Troubleshoot Mac IP Settings

Understanding Internet Addressing

When it comes to the Internet, you may be assigned a Public IPv4 address, such as 128.42.171.24, or an IPv6 address like 2000:8ddd:71ce:d838:17a1:5c3e:f5a8:9b8. You can verify this information by visiting https://test-ipv6.com/. However, it can be challenging for those who are not well-versed in technology to communicate these addresses or even identify MAC addresses like 21:a5:95:ae:4b:4f. This can lead to errors and can become complicated rather quickly, and it does not provide any historical data.

Navigating the World Wide Web

When attempting to access a webpage, such as https://mclaughlin.net, you start by contacting a DNS server to convert the host portion (mclaughlin) and the Top Level Domain (net) of the URL into an IP address, such as 58.250.4.42. Your computer and browser include their type with all web requests, for example:
Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)

The Significance of Default Gateway

The default gateway is typically an automatically configured address via DHCP. You receive a default gateway, such as 192.0.0.143 (though they usually end in .1 or .254 depending on the scope size), and this is where your computer routes all its traffic. For those who want to delve into IPv6, we have an in-depth guide on how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux using:

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  192.0.0.143    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   fe80:9aa:9ac7:8ed1:c860%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): {87.6.182.208, 46.46.23.14}
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 21:a5:95:ae:4b:4f
  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 eb:ba:50:52:b9:b6
}

Fixing Connectivity Issues on Apple Devices

When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.

Troubleshooting Tools for Apple macOS / OSX

Whether you’re running OSX/macOS version 10.13.6, 11.3.9, or 12.0.3, there are various troubleshooting tools available. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams engaged in remote work and Work From Anywhere (WFA).

Leveraging Built-in Scripts

A useful tool on OSX/macOS is sudo wdutil info, which generates a current dump of wireless settings to the command line interface and can be configured to produce specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.

sudo nohup /usr/bin/sysdiagnose -u & will run the tool in the background and write logs to /var/tmp/<blah>.tar.gz. To run it interactively, though there is minimal interaction, you can use sudo /usr/bin/sysdiagnose and it will prompt a privacy warning. When not run in the background, it should open Finder in the correct location or you can navigate to /var/tmp manually. Note that the file sizes are approximately 300MB.

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Table 1.0 - Video Help