How to get the IP Address of Router in Swift iOS

Question

I want to get the IP address of the connected router from my iPhone. I'm getting the IP address of my iPhone only.

Is there any way by which I can get the host/router IP address?

BTW I already reviewed following links but no solutions there:

I'm trying to do it in Swift 5 with XCode 12.4

@Anbu.Karthik, can you please explain which external API I should call? Do I need to create them separately? — SandeepM, May 27 '21 at 04:51
You should check https://stackoverflow.com/questions/58503680/is-there-any-way-to-get-the-default-gateway-ip-on-ios-using-swift — the_exclusive, May 27 '21 at 08:58

iUrii · Answer 1 · 2021-06-01T06:14:55.110

You can get IP address of your default gateway from the routing table using sysctl but first you should define needed structures and constants because Darwin.net.route or <route.h> is not exposed to iOS SDK:

let RTAX_GATEWAY = 1
let RTAX_MAX = 8

public struct rt_metrics {
    public var rmx_locks: UInt32 /* Kernel leaves these values alone */
    public var rmx_mtu: UInt32 /* MTU for this path */
    public var rmx_hopcount: UInt32 /* max hops expected */
    public var rmx_expire: Int32 /* lifetime for route, e.g. redirect */
    public var rmx_recvpipe: UInt32 /* inbound delay-bandwidth product */
    public var rmx_sendpipe: UInt32 /* outbound delay-bandwidth product */
    public var rmx_ssthresh: UInt32 /* outbound gateway buffer limit */
    public var rmx_rtt: UInt32 /* estimated round trip time */
    public var rmx_rttvar: UInt32 /* estimated rtt variance */
    public var rmx_pksent: UInt32 /* packets sent using this route */
    public var rmx_state: UInt32 /* route state */
    public var rmx_filler: (UInt32, UInt32, UInt32) /* will be used for TCP's peer-MSS cache */
}

public struct rt_msghdr2 {
    public var rtm_msglen: u_short /* to skip over non-understood messages */
    public var rtm_version: u_char /* future binary compatibility */
    public var rtm_type: u_char /* message type */
    public var rtm_index: u_short /* index for associated ifp */
    public var rtm_flags: Int32 /* flags, incl. kern & message, e.g. DONE */
    public var rtm_addrs: Int32 /* bitmask identifying sockaddrs in msg */
    public var rtm_refcnt: Int32 /* reference count */
    public var rtm_parentflags: Int32 /* flags of the parent route */
    public var rtm_reserved: Int32 /* reserved field set to 0 */
    public var rtm_use: Int32 /* from rtentry */
    public var rtm_inits: UInt32 /* which metrics we are initializing */
    public var rtm_rmx: rt_metrics /* metrics themselves */
}

public func getDefaultGateway() -> String? {
    var name: [Int32] = [
        CTL_NET,
        PF_ROUTE,
        0,
        0,
        NET_RT_DUMP2,
        0
    ]
    let nameSize = u_int(name.count)
    
    var bufferSize = 0
    sysctl(&name, nameSize, nil, &bufferSize, nil, 0)
    
    let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
    defer { buffer.deallocate() }
    buffer.initialize(repeating: 0, count: bufferSize)
    
    guard sysctl(&name, nameSize, buffer, &bufferSize, nil, 0) == 0 else { return nil }
    
    // Routes
    var rt = buffer
    let end = rt.advanced(by: bufferSize)
    while rt < end {
        let msg = rt.withMemoryRebound(to: rt_msghdr2.self, capacity: 1) { $0.pointee }
        
        // Addresses
        var addr = rt.advanced(by: MemoryLayout<rt_msghdr2>.stride)
        for i in 0..<RTAX_MAX {
            if (msg.rtm_addrs & (1 << i)) != 0 && i == RTAX_GATEWAY {
                let si = addr.withMemoryRebound(to: sockaddr_in.self, capacity: 1) { $0.pointee }
                if si.sin_addr.s_addr == INADDR_ANY {
                    return "default"
                }
                else {
                    return String(cString: inet_ntoa(si.sin_addr), encoding: .ascii)
                }
            }
            
            let sa = addr.withMemoryRebound(to: sockaddr.self, capacity: 1) { $0.pointee }
            addr = addr.advanced(by: Int(sa.sa_len))
        }
        
        rt = rt.advanced(by: Int(msg.rtm_msglen))
    }
    
    return nil
}

// How to use
if let ip = getDefaultGateway() {
    print(ip)
}
// Prints: 192.168.1.1

Can we get IP address of the connected Access Point in iOS if the gateway is 0.0.0.0? — Akshada-Systematix, Jun 02 '21 at 11:16
We tried this code and we are getting gateway IP address of connected Access Point and in my case that is 0.0.0.0. But we want IP address of connected Access Point rather than its gateway IP. Can you please help? — Akshada-Systematix, Jun 04 '21 at 16:39
@Akshada-Systematix My example show how you can access to your routing table and get info about a default gateway. The routing table has all know routes such as host, subnet and default and you can get a needed route from the list by analyzing its flags. FreeBSD Gateways and Routes - https://docs.freebsd.org/en/books/handbook/advanced-networking/#network-routing — iUrii, Jun 07 '21 at 18:49

How to get the IP Address of Router in Swift iOS

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