How To DiagnOSe Mac Connectivity
How the Functionality of Internet Addressing Is Established
When using the Internet, individuals might come across a Public IPv4 address such as 65.35.119.247 or an IPv6 address like 2000:28ca:fcd4:85b0:410c:65b:3a36:fa62. This information can be verified at https://test-ipv6.com/. However, conveying these addresses, or even citing MAC addresses like d8:99:11:34:ec:e1, can be prone to mistakes and become complicated. Moreover, it fails to provide historical data, particularly regarding past issues.
Navigating through the Internet
When attempting to visit a web page such as https://smith-lang.name, the initial step involves accessing a DNS server to convert the host section (smith-lang) along with the Top Level Domain (name) of the URL into an IP address like 211.72.135.6. Every web request from your computer and browser contains its type, for instance: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
Typically obtained through automatic configuration via DHCP, your default gateway is an address such as 192.0.0.177 (usually ending in .1 or .254 based on scope size), where your computer forwards all its traffic to be routed. For IPv6, detailed guidance can be found in how-to-fix-ipv6-connectivity/, and it can be verified on Mac or Linux with the following commands:
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 192.0.0.177 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:c082:744a:103:eaaf%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): {47.78.46.36, 210.93.43.132}
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 d8:99:11:34:ec:e1
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 dd:26:cd:20:4e:c3
}
How to Solve Issues with Wired and Wireless Connections
When it comes to getting your data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of which version of OSX/macOS you are using, whether it’s 10.14.7, 11.2.7, or 12.3.8, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool for OSX/macOS users is the sudo wdutil info command, which provides a dump to the CLI of current wireless related settings and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although much of it is only relevant to wireless issues such as wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, use the sudo nohup /usr/bin/sysdiagnose -u & command. For an interactive experience, run sudo /usr/bin/sysdiagnose and take note of the privacy warning. When not run in the background, it should open Finder in the correct location or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. But be aware of the large file sizes, around 300MB more or less.
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