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Explore the networking protocols and technologies used by the device to connect to Wi-Fi networks, Bluetooth devices, and cellular data services.

Networking Documentation

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Bonjour Conformance Test - Multiple Instance in Single Device
We are currently working on a zero-configuration networking compliant device thru avahi-daemon. Our Device want to have multiple Instance name for different services. Example InstanceA._ipps._tcp.local. InstanceA._ipp._tcp.local. InstanceB._ipps._tcp.local. InstanceB._ipp._tcp.local. Will BCT confuse this as multiple device connected in the network and cause it to fail? Does Bonjour only allows only a Single Instance name with multiple services?
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105
Apr ’25
Do watchOS apps support IP request communication within a local area network?
As a third-party application on Apple Watch, can it be located in the same LAN httpServer? Currently, when testing to initiate an http request in the LAN, the connection timeout is returned, code: -1001 self.customSession.request("http://10.15.48.191:9000/hello").response { response in switch response.result { case .success(let data): dlog("✅ 请求成功,收到数据:") if let html = String(data: data ?? Data(), encoding: .utf8) { dlog(html) } case .failure(let error): dlog("❌ 请求失败:\(error.localizedDescription)") } } 执行后报错 Task <B71BE820-FD0E-4880-A6DD-1F8F6EAF98B0>.<1> finished with error [-1001] Error Domain=NSURLErrorDomain Code=-1001 "请求超时。" UserInfo={_kCFStreamErrorCodeKey=-2102, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <B71BE820-FD0E-4880-A6DD-1F8F6EAF98B0>.<1>, _NSURLErrorRelatedURLSessionTaskErrorKey=( "LocalDataTask <B71BE820-FD0E-4880-A6DD-1F8F6EAF98B0>.<1>", "LocalDataPDTask <B71BE820-FD0E-4880-A6DD-1F8F6EAF98B0>.<1>", "LocalDataTask <B71BE820-FD0E-4880-A6DD-1F8F6EAF98B0>.<1>" ), NSLocalizedDescription=请求超时。, _kCFStreamErrorDomainKey=4, NSErrorFailingURLStringKey=http://10.15.48.191:9000/hello, NSErrorFailingURLKey=http://10.15.48.191:9000/hello}
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129
May ’25
Cellular only VPN app
I have a requirement to create a VPN app which only works on Cellular. But I'm facing an issue like when wifi is ON, OS is using wifi interface to route the traffic instead of cellular. I tried some ways like let cellularParams = NWParameters.udp cellularParams.requiredInterfaceType = .cellular But this is not working properly as expected. How can I manually bind to cellular interface in iOS?
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101
Jul ’25
How to Keep Cellular Data Active While Connected to a Local Hotspot for File Transfer?
Hi all, I’m developing a companion iOS app that connects to a device-created Wi-Fi hotspot to transfer videos or other files WebSocket. The challenge is: once the iPhone connects to this hotspot, it loses internet access because iOS routes all traffic through Wi-Fi. However, I’d like to keep the iPhone’s cellular data active and usable while staying connected to the local hotspot — so the app can access cloud APIs, or the user can continue using other apps that require internet access. I understand that iOS prioritizes Wi-Fi over cellular, but are there any supported workarounds or patterns (e.g., MFi programs, local-only Wi-Fi access, NEHotspotConfiguration behavior, etc.) that : • Using Wi-Fi only for local communication; • cellular to remain active for internet access. Any insights or Apple-recommended best practices would be greatly appreciated — especially any official references regarding MFi Accessory setup or NEHotspotConfiguration behavior in this context. Thanks in !
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109
Jun ’25
iOS Not Sending DHCP Request After Quick WiFi Reconnect
I'm facing an issue where if a WiFi network is turned off and back on within a short time frame (2-4 seconds), iOS still shows the device as connected but does not send a new DHCP request. This causes a problem for my network device, which relies on the DHCP request to assign an IP address. Without the request, the device is unable to establish a socket connection properly. Is there any way to force iOS to send a DHCP request immediately when reconnecting to the network in this scenario? Are there any known workarounds or configurations that might help ensure the DHCP process is re-triggered? Any insights would be appreciated. Thanks!
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229
Mar ’25
How to delete cookies on IOS18
Hello, I have encountered an issue with an iPhone 15PM with iOS 18.5. The NSHTTPCookieStorage failed to clear cookies, but even after clearing them, I was still able to retrieve them. However, on the same system It is normal on iPhone 14PM. I would like to know the specific reason and whether there are any adaptation related issues. Following code: NSHTTPCookie *cookie; NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage]; for (cookie in [storage cookies]) { [storage deleteCookie:cookie]; }
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167
May ’25
in-addr.arpa default search domains
Hi, I observed some unexpected behavior and hope that someone can enlighten me as to what this is about: mDNSResponder prepends IP / network based default search domains that are checked before any other search domain. E.g. 0.1.168.192.in-addr.arpa. would be used for an interface with an address in the the 192.168.1.0/24 subnet. This is done for any configured non-link-local IP address. I tried to find any mention of an approach like this in RFCs but couldn't spot anything. Please note that this is indeed a search domain and different from reverse-DNS lookups. Example output of tcpdump for ping devtest: 10:02:13.850802 IP (tos 0x0, ttl 64, id 43461, offset 0, flags [none], proto UDP (17), length 92) 192.168.1.2.52319 &gt; 192.168.1.1.53: 54890+ [1au] A? devtest.0.1.168.192.in-addr.arpa. (64) I was able to identify the code that adds those default IP subnet based search domains but failed to spot any indication as to what this is about: https://github.com/apple-oss-distributions/mDNSResponder/blob/d5029b5/mDNSMacOSX/mDNSMacOSX.c#L4171-L4211 Does anyone here have an ideas as to what this might be about?
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771
Apr ’25
NEPacketTunnelProvider `start/stopTunnel` synchronization
I was having a look through the documentation for NEPacketTunnelProvider, and wanted to know if it's possible for startTunnel(..) and stopTunnel(..) to run simultaneously, and thus require synchronization between resources they deal with? For example, if the VPN is toggled rapidly from system settings, could the setup that occurs in my startTunnel() definition (class instantiation and setTunnelNetworkSettings(value)) potentially occur after the tear-down logic (resource cleanup, setTunnelNetworkSettings(nil)), leaving the system in a state where the VPN is deactivated, but the configuration is in place?
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80
Jul ’25
Macos pf.conf
I have a question regarding /etc/pf.conf. If I use this rule, rdr pass on bridge100 inet proto tcp from 192.168.2.104 to any port {80, 443, 8883} -> 127.0.0.1 port 8080 all other traffic on bridge100 will not function properly, even the traffic that is not destined for 192.168.2.104. Additionally, the hotspot generated through bridge100 will also become unavailable. Even if I comment out this rule and run sudo pfctl -e -f /etc/pf.conf, the problem still persists. The situation will only return to normal when I restart my Mac. my macos:15.3.2 my /etc/pf.conf # scrub-anchor "com.apple/*" nat-anchor "com.apple/*" rdr-anchor "com.apple/*" rdr pass on bridge100 inet proto tcp from 192.168.2.104 to any port {80, 443, 8883} -> 127.0.0.1 port 8080 dummynet-anchor "com.apple/*" anchor "com.apple/*" load anchor "com.apple" from "/etc/pf.anchors/com.apple"
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323
Mar ’25
Enhancing NEFilterPacketProvider with Process-Level Filtering
Our application currently uses NEFilterPacketProvider to filter network traffic based on Layer 4 rules (5-tuple: source IP, destination IP, source port, destination port, and protocol) on a packet-by-packet basis. We now want to extend this filtering to also consider the associated process—for example, allowing traffic from a specific source IP to a destination IP and port only if it's associated with a specific local process. That is, we’d like to make filtering decisions not just based on the 5-tuple, but also on the identity of the process either sending or receiving the traffic. We’ve looked into NEFilterSocketProvider, which does expose Layer 7 information such as process identifiers. However, it doesn’t seem to be tightly synchronized with the packet flow handled by NEFilterPacketProvider. As a result, there’s a risk that we might only get process information after the TCP handshake is complete, or before the socket is fully bound—at which point some of the 5-tuple fields (such as the local port) may still be unavailable. What we need is a way to correlate the 5-tuple with the relevant process name (either sender or receiver) at the time the first packet—e.g., a SYN packet—is about to be sent or received. Is there a recommended way to achieve this kind of early, process-aware filtering using NetworkExtension APIs?
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102
Jun ’25
Multipeer Connectivity stopped working between iPad simulators
We have an iPad application that utilizes Multipeer Connectivity to enable local communication between devices running a copy of our app. Until recently, we were able to test this functionality in the Xcode simulator without any issues. We could easily set up multiple simulators and have them all communicate with each other. However, recently, either due to an upgrade to Xcode or MacOS, this functionality ceased working in the simulator. Surprisingly, it still functions perfectly on physical devices. If we reboot the development computer and launch the simulator immediately after the reboot (without building and sending from Xcode, but running the existing code on the device), the issue resolves. However, the moment we generate a new build and send it to the simulator from Xcode, the multipeer functionality stops working again in the simulator. The simulators won’t reconnect until a reboot of the physical Mac hardware hosting the simulator. We’ve tried the usual troubleshooting steps, such as downgrading Xcode, deleting simulators and recreating them, cleaning the build folder, and deleting derived data, but unfortunately, none of these solutions have worked. The next step is to attempt to use a previous version of MacOS (15.3) and see if that helps, but I’d prefer to avoid this if possible. Does anyone have any obvious suggestions or troubleshooting steps that might help us identify the cause of this issue?
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352
Jun ’25
PolicyDenied on Simulator with Xcode 16 and Network Framework NWBrowser
I'm using Network framework for communication between devices. The first time I instantiate an NWBrowser, it will prompt the user with a popup that says: Allow &lt;app name&gt; to find devices on local networks? The problem is, once I upgraded from Xcode 15.4 to Xcode 16.4, the popup doesn't appear; it says in the debug window: nw_browser_fail_on_dns_error_locked [B1] nw_browser_dns_service_browse_callback failed: PolicyDenied(18,446,744,073,709,486,046) I do have the info.plist keys Privacy-Local Network Usage Description (NSLocalNetworkUsageDescription) and Bonjour Services (NSBonjourServices) so it's not that. Also, It still works on a real device. I think something changed with Xcode 16 that tightened the security on a simulator, or maybe disabled Network framework entirely. It's not the firewall on my computer because that is turned off. I'm using an M1 MacBook Pro.
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156
Jun ’25
Performance Concerns and Dynamic Control of Parallel Image Uploads Using Swift TaskGroup
I'm currently developing an iOS app with image upload functionality. To enhance upload speed, I'm considering implementing parallel uploads using Swift’s TaskGroup. However, I have concerns that in environments with limited bandwidth, parallelization might introduce overhead and contention, ultimately slowing down uploads instead of improving them. Specifically, I'm curious about: Is this concern valid? Does parallelizing uploads become counterproductive in low-bandwidth conditions due to overhead and network contention? If so, I'm considering dynamically adjusting the concurrency level based on network conditions. Does anyone have experience or best practices regarding such an approach? Any insights or advice would be greatly appreciated. Thank you!
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166
Jun ’25
Unable to update app with PacketTunnelProvider running
Hi there, I am working on an app that configures a PacketTunnelProvider to establish a VPN connection. Unfortunately, while a VPN connection is established, I am unable to update the app via testflight. Downloading other app updates works fine. I noticed that after I receive the alert that updating failed, the vpn badge appears at the top of my screen (the same ux that occurs when the connection is first established). So it's almost like it tried to close the tunnel, and seeing that the app update failed it restablishes the tunnel. I am unsure of why I would not be able to update my app. Maybe stopTunnel is not being called with NEProviderStopReason.appUpdate?
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62
Jun ’25
Upgrading NEFilterDataProvider Causes System Network Interruption
Hi, when I perform an overlay installation via a PKG on macOS for an application containing the NEFilterDataProvider functionality, there is a chance that the entire system network becomes unreachable. Disabling the corresponding Content Filter in "System Settings > Network > Filters" immediately restores network connectivity. This issue does not occur every time, with a frequency of approximately 1 in 20 installation attempts.  The following details may help identify the problem: The Filter.app containing the NEFilterDataProvider resides within the main app's Resources directory, e.g., /Applications/Main.app/Contents/Resources/Filter.app Main.app is installed via a PKG; the issue typically occurs during an overlay installation of Main.app. The NEFilterDataProvider operates as a System Extension. The func handleNewFlow(_ flow: NEFilterFlow) -> NEFilterNewFlowVerdict {} returns .allow. Wireshark packet captures show TCP packets but no UDP packets; TCP handshakes cannot complete. Disabling the corresponding content filter in "System Settings > Network > Filters" restores the network; re-enabling it breaks connectivity again. After waiting for a period, approximately 30-60 minutes, network connectivity can recover automatically. What causes this and how can it be fixed? Any workarounds?
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149
Oct ’25
How to keep API requests running in background using URLSession in Swift?
I'm developing an iOS application in Swift that performs API calls using URLSession.shared. The requests work correctly when the app is in the foreground. However, when the app transitions to the background (for example, when the user switches to another app), the ongoing API calls are either paused or do not complete as expected. What I’ve tried: Using URLSession.shared.dataTask(with:) to initiate the API requests Observing application lifecycle events like applicationDidEnterBackground, but haven't found a reliable solution to allow requests to complete when backgrounded Goal: I want certain API requests to continue running or be allowed to complete even if the app enters the background. Question: What is the correct approach to allow API calls to continue running or complete when the app moves to the background? Should I be using a background URLSessionConfiguration instead of URLSession.shared? If so, how should it be properly configured and used in this scenario?
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204
Oct ’25
Capturing NWConnection in Receive Closure – Risk of Strong Reference Cycle?
Hi Everyone, I have a query regarding capturing an NWConnection instance inside the receive closure, which gets invoked whenever some raw bytes are received. I want to know whether this will create a strong retain cycle or not. My understanding is that NWConnection holds a reference to the closure, and if I capture the NWConnection instance inside the closure, the closure will have a reference back to the connection, which, according to my understanding, creates a strong reference cycle. Is my understanding correct? If so, how can we break the strong reference cycle — using a capture list, or is there any other way as well? Thanks
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118
Oct ’25