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Some links on getting MacOS network interfaces and DHCP information

Posted by jpluimers on 2021/07/30

One day I’ll put this in a script that shows all DHCP information for all network interfaces.

For now some links I will need when writing that script.

Many of the below commands are also in [WayBack] Command-Line Tools: The Missing Manpages (Mac OS X for Unix Geeks).

Shows all interfaces:

networksetup -listallhardwareports

Show any DHCP server on any interface (but does not list interfaces):

system_profiler SPNetworkDataType | grep "Server Identifier"

  • [WayBack] Find the IP address of your DHCP server. – Apple Community

    Other options would be:

    system_profiler SPNetworkDataType | grep "Server Identifier"

  • [WayBack] Crabeater: Stateful Parser in Python

    I came up with a method for parsing the output of system commands that require knowledge of previous lines to provide context. An example of this is parsing the MAC addresses for interfaces on a Mac running OS X Leopard using the system_profiler command. The output of the command has various levels of sections. The first level of section headers aren’t indented at all. The next level is indented four spaces and the next six spaces.

    For this task I want to parse out the interface names, which are indented four spaces, but there are plenty of similar subsection headers that are not interfaces. The context I need is whether or not the current line is in the Network section.

    I came up with a way to implement this where the Parser is a class and has an instance variable named “state” that holds the correct method to use to parse the next line.

    Notice that h2Pattern matches any subsection header, but I only use it to match a line if the line is inside the Network section (i.e. it is only used inside the network method.)

 

For a NIC en0, shows the most recent DHCP packet information:

ipconfig getpacket en0 
  • [WayBack] Find and display a DHCP server’s IP address – Mac OS X Hints

    According to the manual page for ipconfig, this command appears to be unique to Mac OS X, first introduced in the Public Beta! The command will display a bunch of useful info, including:

    • server_identifier (ip): That’s your DHCP server’s IP address.
    • yiaddr: Your machine’s IP address.
    • chaddr: Your machine’s MAC address.
    • domain_name_server: Your domain name server(s).

    There’s much more in the output. Keep in mind that if you have entered an IP address manually, then you’ll get no output from this command.

  • [WayBack] Find the IP address of your DHCP server. – Apple Community

    Other options would be:

    system_profiler SPNetworkDataType | grep "Server Identifier"

    and to narrow down the one you used:

    ipconfig getpacket en0 | grep siaddr

    ipconfig getpacket en1 | grep siaddr

    There may be some mileage in using ifconfig as well? If you’re connected over Wi-Fi holding down the option key whilst clicking on the Airport Icon in the Menu Bar will also show you the WAP’s IP address, which in some cases will also be the DHCP server.

  • [WayBack] Viewing DHCP information on an OS X system
    $ ipconfig getoption en0 server_identifier
    192.168.2.1
    $ ipconfig getoption en0 router
    192.168.2.1
    $ ipconfig getoption en0 subnet_mask
    255.255.255.0
    $ ipconfig getoption en0 domain_name_server
    192.168.2.1
    $ ipconfig getoption en0 lease_time
    86400
    $ ipconfig getoption en0 domain_name
    $

    $ ipconfig getpacket en0
    op = BOOTREPLY
    htype = 1
    flags = 0
    hlen = 6
    hops = 0
    xid = 0xceb36b13
    secs = 0
    ciaddr = 0.0.0.0
    yiaddr = 192.168.2.51
    siaddr = 0.0.0.0
    giaddr = 0.0.0.0
    chaddr = ac:bc:32:ce:d3:f5
    sname = 
    file = 
    options:
    Options count is 7
    dhcp_message_type (uint8): ACK 0x5
    server_identifier (ip): 192.168.2.1
    lease_time (uint32): 0x15180
    subnet_mask (ip): 255.255.255.0
    router (ip_mult): {192.168.2.1}
    domain_name_server (ip_mult): {192.168.2.1}
    end (none): 
    $
  • [WayBack] ipconfig Man Page – macOS – SS64.com
    COMMANDS
    
         The ipconfig utility provides several commands:
    
         waitall     Blocks until all network services have completed configuring,
                     or have timed out in the process of configuring.  This is
                     only useful for initial system start-up time synchronization
                     for legacy network services that are incapable of dealing
                     with dynamic network configuration changes.
    
         getifaddr interface-name
                     Prints to standard output the IP address for the first net-
                     work service associated with the given interface.  The output
                     will be empty if no service is currently configured or active
                     on the interface.
    
         ifcount     Prints the number of interfaces that IPConfiguration is capa-
                     ble of configuring.  The value that's printed will not change
                     unless relevant network interfaces are either added to or
                     removed from the system.
    
         getoption interface-name (option-name | option-code)
                     Prints the BOOTP/DHCP option with the given name or option
                     code integer value.  See bootpd(8) for option code names.  If
                     an option has multiple values e.g. domain_name_server, only
                     the first value is printed.
    
         getpacket interface-name
                     Prints to standard output the DHCP/BOOTP packet that the
                     client accepted from the DHCP/BOOTP server.  This command is
                     useful to check what the server provided, and whether the
                     values are sensible.  This command outputs nothing if
                     DHCP/BOOTP is not active on the interface, or the attempt to
                     acquire an IP address was unsuccessful.
    
         getv6packet interface-name
                     Prints to standard output the latest DHCPv6 packet that the
                     client accepted from the DHCPv6 server.  In the case of
                     stateful DHCPv6, it corresponds to the last packet from the
                     server that contained addressing information.  This command
                     is useful to check what the server provided, and whether the
                     values are sensible.  This command outputs nothing if DHCPv6
                     is not active on the interface.
    
         set interface-name NONE
         set interface-name (DHCP | BOOTP)
         set interface-name (MANUAL | INFORM) ip-address subnet-mask
         set interface-name NONE-V6
         set interface-name AUTOMATIC-V6
         set interface-name MANUAL-V6 ipv6-address prefix-length
         set interface-name 6TO4
                     Sets the interface to have a new temporary network service of
                     the given type.  Any existing services on the interface for
                     the particular protocol (IPv4 or IPv6) are first de-config-
                     ured before the new service is instantiated.
    
                     If NONE is specified, all existing IPv4 services are de-con-
                     figured.  If NONE-V6 is specified, all existing IPv6 services
                     are de-configured.
    
                     DHCP and BOOTP require no additional arguments. The IP
                     address, subnet mask, router, and DNS information are
                     retrieved automatically.
    
                     Both MANUAL and INFORM require the specification of an IP
                     address ip-address and a subnet mask subnet-mask.
    
                     The INFORM service configures the IP address statically like
                     MANUAL, but then broadcasts DHCP INFORM packets to retrieve
                     DHCP option information. If the DHCP server responds and sup-
                     plies a subnet mask, that subnet mask is used instead of the
                     specified subnet-mask.
    
                     AUTOMATIC-V6 requires no additional arguments.  The IPv6
                     address, prefix length and router are retrieved automati-
                     cally.
    
                     MANUAL-V6 requires the specification of the IPv6 address
                     ipv6-address and a prefix length prefix-length.
    
                     6TO4 only works on Six To Four (IFT_STF) interfaces e.g.
                     stf0.  If it is specified on a non-IFT_STF interface, it has
                     the same effect as specifying NONE-V6.
    
                     The set command requires root privileges.
    
                     Note: The set command is very useful for debugging, but it
                     can't be used to configure a persistent service.  The tempo-
                     rary services that are created only remain until the next
                     network configuration change occurs. See scselect(8).
    
         setverbose level
                     Sets verbose mode logging in the IPConfiguration agent. Spec-
                     ify a level value of 0 to disable verbose logging, the
                     default.  Specify a value of 1 to enable verbose logging.
    
                     When enabled, useful debugging information is logged using
                     syslog(3) with level LOG_NOTICE.  In addition, the packet
                     trace file /var/log/com.apple.IPConfiguration.bootp is opened
                     and BOOTP/DHCP packets that are sent and received are printed
                     to the file.
    
                     The setverbose command requires root privileges.

    Examples

    Display your routers ip address:
    $ ipconfig getoption en0 router
    192.168.0.1

    Renew DHCP Lease
    $ sudo ipconfig set en0 DHCP

    Display all DHCP configuration details:

    $ ipconfig getpacket en0
         op = BOOTREPLY
         htype = 1
         dp_flags = 0
         hlen = 6
         hops = 0
         xid = 1956115059
         secs = 0
         ciaddr = 0.0.0.0
         yiaddr = 192.168.4.10
         siaddr = 192.168.4.1
         giaddr = 0.0.0.0
         chaddr = 0:3:93:7a:d7:5c
         sname = dhcp.mycompany.net
         file =
         options:
         Options count is 10
         dhcp_message_type (uint8): ACK 0x5
         server_identifier (ip): 192.168.4.1
         lease_time (uint32): 0x164a
         subnet_mask (ip): 255.255.255.0
         router (ip_mult): {192.168.0.1}
         domain_name_server (ip_mult): {8.8.4.4}
         domain_name (string): mycompany.net
         end (none):
    
    Display the DNS Server:
    $ ipconfig getoption en0 domain_name_server
        8.8.4.4
    
    Clear DNS Cache:
    $ sudo killall -HUP mDNSResponder

–jeroen

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