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 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 Network Extension (including Wi-Fi on iOS): See Network Extension Resources Wi-Fi Fundamentals TN3111 iOS Wi-Fi API overview Wi-Fi Aware framework documentation Wi-Fi on macOS: Forums tag: Core WLAN Core WLAN framework documentation Wi-Fi Fundamentals 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. 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. 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 WirelessInsights framework documentation iOS Network Signal Strength 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 work on a smart product that, for setup, uses a captive portal to allow users to connect and configure the device. It emits a WiFi network and runs a captive portal - an HTTP server operates at 10.0.0.1, and a DNS server responds to all requests with 10.0.0.1 to direct "any and all" request to the server. When iOS devices connect, they send a request to captive.apple.com/hotspot-detect.html; if it returns success, that means they're on the internet; if not, the typical behavior in the past has been to assume you're connected to a captive portal and display what's being served. I serve any requests to /hotspot-detect.html with my captive portal page (index.html). This has worked reliably on iOS18 for a long time (user selects my products WiFi network, iOS detects portal and opens it). But almost everyone who's now trying with iOS26 is having the "automatic pop up" behavior fail - usually it says "Error opening page - Hotspot login cannot open the page because the network connection was lost." However, if opening safari and navigating to any URL (or 10.0.0.1) the portal loads - it's just the iOS auto-detect and open that's not working iOS18 always succeeds; iOS26 always fails. Anybody have any idea what changes may have been introduced in iOS26 on this front, or anything I can do to help prompt or coax iOS26 into loading the portal? It typically starts reading, but then stops mid-read.

For important background information, read Extra-ordinary Networking before reading this. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" On Host Names I commonly see questions like How do I get the device’s host name? This question doesn’t make sense without more context. Apple systems have a variety of things that you might consider to be the host name: The user-assigned device name — This is a user-visible value, for example, Guy Smiley. People set this in Settings > General > About > Name. The local host name — This is a DNS name used by Bonjour, for example, guy-smiley.local. By default this is algorithmically derived from the user-assigned device name. On macOS, people can override this in Settings > General > Sharing > Local hostname. The reverse DNS name associated with the various IP addresses assigned to the device’s various network interfaces That last one is pretty much useless. You can’t get a single host name because there isn’t a single IP address. For more on that, see Don’t Try to Get the Device’s IP Address. The other two have well-defined answers, although those answers vary by platform. I’ll talk more about that below. Before getting to that, however, let’s look at the big picture. Big Picture The use cases for the user-assigned device name are pretty clear. I rarely see folks confused about that. Another use case for this stuff is that you’ve started a server and you want to tell the user how to connect to it. I discuss this in detail in Showing Connection Information in an iOS Server. However, most folks who run into problems like this do so because they’re suffering from one of the following misconceptions: The device has a DNS name. Its DNS name is unique. Its DNS name doesn’t change. Its DNS name is in some way useful for networking. Some of these may be true in some specific circumstances, but none of them are true in all circumstances. These issues are not unique to Apple platforms — if you look at the Posix spec for gethostname, it says nothing about DNS! — but folks tend to notice these problems more on Apple platforms because Apple devices are often deployed to highly dynamic network environments. So, before you start using the APIs discussed in this post, think carefully about your assumptions. And if you actually do want to work with DNS, there are two cases to consider: If you’re looking for the local host name, use the APIs discussed above. In other cases, it’s likely that the APIs in this post will not be helpful and you’d be better off focusing on DNS APIs [1]. [1] The API I recommend for this is DNS-SD. See the DNS section in TN3151 Choosing the right networking API. macOS To get the user-assigned device name, call the SCDynamicStoreCopyComputerName(_:_:) function. For example: let userAssignedDeviceName = SCDynamicStoreCopyComputerName(nil, nil) as String? To get the local host name, call the SCDynamicStoreCopyLocalHostName(_:) function. For example: let localHostName = SCDynamicStoreCopyLocalHostName(nil) as String? IMPORTANT This returns just the name label. To form a local host name, append .local.. Both routines return an optional result; code defensively! If you’re displaying these values to the user, use the System Configuration framework dynamic store notification mechanism to keep your UI up to date. iOS and Friends On iOS, iPadOS, tvOS, and visionOS, get the user-assigned device name from the name property on UIDevice. IMPORTANT Access to this is now restricted. For more on that, see the documentation for the com.apple.developer.device-information.user-assigned-device-name entitlement. There is no direct mechanism to get the local host name. Other APIs There are a wide variety of other APIs that purport to return the host name. These include: gethostname The name property on NSHost [1] The hostName property on NSProcessInfo (ProcessInfo in Swift) These are problematic for a number of reasons: They have a complex implementation that makes it hard to predict what value you’ll get back. They might end up trying to infer the host name from the network environment. The existing behaviour is hard to change due to compatibility concerns. Some of them are marked as to-be-deprecated. IMPORTANT The second issue is particularly problematic, because it involves synchronous DNS requests [2]. That’s slow in general. Worse yet, if the network environment is restricted in some way, these calls can be very slow, taking about 30 seconds to time out. Given these problems, it’s generally best to avoid calling these routines at all. [1] It also has a names property, which is a little closer to reality but still not particularly useful. [2] Actually, that’s not true for gethostname. Rather, that call just returns whatever was last set by sethostname. This is always fast. The System Configuration framework infrastructure calls sethostname to update the host name as the system state changes.

Hello Apple Support Team, We are seeing a production crash on iOS 26 devices that appears to originate from Apple system frameworks rather than application code. Crash Summary Crash signature: _xzm_xzone_malloc_freelist_outlined Crashed thread: com.apple.network.connections Frameworks involved: CFNetwork, Security, libdispatch, libsystem_malloc Affected OS: iOS 26.x App built with: Xcode 16 Devices: Multiple models (not device-specific) Reproducibility: Intermittent, higher frequency during app launch / background networking Observed Stack Trace (top frames) _xzm_xzone_malloc_freelist_outlined dispatch_data_create_alloc xpc_data_deserialize SecTrustEvaluateIfNecessary CFNetwork HTTPProtocol / HTTP3Connection com.apple.network.connections App Context The app uses URLSession for networking. Multiple third-party SDKs are integrated (Firebase Analytics, Dynatrace, Appsflyer, and similar analytics/monitoring SDKs). These SDKs perform concurrent background network requests, especially during app launch and foreground transitions. No unsafe memory operations (manual malloc/free, unsafe pointers, or custom networking stacks) are used in the app code. Key Observations The crash is predominantly observed on iOS 26 and not on earlier iOS versions. Stack traces do not include application symbols. Disabling or delaying analytics SDK initialization significantly reduces the crash rate. Reducing concurrent network requests and limiting HTTP/3 usage also mitigates the issue. This suggests a potential regression in CFNetwork / Network.framework / HTTP/3 handling combined with the new memory allocator (xzone) on iOS 26. Impact Random app termination during background networking. Occurs without a clear deterministic repro path, making it difficult to fully mitigate at the app level. Request Could you please help investigate whether this is a known iOS 26 issue related to: HTTP/3 / QUIC networking XPC deserialization Memory allocation in the new xzone allocator High-concurrency network requests We would appreciate guidance on: Recommended mitigations Whether this issue is already tracked internally Any best practices for apps integrating multiple analytics SDKs on iOS 26 Crash logs and additional diagnostics can be provided if needed. Thank you for your support. Best regards, Dhananjay

I'm developing an application using the accessory setup kit (BLE) on iOS 18+. An important aspect of the connection process is being able to find and choose the correct device. I noticed on iOS 18.2 that I was able to both scroll through the discovered accessories as well as view the advertised name. However, after upgrading to 18.7.2, only a single device is viewable and the advertised name is no longer available. Is there a trigger for this feature that I need to enable or was this "multiple discovery" feature removed? If so, why?

On "Accessory Interface Specification CarPlay Addendum R10", it says that it is recommended that the accessory uses a MIMO (2x2) hardware configuration, does this imply that WiFi 5 and SISO (1X1) will be phased out in the near future? When will WiFi 6 MIMO (2x2) become mandatory? On "Accessory Interface Specification CarPlay Addendum R10", it says that Spatial Audio is mandatory. However, for aftermarket in-vehicle infotainment (IVI) system due to the number of speakers are less than 6, is it allowed not to support spatial audio for this type of aftermarket IVI system?

Hello, Our app uses Network Extension / Packet Tunnel Provider to establish VPN connections on macOS and iOS. We have observed that after creating a utun device and adding any IPv4 routes (NEPacketTunnelNetworkSettings.IPv4Settings), the OS automatically adds several host routes via utun to services such as Akamai, Apple Push, etc. These routes appear to correspond to TCP flows that were active at the moment the VPN connection was established. When a particular TCP flow ends, the corresponding host route is deleted. We understand this is likely intended to avoid breaking existing TCP connections. However, we find the behavior of migrating existing TCP flows to the new utun interface simply because any IPv4 route is added somewhat questionable. This approach would make sense in a "full-tunnel" scenario — for example, when all IPv4 traffic (e.g., 0.0.0.0/0) is routed through the tunnel — but not necessarily in a "split-tunnel" configuration where only specific IPv4 routes are added. Is there any way to control or influence this behavior? Would it be possible for FlowDivert to differentiate between full-tunnel and split-tunnel cases, and only preserve existing TCP flows via utun in the full-tunnel scenario? Thank you.

Hello, How long does it usually take for a URL Filter request to be reviewed? It's been 2.5 weeks since we submitted the request form but we haven't received any feedback yet. Just in case, the request ID is D3633USVZZ

For important background information, read Extra-ordinary Networking before reading this. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Working with a Wi-Fi Accessory Building an app that works with a Wi-Fi accessory presents specific challenges. This post discusses those challenges and some recommendations for how to address them. Note While my focus here is iOS, much of the info in this post applies to all Apple platforms. IMPORTANT iOS 18 introduced AccessorySetupKit, a framework to simplify the discovery and configuration of an accessory. I’m not fully up to speed on that framework myself, but I encourage you to watch WWDC 2024 Session 10203 Meet AccessorySetupKit and read the framework documentation. IMPORTANT iOS 26 introduced WiFiAware, a framework for setting up communication with Wi-Fi Aware accessories. Wi-Fi Aware is an industry standard to securely discover, pair, and communicate with nearby devices. This is especially useful for stand-alone accessories (defined below). For more on this framework, watch WWDC 2025 Session 228 Supercharge device connectivity with Wi-Fi Aware and read the framework documentation. For information on how to create a Wi-Fi Aware accessory that works with iPhone, go to Developer > Accessories, download Accessory Design Guidelines for Apple Devices, and review the Wi-Fi Aware chapter. Accessory Categories I classify Wi-Fi accessories into three different categories. A bound accessory is ultimately intended to join the user’s Wi-Fi network. It may publish its own Wi-Fi network during the setup process, but the goal of that process is to get the accessory on to the existing network. Once that’s done, your app interacts with the accessory using ordinary networking APIs. An example of a bound accessory is a Wi-Fi capable printer. A stand-alone accessory publishes a Wi-Fi network at all times. An iOS device joins that network so that your app can interact with it. The accessory never provides access to the wider Internet. An example of a stand-alone accessory is a video camera that users take with them into the field. You might want to write an app that joins the camera’s network and downloads footage from it. A gateway accessory is one that publishes a Wi-Fi network that provides access to the wider Internet. Your app might need to interact with the accessory during the setup process, but after that it’s useful as is. An example of this is a Wi-Fi to WWAN gateway. Not all accessories fall neatly into these categories. Indeed, some accessories might fit into multiple categories, or transition between categories. Still, I’ve found these categories to be helpful when discussing various accessory integration challenges. Do You Control the Firmware? The key question here is Do you control the accessory’s firmware? If so, you have a bunch of extra options that will make your life easier. If not, you have to adapt to whatever the accessory’s current firmware does. Simple Improvements If you do control the firmware, I strongly encourage you to: Support IPv6 Implement Bonjour [1] These two things are quite easy to do — most embedded platforms support them directly, so it’s just a question of turning them on — and they will make your life significantly easier: Link-local addresses are intrinsic to IPv6, and IPv6 is intrinsic to Apple platforms. If your accessory supports IPv6, you’ll always be able to communicate with it, regardless of how messed up the IPv4 configuration gets. Similarly, if you support Bonjour, you’ll always be able to find your accessory on the network. [1] Bonjour is an Apple term for three Internet standards: RFC 3927 Dynamic Configuration of IPv4 Link-Local Addresses RFC 6762 Multicast DNS RFC 6763 DNS-Based Service Discovery WAC For a bound accessory, support Wireless Accessory Configuration (WAC). This is a relatively big ask — supporting WAC requires you to join the MFi Program — but it has some huge benefits: You don’t need to write an app to configure your accessory. The user will be able to do it directly from Settings. If you do write an app, you can use the EAWiFiUnconfiguredAccessoryBrowser class to simplify your configuration process. HomeKit For a bound accessory that works in the user’s home, consider supporting HomeKit. This yields the same onboarding benefits as WAC, and many other benefits as well. Also, you can get started with the HomeKit Open Source Accessory Development Kit (ADK). Bluetooth LE If your accessory supports Bluetooth LE, think about how you can use that to improve your app’s user experience. For an example of that, see SSID Scanning, below. Claiming the Default Route, Or Not? If your accessory publishes a Wi-Fi network, a key design decision is whether to stand up enough infrastructure for an iOS device to make it the default route. IMPORTANT To learn more about how iOS makes the decision to switch the default route, see The iOS Wi-Fi Lifecycle and Network Interface Concepts. This decision has significant implications. If the accessory’s network becomes the default route, most network connections from iOS will be routed to your accessory. If it doesn’t provide a path to the wider Internet, those connections will fail. That includes connections made by your own app. Note It’s possible to get around this by forcing your network connections to run over WWAN. See Binding to an Interface in Network Interface Techniques and Running an HTTP Request over WWAN. Of course, this only works if the user has WWAN. It won’t help most iPad users, for example. OTOH, if your accessory’s network doesn’t become the default route, you’ll see other issues. iOS will not auto-join such a network so, if the user locks their device, they’ll have to manually join the network again. In my experience a lot of accessories choose to become the default route in situations where they shouldn’t. For example, a bound accessory is never going to be able to provide a path to the wider Internet so it probably shouldn’t become the default route. However, there are cases where it absolutely makes sense, the most obvious being that of a gateway accessory. Acting as a Captive Network, or Not? If your accessory becomes the default route you must then decide whether to act like a captive network or not. IMPORTANT To learn more about how iOS determines whether a network is captive, see The iOS Wi-Fi Lifecycle. For bound and stand-alone accessories, becoming a captive network is generally a bad idea. When the user joins your network, the captive network UI comes up and they have to successfully complete it to stay on the network. If they cancel out, iOS will leave the network. That makes it hard for the user to run your app while their iOS device is on your accessory’s network. In contrast, it’s more reasonable for a gateway accessory to act as a captive network. SSID Scanning Many developers think that TN3111 iOS Wi-Fi API overview is lying when it says: iOS does not have a general-purpose API for Wi-Fi scanning It is not. Many developers think that the Hotspot Helper API is a panacea that will fix all their Wi-Fi accessory integration issues, if only they could get the entitlement to use it. It will not. Note this comment in the official docs: NEHotspotHelper is only useful for hotspot integration. There are both technical and business restrictions that prevent it from being used for other tasks, such as accessory integration or Wi-Fi based location. Even if you had the entitlement you would run into these technical restrictions. The API was specifically designed to support hotspot navigation — in this context hotspots are “Wi-Fi networks where the user must interact with the network to gain access to the wider Internet” — and it does not give you access to on-demand real-time Wi-Fi scan results. Many developers look at another developer’s app, see that it’s displaying real-time Wi-Fi scan results, and think there’s some special deal with Apple that’ll make that work. There is not. In reality, Wi-Fi accessory developers have come up with a variety of creative approaches for this, including: If you have a bound accessory, you might add WAC support, which makes this whole issue go away. In many cases, you can avoid the need for Wi-Fi scan results by adopting AccessorySetupKit. You might build your accessory with a barcode containing the info required to join its network, and scan that from your app. This is the premise behind the Configuring a Wi-Fi Accessory to Join the User’s Network sample code. You might configure all your accessories to have a common SSID prefix, and then take advantage of the prefix support in NEHotspotConfigurationManager. See Programmatically Joining a Network, below. You might have your app talk to your accessory via some other means, like Bluetooth LE, and have the accessory scan for Wi-Fi networks and return the results. Programmatically Joining a Network Network Extension framework has an API, NEHotspotConfigurationManager, to programmatically join a network, either temporarily or as a known network that supports auto-join. For the details, see Wi-Fi Configuration. One feature that’s particularly useful is it’s prefix support, allowing you to create a configuration that’ll join any network with a specific prefix. See the init(ssidPrefix:) initialiser for the details. For examples of how to use this API, see: Configuring a Wi-Fi Accessory to Join the User’s Network — It shows all the steps for one approach for getting a non-WAC bound accessory on to the user’s network. NEHotspotConfiguration Sample — Use this to explore the API in general. Secure Communication Users expect all network communication to be done securely. For some ideas on how to set up a secure connection to an accessory, see TLS For Accessory Developers. Revision History 2025-11-05 Added a link to the Accessory Design Guidelines for Apple Devices. 2025-06-19 Added a preliminary discussion of Wi-Fi Aware. 2024-09-12 Improved the discussion of AccessorySetupKit. 2024-07-16 Added a preliminary discussion of AccessorySetupKit. 2023-10-11 Added the HomeKit section. Fixed the link in Secure Communication to point to TLS For Accessory Developers. 2023-07-23 First posted.

How often do we see control filter start and stop? I read somewhere that data filter is long lived and control Filter is short lived. When does the operating system kills the control filter process?

This is a topic that’s come up a few times on the forums, so I thought I’d write up a summary of the issues I’m aware of. If you have questions or comments, start a new thread in the App & System Services > Networking subtopic and tag it with Network Extension. That way I’ll be sure to see it go by. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Network Extension Provider Packaging There are two ways to package a network extension provider: App extension ( appex ) System extension ( sysex ) Different provider types support different packaging on different platforms. See TN3134 Network Extension provider deployment for the details. Some providers, most notably packet tunnel providers on macOS, support both appex and sysex packaging. Sysex packaging has a number of advantages: It supports direct distribution, using Developer ID signing. It better matches the networking stack on macOS. An appex is tied to the logged in user, whereas a sysex, and the networking stack itself, is global to the system as a whole. Given that, it generally makes sense to package your Network Extension (NE) provider as a sysex on macOS. If you’re creating a new product that’s fine, but if you have an existing iOS product that you want to bring to macOS, you have to account for the differences brought on by the move to sysex packaging. Similarly, if you have an existing sysex product on macOS that you want to bring to iOS, you have to account for the appex packaging. This post summarises those changes. Keep the following in mind while reading this post: The information here applies to all NE providers that can be packaged as either an appex or a sysex. When this post uses a specific provider type in an example, it’s just an example. Unless otherwise noted, any information about iOS also applies to iPadOS, tvOS, and visionOS. Process Lifecycle With appex packaging, the system typically starts a new process for each instance of your NE provider. For example, with a packet tunnel provider: When the users starts the VPN, the system creates a process and then instantiates and starts the NE provider in that process. When the user stops the VPN, the system stops the NE provider and then terminates the process running it. If the user starts the VPN again, the system creates an entirely new process and instantiates and starts the NE provider in that. In contrast, with sysex packaging there’s typically a single process that runs all off the sysex’s NE providers. Returning to the packet tunnel provider example: When the users starts the VPN, the system instantiates and starts the NE provider in the sysex process. When the user stops the VPN, the system stops and deallocates the NE provider instances, but leaves the sysex process running. If the user starts the VPN again, the system instantiates and starts a new instances of the NE provider in the sysex process. This lifecycle reflects how the system runs the NE provider, which in turn has important consequences on what the NE provider can do: An appex acts like a launchd agent [1], in that it runs in a user context and has access to that user’s state. A sysex is effectively a launchd daemon. It runs in a context that’s global to the system as a whole. It does not have access to any single user’s state. Indeed, there might be no user logged in, or multiple users logged in. The following sections explore some consequences of the NE provider lifecycle. [1] It’s not actually run as a launchd agent. Rather, there’s a system launchd agent that acts as the host for the app extension. App Groups With an app extension, the app extension and its container app run as the same user. Thus it’s trivial to share state between them using an app group container. Note When talking about extensions on Apple platforms, the container app is the app in which the extension is embedded and the host app is the app using the extension. For network extensions the host app is the system itself. That’s not the case with a system extension. The system extension runs as root whereas the container app runs an the user who launched it. While both programs can claim access to the same app group, the app group container location they receive will be different. For the system extension that location will be inside the home directory for the root user. For the container app the location will be inside the home directory of the user who launched it. This does not mean that app groups are useless in a Network Extension app. App groups are also a factor in communicating between the container app and its extensions, the subject of the next section. IMPORTANT App groups have a long and complex history on macOS. For the full story, see App Groups: macOS vs iOS: Working Towards Harmony. Communicating with Extensions With an app extension there are two communication options: App-provider messages App groups App-provider messages are supported by NE directly. In the container app, send a message to the provider by calling sendProviderMessage(_:responseHandler:) method. In the appex, receive that message by overriding the handleAppMessage(_:completionHandler:) method. An appex can also implement inter-process communication (IPC) using various system IPC primitives. Both the container app and the appex claim access to the app group via the com.apple.security.application-groups entitlement. They can then set up IPC using various APIs, as explain in the documentation for that entitlement. With a system extension the story is very different. App-provider messages are supported, but they are rarely used. Rather, most products use XPC for their communication. In the sysex, publish a named XPC endpoint by setting the NEMachServiceName property in its Info.plist. Listen for XPC connections on that endpoint using the XPC API of your choice. Note For more information about the available XPC APIs, see XPC Resources. In the container app, connect to that named XPC endpoint using the XPC Mach service name API. For example, with NSXPCConnection, initialise the connection with init(machServiceName:options:), passing in the string from NEMachServiceName. To maximise security, set the .privileged flag. Note XPC Resources has a link to a post that explains why this flag is important. If the container app is sandboxed — necessary if you ship on the Mac App Store — then the endpoint name must be prefixed by an app group ID that’s accessible to that app, lest the App Sandbox deny the connection. See the app groups documentation for the specifics. When implementing an XPC listener in your sysex, keep in mind that: Your sysex’s named XPC endpoint is registered in the global namespace. Any process on the system can open a connection to it [1]. Your XPC listener must be prepared for this. If you want to restrict connections to just your container app, see XPC Resources for a link to a post that explains how to do that. Even if you restrict access in that way, it’s still possible for multiple instances of your container app to be running simultaneously, each with its own connection to your sysex. This happens, for example, if there are multiple GUI users logged in and different users run your container app. Design your XPC protocol with this in mind. Your sysex only gets one named XPC endpoint, and thus one XPC listener. If your sysex includes multiple NE providers, take that into account when you design your XPC protocol. [1] Assuming that connection isn’t blocked by some other mechanism, like the App Sandbox. Inter-provider Communication A sysex can include multiple types of NE providers. For example, a single sysex might include a content filter and a DNS proxy provider. In that case the system instantiates all of the NE providers in the same sysex process. These instances can communicate without using IPC, for example, by storing shared state in global variables (with suitable locking, of course). It’s also possible for a single container app to contain multiple sysexen, each including a single NE provider. In that case the system instantiates the NE providers in separate processes, one for each sysex. If these providers need to communicate, they have to use IPC. In the appex case, the system instantiates each provider in its own process. If two providers need to communicate, they have to use IPC. Managing Secrets An appex runs in a user context and thus can store secrets, like VPN credentials, in the keychain. On macOS this includes both the data protection keychain and the file-based keychain. It can also use a keychain access group to share secrets with its container app. See Sharing access to keychain items among a collection of apps. Note If you’re not familiar with the different types of keychain available on macOS, see TN3137 On Mac keychain APIs and implementations. A sysex runs in the global context and thus doesn’t have access to user state. It also doesn’t have access to the data protection keychain. It must use the file-based keychain, and specifically the System keychain. That means there’s no good way to share secrets with the container app. Instead, do all your keychain operations in the sysex. If the container app needs to work with a secret, have it pass that request to the sysex via IPC. For example, if the user wants to use a digital identity as a VPN credential, have the container app get the PKCS#12 data and password and then pass that to the sysex so that it can import the digital identity into the keychain. Memory Limits iOS imposes strict memory limits an NE provider appexen [1]. macOS imposes no memory limits on NE provider appexen or sysexen. [1] While these limits are not documented officially, you can get a rough handle on the current limits by reading the posts in this thread. Frameworks If you want to share code between a Mac app and its embedded appex, use a structure like this: MyApp.app/ Contents/ MacOS/ MyApp PlugIns/ MyExtension.appex/ Contents/ MacOS/ MyExtension … Frameworks/ MyFramework.framework/ … There’s one copy of the framework, in the app’s Frameworks directory, and both the app and the appex reference it. This approach works for an appex because the system always loads the appex from your app’s bundle. It does not work for a sysex. When you activate a sysex, the system copies it to a protected location. If that sysex references a framework in its container app, it will fail to start because that framework isn’t copied along with the sysex. The solution is to structure your app like this: MyApp.app/ Contents/ MacOS/ MyApp Library/ SystemExtensions/ MyExtension.systemextension/ Contents/ MacOS/ MyExtension Frameworks/ MyFramework.framework/ … … That is, have both the app and the sysex load the framework from the sysex’s Frameworks directory. When the system copies the sysex to its protected location, it’ll also copy the framework, allowing the sysex to load it. To make this work you have to change the default rpath configuration set up by Xcode. Read Dynamic Library Standard Setup for Apps to learn how that works and then tweak things so that: The framework is embedded in the sysex, not the container app. The container app has an additional LC_RPATH load command for the sysex’s Frameworks directory (@executable_path/../Library/SystemExtensions/MyExtension.systemextension/Contents/Frameworks). The sysex’s LC_RPATH load command doesn’t reference the container app’s Frameworks directory (@executable_path/../../../../Frameworks) but instead points to the sysex’s Framweorks directory (@executable_path/../Frameworks). Entitlements When you build an app with an embedded NE extension, both the app and the extension must be signed with the com.apple.developer.networking.networkextension entitlement. This is a restricted entitlement, that is, it must be authorised by a provisioning profile. The value of this entitlement is an array, and the values in that array differ depend on your distribution channel: If you distribute your app directly with Developer ID signing, use the values with the -systemextension suffix. Otherwise — including when you distribute the app on the App Store and when signing for development — use the values without that suffix. Make sure you authorise these values with your provisioning profile. If, for example, you use an App Store distribution profile with a Developer ID signed app, things won’t work because the profile doesn’t authorise the right values. In general, the easiest option is to use Xcode’s automatic code signing. However, watch out for the pitfall described in Exporting a Developer ID Network Extension. Revision History 2025-11-06 Added the Entitlements section. Explained that, with sysex packaging, multiple instances of your container app might connect simultaneously with your sysex. 2025-09-17 First posted.

My external device can generate a fixed Wi-Fi network. When I connect to this Wi-Fi using my iPhone 17 Pro Max (iOS version 26.0.1), and my app tries to establish a connection using the following method, this method returns -1 int connect(int, const struct sockaddr *, socklen_t) __DARWIN_ALIAS_C(connect); However, when I use other phones, such as iPhone 12, iPhone 8, iPhone 11, etc., to connect to this external device, the above method always returns successfully, with the parameters passed to the method remaining the same. I also tried resetting the network settings on the iPhone 17 Pro Max (iOS version 26.0.1), but it still cannot establish a connection.

Starting in iOS 26, two notable changes have been made to CallKit, LiveCommunicationKit, and the PushToTalk framework: As a diagnostic aid, we're introducing new dialogs to warn apps of voip push related issue, for example when they fail to report a call or when when voip push delivery stops. The specific details of that behavior are still being determined and are likely to change over time, however, the critical point here is that these alerts are only intended to help developers debug and improve their app. Because of that, they're specifically tied to development and TestFlight signed builds, so the alert dialogs will not appear for customers running app store builds. The existing termination/crashes will still occur, but the new warning alerts will not appear. As PushToTalk developers have previously been warned, the last unrestricted PushKit entitlement ("com.apple.developer.pushkit.unrestricted-voip.ptt") has been disabled in the iOS 26 SDK. ALL apps that link against the iOS 26 SDK which receive a voip push through PushKit and which fail to report a call to CallKit will be now be terminated by the system, as the API contract has long specified. __ Kevin Elliott DTS Engineer, CoreOS/Hardware

Is this even possible? Instead of any pairing dialog appearing, my central code get the "Authentication is insufficient" error when reading the characteristic. My peripheral (in the macOS app) code uses the .notifyEncryptionRequired property and uses .readEncryptionRequired and .writeEncryptionRequired permissions. No descriptors are set, but I think they get added automatically since this characteristic notifies. 2900 and 2902 descriptors are set by the peripheral/CoreBluetooth. If the Mac and iPhone are using the same Apple ID does that affect pairing?

Is Apple's Wi-Fi Aware certified by the Wi-Fi Alliance? Is there any non-compliance of Apple's Wi-Fi Aware with the Wi-Fi Alliance standards? Does Apple have a roadmap to switch AWDL to Wi-Fi Aware? Does Apple have plans to adopt Wi-Fi Aware in Mac computers?

Hi there, We’re developing a companion app for a smart home product that communicates over the user’s local network. To provision the device, it initially creates its own Wi-Fi network. The user joins this temporary network and enters their home Wi-Fi credentials via our app. The app then sends those credentials directly to the device, which stores them and connects to the local network for normal operation. We’re using AccessorySetupKit to discover nearby devices (via SSID prefix) and NEHotspotManager to join the accessory’s Wi-Fi network once the user selects it. This workflow works well in general. However, we’ve encountered a problem: if the user factory-resets the accessory, or needs to restart setup (for example, after entering the wrong Wi-Fi password), the device no longer appears in the accessory picker. In iOS 18, we were able to work around this by calling removeAccessory() after the device is selected. This forces the picker to always display the accessory again. But in iOS 26, a new confirmation dialog now appears when calling removeAccessory(), which confuses users during setup. We’re looking for a cleaner way to handle this scenario — ideally a way to make the accessory rediscoverable without prompting the user to confirm removal. Thanks for your time and guidance.

This issue has cropped up many times here on DevForums. Someone recently opened a DTS tech support incident about it, and I used that as an opportunity to post a definitive response here. If you have questions or comments about this, start a new thread and tag it with Network so that I see it. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" iOS Network Signal Strength The iOS SDK has no general-purpose API that returns Wi-Fi or cellular signal strength in real time. Given that this has been the case for more than 10 years, it’s safe to assume that it’s not an accidental omission but a deliberate design choice. For information about the Wi-Fi APIs that are available on iOS, see TN3111 iOS Wi-Fi API overview. Network performance Most folks who ask about this are trying to use the signal strength to estimate network performance. This is a technique that I specifically recommend against. That’s because it produces both false positives and false negatives: The network signal might be weak and yet your app has excellent connectivity. For example, an iOS device on stage at WWDC might have terrible WWAN and Wi-Fi signal but that doesn’t matter because it’s connected to the Ethernet. The network signal might be strong and yet your app has very poor connectivity. For example, if you’re on a train, Wi-Fi signal might be strong in each carriage but the overall connection to the Internet is poor because it’s provided by a single over-stretched WWAN. The only good way to determine whether connectivity is good is to run a network request and see how it performs. If you’re issuing a lot of requests, use the performance of those requests to build a running estimate of how well the network is doing. Indeed, Apple practices what we preach here: This is exactly how HTTP Live Streaming works. Remember that network performance can change from moment to moment. The user’s train might enter or leave a tunnel, the user might step into a lift, and so on. If you build code to estimate the network performance, make sure it reacts to such changes. Keeping all of the above in mind, iOS 26 beta has two new APIs related to this issue: Network framework now offers a linkQuality property. See this post for my take on how to use this effectively. The WirelessInsights framework can notify you of anticipated WWAN condition changes. But what about this code I found on the ’net? Over the years various folks have used various unsupported techniques to get around this limitation. If you find code on the ’net that, say, uses KVC to read undocumented properties, or grovels through system logs, or walks the view hierarchy of the status bar, don’t use it. Such techniques are unsupported and, assuming they haven’t broken yet, are likely to break in the future. But what about Hotspot Helper? Hotspot Helper does have an API to read Wi-Fi signal strength, namely, the signalStrength property. However, this is not a general-purpose API. Like the rest of Hotspot Helper, this is tied to the specific use case for which it was designed. This value only updates in real time for networks that your hotspot helper is managing, as indicated by the isChosenHelper property. But what about MetricKit? MetricKit is so cool. Amongst other things, it supports the MXCellularConditionMetric payload, which holds a summary of the cellular conditions while your app was running. However, this is not a real-time signal strength value. But what if I’m working for a carrier? This post is about APIs in the iOS SDK. If you’re working for a carrier, discuss your requirements with your carrier’s contact at Apple. Revision History 2025-07-02 Updated to cover new features in the iOS 16 beta. Made other minor editorial changes. 2022-12-01 First posted.

I've been able to run this sample project with the PIRServer. But the urls are still not blocked. https://developer.apple.com/documentation/networkextension/filtering-traffic-by-url https://github.com/apple/pir-service-example I got this on the log Received filter status change: <FilterStatus: 'running'>

At WWDC 2015 Apple announced two major enhancements to the Network Extension framework: Network Extension providers — These are app extensions that let you insert your code at various points within the networking stack, including: Packet tunnels via NEPacketTunnelProvider App proxies via NEAppProxyProvider Content filters via NEFilterDataProvider and NEFilterControlProvider Hotspot Helper (NEHotspotHelper) — This allows you to create an app that assists the user in navigating a hotspot (a Wi-Fi network where the user must interact with the network in order to get access to the wider Internet). Originally, using any of these facilities required authorisation from Apple. Specifically, you had to apply for, and be granted access to, a managed capability. In Nov 2016 this policy changed for Network Extension providers. Any developer can now use the Network Extension provider capability like they would any other capability. There is one exception to this rule: Network Extension app push providers, introduced by iOS 14 in 2020, still requires that Apple authorise the use of a managed capability. To apply for that, follow the link in Local push connectivity. Also, the situation with Hotspot Helpers remains the same: Using a Hotspot Helper, requires that Apple authorise that use via a managed capability. To apply for that, follow the link in Hotspot helper. IMPORTANT Pay attention to this quote from the documentation: NEHotspotHelper is only useful for hotspot integration. There are both technical and business restrictions that prevent it from being used for other tasks, such as accessory integration or Wi-Fi based location. The rest of this document answers some frequently asked questions about the Nov 2016 change. #1 — Has there been any change to the OS itself? No, this change only affects the process by which you get the capabilities you need in order to use existing Network Extension framework facilities. Previously these were managed capabilities, meaning their use was authorised by Apple. Now, except for app push providers and Hotspot Helper, you can enable the necessary capabilities using Xcode’s Signing & Capabilities editor or the Developer website. IMPORTANT Some Network Extension providers have other restrictions on their use. For example, a content filter can only be used on a supervised device. These restrictions are unchanged. See TN3134 Network Extension provider deployment for the details. #2 — How exactly do I enable the Network Extension provider capability? In the Signing & Capabilities editor, add the Network Extensions capability and then check the box that matches the provider you’re creating. In the Certificates, Identifiers & Profiles section of the Developer website, when you add or edit an App ID, you’ll see a new capability listed, Network Extensions. Enable that capability in your App ID and then regenerate the provisioning profiles based on that App ID. A newly generated profile will include the com.apple.developer.networking.networkextension entitlement in its allowlist; this is an array with an entry for each of the supported Network Extension providers. To confirm that this is present, dump the profile as shown below. $ security cms -D -i NETest.mobileprovision … <plist version="1.0"> <dict> … <key>Entitlements</key> <dict> <key>com.apple.developer.networking.networkextension</key> <array> <string>packet-tunnel-provider</string> <string>content-filter-provider</string> <string>app-proxy-provider</string> … and so on … </array> … </dict> … </dict> </plist> #3 — I normally use Xcode’s Signing & Capabilities editor to manage my entitlements. Do I have to use the Developer website for this? No. Xcode 11 and later support this capability in the Signing & Capabilities tab of the target editor (r. 28568128 ). #4 — Can I still use Xcode’s “Automatically manage signing” option? Yes. Once you modify your App ID to add the Network Extension provider capability, Xcode’s automatic code signing support will include the entitlement in the allowlist of any profiles that it generates based on that App ID. #5 — What should I do if I previously applied for the Network Extension provider managed capability and I’m still waiting for a reply? Consider your current application cancelled, and use the new process described above. #6 — What should I do if I previously applied for the Hotspot Helper managed capability and I’m still waiting for a reply? Apple will continue to process Hotspot Helper managed capability requests and respond to you in due course. #7 — What if I previously applied for both Network Extension provider and Hotspot Helper managed capabilities? Apple will ignore your request for the Network Extension provider managed capability and process it as if you’d only asked for the Hotspot Helper managed capability. #8 — On the Mac, can Developer ID apps host Network Extension providers? Yes, but there are some caveats: This only works on macOS 10.15 or later. Your Network Extension provider must be packaged as a system extension, not an app extension. You must use the *-systemextension values for the Network Extension entitlement (com.apple.developer.networking.networkextension). For more on this, see Exporting a Developer ID Network Extension. #9 — After moving to the new process, my app no longer has access to the com.apple.managed.vpn.shared keychain access group. How can I regain that access? Access to this keychain access group requires another managed capability. If you need that, please open a DTS code-level support request and we’ll take things from there. IMPORTANT This capability is only necessary if your VPN supports configuration via a configuration profile and needs to access credentials from that profile (as discussed in the Profile Configuration section of the NETunnelProviderManager Reference). Many VPN apps don’t need this facility. If you were previously granted the Network Extension managed capability (via the process in place before Nov 2016), make sure you mention that; restoring your access to the com.apple.managed.vpn.shared keychain access group should be straightforward in that case. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Revision History 2025-11-11 Removed the discussion of TSI assets because those are no longer a thing. 2025-09-12 Adopted the code-level support request terminology. Made other minor editorial changes. 2023-01-11 Added a discussion of Network Extension app push providers. Added a link to Exporting a Developer ID Network Extension. Added a link to TN3134. Made significant editorial changes. 2020-02-27 Fixed the formatting. Updated FAQ#3. Made minor editorial changes. 2020-02-16 Updated FAQ#8 to account for recent changes. Updated FAQ#3 to account for recent Xcode changes. Made other editorial changes. 2016-01-25 Added FAQ#9. 2016-01-6 Added FAQ#8. 2016-11-11 Added FAQ#5, FAQ#6 and FAQ#7. 2016-11-11 First posted.

The path from Network Extension’s in-provider networking APIs to Network framework has been long and somewhat rocky. The most common cause of confusion is NWEndpoint, where the same name can refer to two completely different types. I’ve helped a bunch of folks with this over the years, and I’ve decided to create this post to collect together all of those titbits. If you have questions or comments, please put them in a new thread. Put it in the App & System Services > Networking subtopic and tag it with Network Extension. That way I’ll be sure to see it go by. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" NWEndpoint History and Advice A tale that spans three APIs, two languages, and ten years. The NWEndpoint type has a long and complex history, and if you’re not aware of that history you can bump into weird problems. The goal of this post is to explain the history and then offer advice on how to get around specific problems. IMPORTANT This post focuses on NWEndpoint, because that’s the type that causes the most problems, but there’s a similar situation with NWPath. The History In iOS 9 Apple introduced the Network Extension (NE) framework, which offers a convenient way for developers to create a custom VPN transport. Network Extension types all have the NE prefix. Note I’m gonna use iOS versions here, just to keep the text simple. If you’re targeting some other platform, use this handy conversion table: iOS | macOS | tvOS | watchOS | visionOS --- + ----- + ---- + ------- + -------- 9 | 10.11 | 9 | 2 | - 12 | 10.14 | 12 | 5 | - 18 | 15 | 18 | 11 | 2 At that time we also introduced in-provider networking APIs. The idea was that an NE provider could uses these Objective-C APIs to communicate with its VPN server, and thereby avoiding a bunch of ugly BSD Sockets code. The in-provider networking APIs were limited to NE providers. Specifically, the APIs to construct an in-provider connection were placed on types that were only usable within an NE provider. For example, a packet tunnel provider could create a NWTCPConnection object by calling -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] and -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate:, which are both methods on NEPacketTunnelProvider. These in-provider networking APIs came with a number of ancillary types, including NWEndpoint and NWPath. At the time we thought that we might promote these in-provider networking APIs to general-purpose networking APIs. That’s why the APIs use the NW prefix. For example, it’s NWTCPConnection, not NETCPConnection. However, plans changed. In iOS 12 Apple shipped Network framework as our recommended general-purpose networking API. This actually includes two APIs: A Swift API that follows Swift conventions, for example, the connection type is called NWConnection A C API that follows C conventions, for example, the connection type is called nw_connection_t These APIs follow similar design patterns to the in-provider networking API, and thus have similar ancillary types. Specifically, there are an NWEndpoint and nw_endpoint_t types, both of which perform a similar role to the NWEndpoint type in the in-provider networking API. This was a source of some confusion in Swift, because the name NWEndpoint could refer to either the Network framework type or the Network Extension framework type, depending on what you’d included. Fortunately you could get around this by qualifying the type as either Network.NWEndpoint or NetworkExtension.NWEndpoint. The arrival of Network framework meant that it no longer made sense to promote the in-provider networking APIs to general-purposes networking APIs. The in-provider networking APIs were on the path to deprecation. However, deprecating these APIs was actually quite tricky. Network Extension framework uses these APIs in a number of interesting ways, and so deprecating them required adding replacements. In addition, we’d needed different replacements for Swift and Objective-C, because Network framework has separate APIs for Swift and C-based languages. In iOS 18 we tackled that problem head on. To continue the NWTCPConnection example above, we replaced: -createTCPConnectionToEndpoint:enableTLS:TLSParameters:delegate:] with nw_connection_t -createTCPConnectionThroughTunnelToEndpoint:enableTLS:TLSParameters:delegate: with nw_connection_t combined with a new virtualInterface property on NEPacketTunnelProvider Of course that’s the Objective-C side of things. In Swift, the replacement is NWConnection rather than nw_connection_t, and the type of the virtualInterface property is NWInterface rather than nw_interface_t. But that’s not the full story. For the two types that use the same name in both frameworks, NWEndpoint and NWPath, we decided to use this opportunity to sort out that confusion. To see how we did that, check out the <NetworkExtension/NetworkExtension.apinotes> file in the SDK. Focusing on NWEndpoint for the moment, you’ll find two entries: … - Name: NWEndpoint SwiftPrivate: true … SwiftVersions: - Version: 5.0 … - Name: NWEndpoint SwiftPrivate: false … The first entry applies when you’re building with the Swift 6 language mode. This marks the type as SwiftPrivate, which means that Swift imports it as __NWEndpoint. That frees up the NWEndpoint name to refer exclusively to the Network framework type. The second entry applies when you’re building with the Swift 5 language mode. It marks the type as not SwiftPrivate. This is a compatible measure to ensure that code written for Swift 5 continues to build. The Advice This sections discusses specific cases in this transition. NWEndpoint and NWPath In Swift 5 language mode, NWEndpoint and NWPath might refer to either framework, depending on what you’ve imported. Add a qualifier if there’s any ambiguity, for example, Network.NWEndpoint or NetworkExtension.NWEndpoint. In Swift 6 language mode, NWEndpoint and NWPath always refer to the Network framework type. Add a __ prefix to get to the Network Extension type. For example, use NWEndpoint for the Network framework type and __NWEndpoint for the Network Extension type. Direct and Through-Tunnel TCP Connections in Swift To create a connection directly, simply create an NWConnection. This support both TCP and UDP, with or without TLS. To create a connection through the tunnel, replace code like this: let c = self.createTCPConnectionThroughTunnel(…) with code like this: let params = NWParameters.tcp params.requiredInterface = self.virtualInterface let c = NWConnection(to: …, using: params) This is for TCP but the same basic process applies to UDP. UDP and App Proxies in Swift If you’re building an app proxy, transparent proxy, or DNS proxy in Swift and need to handle UDP flows using the new API, adopt the NEAppProxyUDPFlowHandling protocol. So, replace code like this: class AppProxyProvider: NEAppProxyProvider { … override func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } with this: class AppProxyProvider: NEAppProxyProvider, NEAppProxyUDPFlowHandling { … func handleNewUDPFlow(_ flow: NEAppProxyUDPFlow, initialRemoteFlowEndpoint remoteEndpoint: NWEndpoint) -> Bool { … } } Creating a Network Rule To create an NWHostEndpoint, replace code like this: let ep = NWHostEndpoint(hostname: "1.2.3.4", port: "12345") let r = NENetworkRule(destinationHost: ep, protocol: .TCP) with this: let ep = NWEndpoint.hostPort(host: "1.2.3.4", port: 12345) let r = NENetworkRule(destinationHostEndpoint: ep, protocol: .TCP) Note how the first label of the initialiser has changed from destinationHost to destinationHostEndpoint.

Every now and again folks notice that Network framework seems to create an unexpected number of connections on the wire. This post explains why that happens and what you should do about it. If you have questions or comments, put them in a new thread here on the forums. Use the App & System Services > Networking topic area and the Network tag. Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" Understanding Also-Ran Connections Network framework implements the Happy Eyeballs algorithm. That might create more on-the-wire connections than you expect. There are two common places where folks notice this: When looking at a packet trace When implementing a listener Imagine that you’ve implemented a TCP server using NWListener and you connect to it from a client using NWConnection. In many situations there are multiple network paths between the client and the server. For example, on a local network there’s always at least two paths: the link-local IPv6 path and either an infrastructure IPv4 path or the link-local IPv4 path. When you start your NWConnection, Network framework’s Happy Eyeballs algorithm might [1] start a TCP connection for each of these paths. It then races those connections. The one that connects first is the ‘winner’, and Network framework uses that connection for your traffic. Once it has a winner, the other connections, the also-ran connections, are redundant, and Network framework just closes them. You can observe this behaviour on the client side by looking in the system log. Many Network framework log entries (subsystem com.apple.network) contain a connection identifier. For example C8 is the eighth connection started by this process. Each connection may have child connections (C8.1, C8.2, …) and grandchild connections (C8.1.1, C8.1.2, …), and so on. You’ll see state transitions for these child connections occurring in parallel. For example, the following log entries show that C8 is racing the connection of two grandchild connections, C8.1.1 and C8.1.2: type: debug time: 12:22:26.825331+0100 process: TestAlsoRanConnections subsystem: com.apple.network category: connection message: nw_socket_connect [C8.1.1:1] Calling connectx(…) type: debug time: 12:22:26.964150+0100 process: TestAlsoRanConnections subsystem: com.apple.network category: connection message: nw_socket_connect [C8.1.2:1] Calling connectx(…) Note For more information about accessing the system log, see Your Friend the System Log. You also see this on the server side, but in this case each connection is visible to your code. When you connect from the client, Network framework calls your listener’s new connection handler with multiple connections. One of those is the winning connection and you’ll receive traffic on it. The others are the also-ran connections, and they close promptly. IMPORTANT Depending on network conditions there may be no also-ran connections. Or there may be lots of them. If you want to test the also-ran connection case, use Network Link Conditioner to add a bunch of delay to your packets. You don’t need to write special code to handle also-ran connections. From the perspective of your listener, these are simply connections that open and then immediately close. There’s no difference between an also-ran connection and, say, a connection from a client that immediately crashes. Or a connection generated by someone doing a port scan. Your server must be resilient to such things. However, the presence of these also-ran connections can be confusing, especially if you’re just getting started with Network framework, and hence this post. [1] This is “might” because the exact behaviour depends on network conditions. More on that below.