How Can I DiagnOSe MacOS IP Settings

Understanding Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 101.154.229.13, or an IPv6 address, such as 2000:b37b:beed:aaf5:b6e9:bf18:b92b:4c27. You can verify this information by visiting https://test-ipv6.com/. However, translating and communicating these addresses, as well as MAC addresses like a6:6d:ba:7a:77:8f, can be error-prone and complex, especially for those not well-versed in the technical aspects. Understanding Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 101.154.229.13, or an IPv6 address, such as 2000:b37b:beed:aaf5:b6e9:bf18:b92b:4c27. You can verify this information by visiting https://test-ipv6.com/. However, translating and communicating these addresses, as well as MAC addresses like a6:6d:ba:7a:77:8f, can be error-prone and complex, especially for those not well-versed in the technical aspects.

Understanding Internet Addressing

When using the Internet, you are assigned a Public IPv4 address, such as 101.154.229.13, or an IPv6 address, such as 2000:b37b:beed:aaf5:b6e9:bf18:b92b:4c27. You can verify this information by visiting https://test-ipv6.com/. However, translating and communicating these addresses, as well as MAC addresses like a6:6d:ba:7a:77:8f, can be error-prone and complex, especially for those not well-versed in the technical aspects. In addition, this method does not provide any historical data, especially for past issues.

When accessing a website, such as https://schumm.name, your computer first contacts a DNS server to convert the host name (schumm) and the Top Level Domain (name) of the URL into an IP address, such as 106.80.32.191. Your computer and browser also transmit their information with all web requests, such as
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285.

The Significance of Default Gateways

The default gateway is typically an automatically assigned address through DHCP. It usually takes the form of an address like 192.168.147.92 (though it generally ends in .1 or .254 depending on the scope size). This is where your computer forwards all its traffic to be routed further. For IPv6, you can find more detailed instructions on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux with:

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  192.168.147.92    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   fe80:83ee:3d22:11df:c2fa%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): {92.182.185.195, 210.117.130.80}
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 a6:6d:ba:7a:77:8f
  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 64:08:f4:73:a5:71
}

Troubleshooting Connectivity Issues for Wired and Wireless Networks

In order to transmit data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.

Solutions for Apple macOS / OSX Users

Regardless of whether you are using version 10.13.9, 11.5.2, or 12.0.4 of OSX/macOS, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that have adopted remote work and the Work From Anywhere (WFA) approach.

Utilizing Built-in Scripts for Assistance

A highly useful tool for OSX/macOS users is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can also generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is limited to point-in-time information related to wireless, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. For an interactive (though limited interaction) experience, you can run sudo /usr/bin/sysdiagnose, which 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 using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.

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