How Can I DiagnOSe Mac IP Settings

Understanding Operation of Internet Addressing When using the Internet, individuals may be assigned a Public IPv4 address such as 98.255.209.64 or an IPv6 address like 2000:4a5c:b3f:bb4d:784c:d1b2:b34a:b53e. Verification of these addresses can be done at https://test-ipv6.com/. However, expressing these addresses or MAC addresses like d5:a8:87:3c:97:8a can be challenging, especially for those without technical expertise. Understanding Operation of Internet Addressing When using the Internet, individuals may be assigned a Public IPv4 address such as 98.255.209.64 or an IPv6 address like 2000:4a5c:b3f:bb4d:784c:d1b2:b34a:b53e. Verification of these addresses can be done at https://test-ipv6.com/. However, expressing these addresses or MAC addresses like d5:a8:87:3c:97:8a can be challenging, especially for those without technical expertise.

Understanding Operation of Internet Addressing

When using the Internet, individuals may be assigned a Public IPv4 address such as 98.255.209.64 or an IPv6 address like 2000:4a5c:b3f:bb4d:784c:d1b2:b34a:b53e. Verification of these addresses can be done at https://test-ipv6.com/. However, expressing these addresses or MAC addresses like d5:a8:87:3c:97:8a can be challenging, especially for those without technical expertise. Furthermore, this method does not provide historical data, particularly for past issues.

Accessing a web page, such as https://hackett.io, initially involves a query to a DNS server. The server translates the host portion (hackett) in combination with the Top Level Domain (io) of the URL into an IP address, such as 214.125.239.118. In all web requests, your computer and browser transmit their type, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko

Significance of Default Gateways

The default gateway is typically an auto-configured address provided via DHCP. The default gateway, such as 192.0.0.156 (usually ending in .1 or .254 depending upon the scope size), is the point to which your computer forwards all its traffic for routing. For IPv6, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/. Users can also check on Mac or Linux using the following command:

IPv4 Routes and the Host IPv4 Route Table (inc. VPN)

netstat -rn -f inet | egrep -i "default|0/1|128.0/1"

0/1      172.18.12.193  UGScg  utun3
default  192.0.0.156    UGScg  en0
128.0/1  172.18.12.193  UGSc   utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v4 address space.

IPv6 Routes and the Host IPv6 Route Table (inc. VPN)

netstat -rn -f inet6 | egrep -i "default|2000::/3"

If you have IPv6 active the above should return at least one route (as per below) via a known interface such as “en0 " on a Mac.

default   fe80:6eff:4249:cb45:2d86%en0  UGcg   en0
default   fe80::%utun0                   UGcIg  utun0
default   fe80::%utun1                   UGcIg  utun1
default   fe80::%utun2                   UGcIg  utun2
2000::/3  utun3                          USc    utun3

Note: We are not just looking for the default but also for any VPN that overrides the public v6 address space.

Debugging DHCP for both IPv4 and IPv6

To get a look at the low level DHCP configuration (Mac/Linux):

ipconfig getpacket en0

...
domain_name_server (ip_mult): {18.156.85.55, 226.48.233.186}
end (none):
...

So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but…

ipconfig getv6packet en0

DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
  CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr d5:a8:87:3c:97:8a
  DNS_SERVERS (23) Length 32: 2606:4700:4700::1111, 2001:4860:4860::8844
  DOMAIN_LIST (24) Length 0:  Invalid
  SERVERID (2) Length 10: DUID LL HW 1 Addr 7d:fa:69:77:fe:43
}

Solutions for Addressing Connectivity Issues

When it comes to transferring data to your router, you may encounter connectivity issues at the physical and data layer whether you are using a wired or wireless (Wi-Fi) medium.

Troubleshooting Techniques for Apple macOS / OSX Users

Regardless of the version of OSX/macOS you are utilizing - be it 10.12.2, 11.5.7, or 12.2.5, there is a wide array of tools available for addressing connectivity issues. However, these manual actions and scripts do not offer a set of interconnected values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA) policies.

Utilizing Built-in Scripts for Assistance

An invaluable tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool offers a more comprehensive range of logs (albeit many are point-in-time with regards to wireless, similar to wdutil).

To run sysdiagnose in the background and generate logs at /var/tmp/<blah>.tar.gz, the command sudo nohup /usr/bin/sysdiagnose -u & can be used. Alternatively, for an interactive (albeit minimal interaction) experience, you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, allowing you to navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. It’s worth noting that the file sizes are approximately 300MB.

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