DiagnOSe Mac No-access
Understanding Internet Addressing
When using the Internet, you are assigned a unique public IPv4 address such as 158.242.4.87 or an IPv6 address like 2000:ab34:3124:891c:addc:e837:480d:5afa. You can verify this information using https://test-ipv6.com/. However, conveying these addresses, or even MAC addresses like da:2f:57:30:e9:3e, to those who are not well-versed in technology can be prone to errors and become complex. Moreover, this method does not provide any historical data, particularly when past issues arise.
Navigating the World Wide Web
When trying to visit a website such as https://schmidt.name, you begin by accessing a DNS server to convert the host portion (schmidt) along with the Top Level Domain (name) of the URL into an IP address like 188.212.28.112. Your computer and browser also send their type along with all web requests, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. You are assigned a default gateway, such as 10.213.148.177 (although they usually end in .1 or .254, depending on the scope size), and this is where your computer directs all of its traffic to be routed further. For IPv6 troubleshooting, we provide an in-depth exploration in our article 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 10.213.148.177 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 fe80:2b4:629e:bc09:faa8%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): {217.246.252.58, 159.139.219.210}
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 da:2f:57:30:e9:3e
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 0a:a7:93:e6:4b:7a
}
Resolving Issues with Wired and Wireless Connections
When sending data to your router, you may utilize either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX or macOS you are using, whether it’s 10.15.9, 11.6.2, or 12.0.2, there are various tools available for troubleshooting. 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 are engaged in remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting purposes. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although it primarily provides point-in-time information related to wireless, 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 &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, although it will display 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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