a consumer of data / control filter. What is the max time we get to run our app in background without any of these app strategies? https://developer.apple.com/documentation/backgroundtasks/choosing-background-strategies-for-your-app

On iOS beta, monitoring network usage using the getifaddrs API sporadically causes system volume spikes. This happens even though the application does not interact with any audio-related code. The issue persists across different polling intervals (e.g., 0.05s to 1s) and only occurs when invoking getifaddrs. Replacing the API calls with mock data eliminates the problem, suggesting a potential issue with getifaddrs in the beta environment. The application updates UI elements based on network activity, but the volume spikes occur independently of UI or other observable app behavior. Steps to Reproduce: Create an app that monitors network usage using the getifaddrs API. Fetch network statistics on a timer (e.g., every 0.05 seconds). Observe system behavior while running the app on iOS beta. Note sporadic volume spikes during app runtime. Expected Result: Polling network usage with getifaddrs should not affect system volume or other unrelated resources. Actual Result: System volume spikes occasionally when network statistics are retrieved using getifaddrs. iOS 18.2 Beta, Tested on physical device ( iPhone 15 Pro )

Hi, TLDR: On iOS, when my PacketTunnel is running, can I exclude DNS requests from going into the tunnel? I have a test app, using Apple's AsyncDNSResolver, that makes a DNS call and it works when the tunnel is not running. If the tunnel is running it times out after 30 seconds and I get the error -65568. Here's how I'm setting up the tunnel func setup(tunnelRemoteAddress: String) { let settings = NEPacketTunnelNetworkSettings(tunnelRemoteAddress: tunnelRemoteAddress) settings.ipv4Settings = NEIPv4Settings(addresses: [tunnelRemoteAddress], subnetMasks: ["255.255.255.255"]) settings.ipv4Settings?.includedRoutes = [NEIPv4Route.default()] let proxySettings = NEProxySettings() proxySettings.httpEnabled = true proxySettings.httpServer = NEProxyServer(address: ProxyServerConfiguration.host, port: ProxyServerConfiguration.port) proxySettings.httpsEnabled = true proxySettings.httpsServer = NEProxyServer(address: LocalProxyServerConfiguration.host, port: LocalProxyServerConfiguration.port) proxySettings.excludeSimpleHostnames = true proxySettings.exceptionList = nil let dnsSettings = NEDNSSettings(servers: ["8.8.8.8"]) settings.dnsSettings = dnsSettings settings.proxySettings = proxySettings setTunnelNetworkSettings(settings) { error in // ... } } I've tried all combinations of setting/excluding the NEDNSSettings but the DNS call always fails when the tunnel is running. Thanks for any help.

Whenever I'm working on my content filter for macOS, I usually keep SIP disabled and with developer mode on (systemextensionsctl) as a convenience. The issue: content filter stopped receiving any kind of traffic when SIP is disabled. I don't see any log lines in Console for new flows, and the filter can't block anything, since it doesn't get any flows. Issue started yesterday. I tried several things and did some investigation, here are some findings: Reboot: rebooting did not fix the issue (while keeping SIP disabled). Reenabling SIP fixes the issue for both App Store and Xcode builds. Code: latest published version also stopped working with SIP disabled. This version is stable and confirmed to work as reported by users. Clean Xcode + rebuild did not fix the issue. Lastly, I inspected the logs and did not see any errors standing out. I noticed the filter does get started (startFilter is called) and registered, but after that there are no errors/new flows or anything, just silence (logs below). com.apple.networkextension default 15:22:22.270746-0300 : Calling startFilterWithCompletionHandler com.extension.MyExtension info 15:22:22.270998-0300 Success applying filter settings com.apple.networkextension debug 15:22:22.272705-0300 NESMFilterSession[My Extension:B9F3F30E-E0E0-4E53-8B32-EFC285E3CF6A]: Checking providerBundleIdentifier com.extension.MyExtension for pluginClass 4 com.apple.networkextension debug 15:22:22.272717-0300 Checking for com.extension.MyExtension - com.apple.networkextension.filter-data com.apple.networkextension default 15:22:22.272728-0300 Found 1 registrations for com.extension.MyExtension (com.apple.networkextension.filter-data) com.apple.networkextension debug 15:22:22.272778-0300 NESMFilterSession[My Extension:B9F3F30E-E0E0-4E53-8B32-EFC285E3CF6A]: com.extension.MyExtension is registered for pluginClass 4 Here are some additional info about my system: macOS 15.1 Between yesterday and today, the only new Installation is XProtectPlistConfigData at 12:10AM Thanks!

We use as content filter in our app to monitor flows, we gather data about the flow and block flows deemed suspicious. Our content filter is activated/deactivated by a UI app but the flows are reported via XPC to a separate daemon process for analysis. As of macOS 15, we are seeing cases where flows are missing or flows are not received at all by the content filter. The behaviour is not consistent, some devices seem to receive flows normally but others don't. It appears Intel devices are much less prone to showing the problem, whereas Arm devices routinely exhibit missing flows. On macOS 14 or earlier, there is no sign of missing flows. Testing on earlier beta versions of macOS 15 did not appear to show the problem, however I can't rule out if issue was present but it wasn't spotted. Experimenting with simple examples of using a content filter (e.g. QNE2FilterMac) does not appear to reproduce the issue. Questions, What has changed between macOS 14 and 15 that could be the cause of the lack of flows? Is our approach to using an app activated content filter reporting to a daemon connected via XPC unsupported?

Hello all, I have a question, I am developing an application that uses the apply() function of the NEHotspotConfigurationManager class to switch the Wifi of the device. In the completionHandler of the apply() function, the error argument contains “Internal Error(8)” and the wifi switching may fail. We have never seen this problem during development, and since it occurs only in the market, we are at a loss as to the cause and countermeasure. Do you know the cause of the “Internal Error(8)” and how to fix it? A similar phenomenon has already been discussed in the following thread, but after countermeasures were taken in iOS12, it also occurs in iOS13 and later and no progress has been made since then. https://developer.apple.com/forums/thread/107851 I would appreciate it if someone could clarify what is happening with this error, as there is not much information on the web regarding this error. Thank you in advance.

Hello, I have a company laptop thats connected to the internet without a VPN. I need to be able to resolve my company's sub domains using a specific dns server, and have all other domains resolved by the system wide name server. In windows, this is trivial to do. In an admin powershell I run "Add-DnsClientNrptRule -Namespace ".foo.mycompany.com" -Nameserver "127.0.0.1" and resolution requests for *.foo.mycompany.com is sent to a name server running on the localhost. All other dns resolution requests are handled by the system configured resolver. MacOS does have the /etc/resolver/ solution for this, but my understanding from these forums is that this is not the recommended approach. Note - I have tried it and it works. AFAIU, the recommended approach is to create a system Network extension using NEDNSProxyProvider, override handleNewFlow() and do what's necessary. The issue with this solution is that it requires handling all the dns flow parsing of DNS datagrams to extract the host forwarding the datagrams to the appropriate dns server Handle responses. Deal with flow control Handle edge cases. I was hoping for something much simpler than us needing to implement datagram parsing. Could you please shed light on our options and how we could proceed ?

I'm use iPad OS 17.5.1, when I try to use socket to connect to an ipv6 address created by PacketTunnelProvider in my iOS device, an error occurs. Here is the code to create socket server and client: #include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;sys/socket.h&gt; #include &lt;netinet/in.h&gt; #include &lt;arpa/inet.h&gt; #include &lt;unistd.h&gt; int dx_create_ipv6_server(const char *ipv6_address, int port) { int server_fd; struct sockaddr_in6 server_addr; server_fd = socket(AF_INET6, SOCK_STREAM, 0); if (server_fd == -1) { perror("socket() failed"); return -1; } memset(&amp;server_addr, 0, sizeof(server_addr)); server_addr.sin6_family = AF_INET6; server_addr.sin6_port = htons(port); if (inet_pton(AF_INET6, ipv6_address, &amp;server_addr.sin6_addr) &lt;= 0) { perror("inet_pton() failed"); close(server_fd); return -1; } if (bind(server_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) == -1) { perror("bind() failed"); close(server_fd); return -1; } if (listen(server_fd, 5) == -1) { perror("listen() failed"); close(server_fd); return -1; } printf("Server is listening on [%s]:%d\n", ipv6_address, port); return server_fd; } int dx_accept_client_connection(int server_fd) { int client_fd; struct sockaddr_in6 client_addr; socklen_t client_addr_len = sizeof(client_addr); client_fd = accept(server_fd, (struct sockaddr *)&amp;client_addr, &amp;client_addr_len); if (client_fd == -1) { perror("accept() failed"); return -1; } char client_ip[INET6_ADDRSTRLEN]; inet_ntop(AF_INET6, &amp;client_addr.sin6_addr, client_ip, sizeof(client_ip)); printf("Client connected: [%s]\n", client_ip); return client_fd; } int dx_connect_to_ipv6_server(const char *ipv6_address, int port) { int client_fd; struct sockaddr_in6 server_addr; client_fd = socket(AF_INET6, SOCK_STREAM, 0); if (client_fd == -1) { perror("socket() failed"); return -1; } memset(&amp;server_addr, 0, sizeof(server_addr)); server_addr.sin6_family = AF_INET6; server_addr.sin6_port = htons(port); if (inet_pton(AF_INET6, ipv6_address, &amp;server_addr.sin6_addr) &lt;= 0) { perror("inet_pton() failed"); close(client_fd); return -1; } if (connect(client_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) == -1) { perror("connect() failed"); close(client_fd); return -1; } printf("Connected to server [%s]:%d\n", ipv6_address, port); close(client_fd); return 0; } @implementation SocketTest + (void)startSever:(NSString *)addr port:(int)port { [[NSOperationQueue new] addOperationWithBlock:^{ int server_fd = dx_create_ipv6_server(addr.UTF8String, port); if (server_fd == -1) { return; } int client_fd = dx_accept_client_connection(server_fd); if (client_fd == -1) { close(server_fd); return; } close(client_fd); close(server_fd); }]; } + (void)clientConnect:(NSString *)addr port:(int)port{ [[NSOperationQueue new] addOperationWithBlock:^{ dx_connect_to_ipv6_server(addr.UTF8String, port); }]; } @end PacketTunnelProvider code: override func startTunnel(options: [String : NSObject]?, completionHandler: @escaping (Error?) -&gt; Void) { let settings = NEPacketTunnelNetworkSettings(tunnelRemoteAddress: "fd84:306d:fc4e::1") let ipv6 = NEIPv6Settings(addresses: ["fd84:306d:fc4e::1"], networkPrefixLengths: 64) settings.ipv6Settings = ipv6 setTunnelNetworkSettings(settings) { error in if error == nil { self.readPackets() } completionHandler(error) } } private func readPackets() { // do nothing packetFlow.readPackets { [self] packets, protocols in self.packetFlow.writePackets(packets, withProtocols: protocols) self.readPackets() } } At main target, in viewcontroller's viewDidAppear, after starting the VPN, executed following code: [SocketTest startSever:@"fd84:306d:fc4e::1" port:12345]; sleep(3); [SocketTest clientConnect:@"fd84:306d:fc4e::1" port:12345]; The startSever is executed correctly, but when executing： connect(client_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) in clientConnect, the code is blocked until it times out and returns -1. **Even if I use GCDAsyncSocket or BlueSocket, I get the same error. The strange thing is that if I use the ipv4 address in PacketTunnelProvider, and change the above code to the ipv4 version and connect to ipv4 address, or use GCDAsyncSocket to perform the corresponding operation, it can be executed correctly. ** I tried to search Google for problems with ios-related ipv6 addresses, but I still couldn't find a solution. Is this a bug in the ios system or is there something wrong with my code? I hope to get your help! Stackoverflow url: iOS Socket cannot connect ipv6 address when use PacketTunnelProvider

When I try to use socket to connect to an ipv6 address created by PacketTunnelProvider in my iOS device, an error occurs. Here is the code to create socket server and client: #include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;sys/socket.h&gt; #include &lt;netinet/in.h&gt; #include &lt;arpa/inet.h&gt; #include &lt;unistd.h&gt; int dx_create_ipv6_server(const char *ipv6_address, int port) { int server_fd; struct sockaddr_in6 server_addr; server_fd = socket(AF_INET6, SOCK_STREAM, 0); if (server_fd == -1) { perror("socket() failed"); return -1; } memset(&amp;server_addr, 0, sizeof(server_addr)); server_addr.sin6_family = AF_INET6; server_addr.sin6_port = htons(port); if (inet_pton(AF_INET6, ipv6_address, &amp;server_addr.sin6_addr) &lt;= 0) { perror("inet_pton() failed"); close(server_fd); return -1; } if (bind(server_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) == -1) { perror("bind() failed"); close(server_fd); return -1; } if (listen(server_fd, 5) == -1) { perror("listen() failed"); close(server_fd); return -1; } printf("Server is listening on [%s]:%d\n", ipv6_address, port); return server_fd; } int dx_accept_client_connection(int server_fd) { int client_fd; struct sockaddr_in6 client_addr; socklen_t client_addr_len = sizeof(client_addr); client_fd = accept(server_fd, (struct sockaddr *)&amp;client_addr, &amp;client_addr_len); if (client_fd == -1) { perror("accept() failed"); return -1; } char client_ip[INET6_ADDRSTRLEN]; inet_ntop(AF_INET6, &amp;client_addr.sin6_addr, client_ip, sizeof(client_ip)); printf("Client connected: [%s]\n", client_ip); return client_fd; } int dx_connect_to_ipv6_server(const char *ipv6_address, int port) { int client_fd; struct sockaddr_in6 server_addr; client_fd = socket(AF_INET6, SOCK_STREAM, 0); if (client_fd == -1) { perror("socket() failed"); return -1; } memset(&amp;server_addr, 0, sizeof(server_addr)); server_addr.sin6_family = AF_INET6; server_addr.sin6_port = htons(port); if (inet_pton(AF_INET6, ipv6_address, &amp;server_addr.sin6_addr) &lt;= 0) { perror("inet_pton() failed"); close(client_fd); return -1; } if (connect(client_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) == -1) { perror("connect() failed"); close(client_fd); return -1; } printf("Connected to server [%s]:%d\n", ipv6_address, port); close(client_fd); return 0; } @implementation SocketTest + (void)startSever:(NSString *)addr port:(int)port { [[NSOperationQueue new] addOperationWithBlock:^{ int server_fd = dx_create_ipv6_server(addr.UTF8String, port); if (server_fd == -1) { return; } int client_fd = dx_accept_client_connection(server_fd); if (client_fd == -1) { close(server_fd); return; } close(client_fd); close(server_fd); }]; } + (void)clientConnect:(NSString *)addr port:(int)port{ [[NSOperationQueue new] addOperationWithBlock:^{ dx_connect_to_ipv6_server(addr.UTF8String, port); }]; } @end PacketTunnelProvider code: override func startTunnel(options: [String : NSObject]?, completionHandler: @escaping (Error?) -&gt; Void) { let settings = NEPacketTunnelNetworkSettings(tunnelRemoteAddress: "fd84:306d:fc4e::1") let ipv6 = NEIPv6Settings(addresses: ["fd84:306d:fc4e::1"], networkPrefixLengths: 64) settings.ipv6Settings = ipv6 setTunnelNetworkSettings(settings) { error in if error == nil { self.readPackets() } completionHandler(error) } } private func readPackets() { // do nothing packetFlow.readPackets { [self] packets, protocols in self.packetFlow.writePackets(packets, withProtocols: protocols) self.readPackets() } } At main target, in viewcontroller's viewDidAppear, after starting the VPN, executed following code: [SocketTest startSever:@"fd84:306d:fc4e::1" port:12345]; sleep(3); [SocketTest clientConnect:@"fd84:306d:fc4e::1" port:12345]; The startSever is executed correctly, but when executing： connect(client_fd, (struct sockaddr *)&amp;server_addr, sizeof(server_addr)) in clientConnect, the code is blocked until it times out and returns -1. Even if I use GCDAsyncSocket or BlueSocket, I get the same error. The strange thing is that if I use the ipv4 address in PacketTunnelProvider, and change the above code to the ipv4 version and connect to ipv4 address, or use GCDAsyncSocket to perform the corresponding operation, it can be executed correctly. I tried to search Google for problems with ios-related ipv6 addresses, but I still couldn't find a solution. Is this a bug in the ios system or is there something wrong with my code? I hope to get your help!