It was mentioned in the keynote that there are changes/improvements in the switching between Wi-Fi and cellular. Where can I find more details about the expected changes?

Hello, We recently moved to the NWPath.Status implementation for reachability, is that the same reachability that powers URLSessionConfiguration.waitsForConnectivity? Or does the NWPath implementation rely on a specific network path such as cell only or wifi only? Is using NWPath still the best way to measure if the network is reachable? Thank you!

We have observed a per-process limitation on the number of simultaneous nw_connection_t objects in certain macOS environments. On some systems, this limit does not appear to apply, but on others the limitation is reproducible. When a process attempts to establish a large number of connections (e.g. 512+), some connections enter the nw_connection_state_waiting state and report the POSIX error “Cannot allocate memory”. These connections remain stuck indefinitely, even after other connections are deallocated and resources should theoretically be available again. This behavior severely impacts use cases such as transparent proxies implemented via the NetworkExtension framework, which intercept system-wide traffic and must open connections on behalf of all client processes. In this scenario, a per-process limit effectively becomes a system-wide limit, leading to unexpected and hard-to-diagnose network failures in client applications. Can we expect a relaxation of these restrictions for network extensions in the future? Could you please suggest some workarounds to bypass the restriction? By the way, now we have to fallback to BSD socket implementation of the outgoing connections, possibly braking the chain of TransparentProxies as the second proxy in the chain can’t get the originator of the intercepted flow (it sees the first proxy instead).

In iOS 27, there was mention of improved seamless WiFi/cell switching. Is my understanding correct that the phone is now more likely to switch to cellular when the signal from the WiFi access point is poor? Clarification on how this works would be appreciated.

Given the details are undocumented "feature" of VPN/networking (but shared by an engineer in a 1:1 lab at WWDC24) I'm not including details here. That said, it seems surprising that VPNs can suddenly disconnect overnight with no warning. Can this bug fix be prioritized during the iOS 27 cycle?

Thanks for being here! What is the behavior of this flag? The documentation is scant, to say the least.

When enforceRoutes = YES is set on a split tunnel VPN configuration containing only excluded routes, all traffic matching the included routes is silently dropped — no packets reach the VPN tunnel. Only the excluded routes route correctly via the physical adapter. Setting enforceRoutes = NO with an identical configuration restores full connectivity immediately, confirming the issue is specific to the combination of enforceRoutes = YES and a non-empty excludedRoutes. This has been verified on iPadOS 26. Test Environment Device: iPad pro 4th gen OS Version: iPadOS 26.0 VPN Type: NEPacketTunnelProvider VPN Configuration (NEPacketTunnelNetworkSettings) tunnelRemoteAddress = 103.135.123.108 DNSSettings = { protocol = cleartext server = (10.34.250.51) } IPv4Settings = { configMethod = manual addresses = (10.34.247.235) subnetMasks = (255.255.255.255) includedRoutes = ( { destinationAddress = 0.0.0.0 destinationSubnetMask = 0.0.0.0 } ) excludedRoutes = ( { destinationAddress = 10.168.10.182 destinationSubnetMask = 255.255.255.255 } ) overridePrimary = NO } MTU = 1400 enforceRoutes = YES includeAllNetworks = NO Reproduction Steps Configure NEPacketTunnelProvider with the settings above Set protocolConfiguration.enforceRoutes = YES Set protocolConfiguration.includeAllNetworks = NO Establish VPN connection and wait for Connected status Attempt to access any internet resource Observed Behavior Excluded route (10.168.10.182) correctly routes via physical adapter — confirmed in Wireshark Included routes (0.0.0.0/0) — zero packets visible in Wireshark on any interface, traffic completely dropped Internet fully inaccessible — no DNS responses, no TCP connections established Setting enforceRoutes = NO with an identical route configuration and all other settings unchanged restores full internet connectivity immediately. No other change is made.

We are investigating bridged Wi-Fi DHCP behavior on recent macOS releases and would appreciate some clarification regarding the net.link.bridge.use_dhcp_xid sysctl. We observed that with the default setting, DHCP packets transmitted from a virtual machine through a bridged Wi-Fi interface may have their DHCP client identity modified (chaddr). In our testing, setting: net.link.bridge.use_dhcp_xid=0 prevents this behavior and restores the DHCP packet format observed on older macOS versions. We would like to better understand the intended purpose of this sysctl: What functionality does net.link.bridge.use_dhcp_xid control internally? Besides DHCP chaddr rewriting, what other bridge or DHCP processing behavior is affected by this setting? Is this sysctl related to DHCP snooping, anti-spoofing protection, Wi-Fi bridging compatibility, or another mechanism? Is the current default behavior (use_dhcp_xid=1) a recent change introduced in macOS 26.4.x? Is the modified DHCP behavior considered expected and supported, or is it intended as an implementation detail? For additional context, we previously submitted feedback regarding DHCP handling for virtual machines using Virtualization Framework. Since packet modification is restricted from user space, we are wondering whether this sysctl is related to DHCP processing implemented by the bridge subsystem to address DHCP spoofing, client identification, or Wi-Fi bridging limitations. One concern we have is that net.link.bridge.use_dhcp_xid appears to be a system-wide setting. In our use case, DHCP handling requirements may differ between virtual machines, networks, and environments. As a result, changing a global bridge behavior for the entire host system is not always desirable. If this sysctl is intended to control DHCP processing for bridged virtual machines, would it be possible to expose similar functionality on a per-interface, per-bridge, or per-VM basis rather than as a host-wide setting? This would allow virtualization products to adapt DHCP behavior to specific network environments without affecting all bridged networking on the host. One additional question: Apple suggested making this setting persistent via /etc/sysctl.conf. However, this file does not exist by default on our macOS 26.4.x systems. Is /etc/sysctl.conf still a supported mechanism for persistent sysctl configuration, or is there a preferred modern alternative? Any documentation or implementation details that can be shared would be greatly appreciated.

Hello, Our app makes a lot of requests and we are starting to wrangle them into a priority queue style structure for ordered execution. As we get further into that work, is there guidance on how many requests URLSession will queue and does that change based on connectivity or network quality? Thank you!

Moin! Can you comment if anything of the happy eyeballs version 3 IETF draft ( https://datatracker.ietf.org/doc/draft-ietf-happy-happyeyeballs-v3/ ) is in the 27 version of OSes? So long -Ralf

A performance bottleneck we often hit is that we seem to be constrained by issuing a single sys call per packet. On platforms where vectored IO is supported, we can unlock 5x performance gains. Whilst we can read arrays of packets via the network extension API, the memory and concurrency model of that API seems to not be well documented, and I am not aware of any way to do vectored I/O on a UDP socket. Will we see an FFI friendly API for vectorised networking anytime soon? As an addendum - we are aware of sendmsg_x and recvmsg_x but we dare not ship an iOS app using those functions directly.

Recently, the number of cybersecurity attacks has been steadily increasing. For corporate users, access is provided through special extensions that allow traffic from a specific application to be routed through a tunnel. However, connecting a device to an MDM solution is convenient for large customers, but it creates challenges for small companies and developer teams that need to secure their network connections (for example, when a specific application must be isolated so that all of its traffic is routed exclusively through the tunnel), or protect their local infrastructure by preventing external applications from establishing network connections to unexpected servers (for instance, some applications may make requests to random servers in an attempt to determine their network environment).

I'd imagine that RCS messaging is part of the package of excluded services when excludeCellularServices is set to true. Is that accurate? Documentation

When my URLSessionDelegate receives a server trust challenge (NSURLAuthenticationMethodServerTrust) and I respond with .useCredential for an enterprise self-signed cert, does the decision get cached for subsequent requests on the same URLSession, or is the delegate called again on every connection to the same host?

Hello, I filed feedback 22592307 around crashes my team and I are seeing in libquic now that we have adopted HTTP/3 for a large portion of our network usage. During the state of the union it was stated that libquic has been fully re-written in Swift by the WebKit team. Is that swift version the new implementation of libquic in iOS 27? If not, what will be the best way to adopt it without leaving the URLSession ecosystem?

Is the system default for this still false as of the OS 27 releases? When would you recommend setting it to true?

With iOS 27's improvements to seamless Wi-Fi/cellular transitions, is there guidance for apps and frameworks doing background network requests on how to handle a transition mid-request? Do in-flight URLSession tasks survive a network path change automatically, or should apps build their own retry logic?

I have an iOS app that now cannot connet to websocket servers when building with new SDKs. The app that i have deployed in appstore can connect to the existing websocket servers we use but when i build the same code with the new SDKs (Nex XCode) the app connects to the websocket server and then disconnect right after that so no messages are received and no messages are sent. What has changed and what do i need to change in the app? Or do i need to change somehing else somewhere else?

We are seeing a consistent crash on iOS 26 that does not reproduce on iOS 17 or iOS 18. The crash occurs on a background thread ("com.apple.network.connections") with no application code in the crashed thread's stack. The crash trace begins in quic_migration_probe_path and terminates in nw_protocol_data_access_buffer + 180, suggesting a use-after-free or buffer lifetime violation during QUIC connection path migration (e.g., Wi-Fi ↔ Cellular handoff). This crash does not appear to be reproducible on demand — it correlates with network path transitions while QUIC connections are active. Our app uses standard URLSession with default/ephemeral session configurations and does not explicitly enable HTTP/3; iOS 26 is automatically upgrading eligible connections. Crash thread (abbreviated): 0 libquic.dylib quic_conn_send_packet + 144 1 libquic.dylib quic_conn_continue_sending + 424 2 libquic.dylib __quic_conn_send_frames_for_key_state_block_invoke_2 + 1244 3 Network nw_protocol_data_access_buffer + 180 ← crash 4 Network nw_protocol_data_copy_buffer 5 Network nw_endpoint_flow_output_frames 6 libquic.dylib quic_conn_send_frames_for_key_state 7 libquic.dylib quic_conn_send_frames 8 libquic.dylib quic_migration_probe_path + 1464 9 libquic.dylib quic_migration_path_established + 2608 10 libquic.dylib __quic_migration_path_event_block_invoke.21 11 libquic.dylib quic_migration_path_event 12 Network nw_protocol_implementation_connected There is no app code in the crashed thread. This is a regression introduced in iOS 26, where libquic.dylib was separated into its own dynamic library and new path migration probe logic was introduced. iOS → iOS 26 Networking → URLSession / Network.framework

When a VPN is active, RCS messaging does not work on iOS 18. I work on an iOS VPN app, and we were very appreciative of the excludeCellularServices network flag that was released during the iOS 16 cycle. It's a great solution to ensure the VPN doesn't interfere with cellular network features from the cellular provider. Separately - As a user, I'm excited that iOS 18 includes RCS messaging. Unfortunately, RCS messaging is not working when our VPN is active (when checking on the iOS 18 release candidate). My guess is that RCS is not excluded from the VPN tunnel, even when excludeCellularServices is true. It seems like RCS should be added in this situation, as it is a cell provider service. Can RCS be added as a service that is excluded from the VPN tunnel when excludeCellularServices is true? (I've also sent this via feedback assistant, as 15094270.)