Troubleshoot MacOS No-access
Understanding How Internet Addresses Function
When using the Internet, you are assigned a Public IPv4 address, such as 120.62.255.98, or an IPv6 address, like 2000:bb81:fdbe:b865:a25a:f779:9cc1:51de. These addresses can be verified at https://test-ipv6.com/. However, for those who are not technically inclined, conveying these addresses or even referencing MAC addresses like 3f:8b:5f:05:39:52 can be prone to error and become complex quickly. Moreover, this method does not provide any historical data, especially concerning past issues.
Navigating the World Wide Web
Accessing a website, such as https://gleason-hayes.co, first involves connecting to a DNS server to convert the host portion (gleason-hayes) combined with the Top Level Domain (co) of the URL into an IP address, such as 34.246.93.23. In fact, your computer and browser include their type in all web requests, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured via DHCP. A default gateway like 192.0.0.242 is assigned (although they usually end in .1 or .254, depending on the scope size) and serves as the focal point for all outbound traffic from your computer. For IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/, but you can verify this 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 192.0.0.242 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:d578:3869:c2d2:4b54%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): {141.100.154.33, 119.146.27.79}
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 3f:8b:5f:05:39:52
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 b5:40:26:9a:86:7a
}
Diagnosing and Resolving Connectivity Issues
When it comes to transmitting data to your router, you may encounter connectivity issues at the physical and data layer while using either a wired or wireless (Wi-Fi) medium.
Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS 10.11.5, 11.0.7, or 12.3.4, there is a variety of troubleshooting tools available. However, manual actions and scripts do not provide a continuous set of correlated values over time. This is where automated remote troubleshooting becomes beneficial, especially for teams that are adopting remote work and Work From Anywhere (WFA) policies.
Utilizing Pre-Existing Scripts
An effective tool for troubleshooting on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings through the CLI. It can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs (although many are only relevant to wireless settings, similar to wdutil).
To run it in the background and output logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive process, run sudo /usr/bin/sysdiagnose and navigate to the correct location in Finder or via /var/tmp (using Cmd+Shift+G in Finder). Keep in mind that the file size is approximately 300MB.
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