Check MacOS IP Settings
Explanation of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 32.62.126.213, or an IPv6 address like 2000:6118:a2a1:628a:4dbc:dd2:6787:726b. You can verify this using the service provided at https://test-ipv6.com/. However, explaining and conveying these addresses, or even referring to MAC addresses like 09:de:07:64:d5:1c, can quickly become complicated, especially for those unfamiliar with the technical aspects. Moreover, it does not provide any historical data, particularly from past issues.
Navigating the Web
When visiting a website such as https://robel.org, the initial step involves accessing a DNS server to convert the host portion (robel) combined with the Top Level Domain (org) of the URL into an IP address, like 221.72.48.123. Your computer and browser include their type in all web requests as well, 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 automatically configured address via DHCP. You will receive a default gateway, such as 192.168.136.180 (usually ending in .1 or .254 depending on the scope size), to which your computer directs all its traffic for further routing. For IPv6, a comprehensive guide is available on how-to-fix-ipv6-connectivity/, and you can verify 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 192.168.136.180 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 fe80:3ae4:2aab:9cfb:1cd1%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): {162.22.21.187, 2.25.64.26}
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 09:de:07:64:d5:1c
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 d8:02:18:61:b6:1b
}
Solutions for Resolving Wired and Wireless Connectivity Issues
Whether you are utilizing a wired or wireless (Wi-Fi) medium to transmit data to your router, issues at the physical and data layer can arise.
Troubleshooting Tips for Apple macOS / OSX Users
Irrespective of the version of OSX/macOS you are running, such as 10.13.6, 11.5.1, or 12.1.1, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. Remote automated troubleshooting becomes crucial, especially for teams embracing remote work and Work From Anywhere (WFA).
Utilize In-Built Scripts for Assistance
An invaluable tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be utilized to generate comprehensive logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, use sudo /usr/bin/sysdiagnose, which opens Finder in the correct location or allows navigation to /var/tmp for file access. Be cautious of large file sizes, approximately 300MB.
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