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:

1. How to get Ip address in swift
2. How do I get the IP address of a local hostname in local network in Swift
3. Swift - Get device's WIFI IP Address

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

Answer 1

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