How Do You Troubleshoot Mac No-access
Understanding Internet Addressing
When using the Internet, you will be assigned a public IP address such as 149.41.91.73 for IPv4 or 2000:49b5:9299:e95f:2264:7949:a2e8:1ef2 for IPv6. You can verify your IP address at https://test-ipv6.com/. However, communicating these addresses, or even MAC addresses like da:31:4c:27:ad:54, can be challenging for those who are not technically inclined. Moreover, this method does not provide historical data, particularly when dealing with past issues.
Navigating the World Wide Web
When accessing a website such as https://lakin.co, your device initially contacts a DNS server to convert the host portion (lakin) in combination with the Top Level Domain (co) of the URL to an IP address like 182.217.34.11. Additionally, your computer and browser include specific information in all web requests, for example: 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 address that is automatically configured via DHCP. This default gateway, such as 10.181.201.126 (usually ending in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed onwards. For IPv6, you can find detailed instructions on how-to-fix-ipv6-connectivity/, or check on Mac or Linux using the following command:
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 10.181.201.126 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:b7fb:d49d:4fef:2b98%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): {95.81.131.136, 140.230.224.103}
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:31:4c:27:ad:54
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 51:59:0c:7d:53:b8
}
Fixing Connection Issues for Wired and Wireless Networks
When it comes to sending data to your router, you have the option of using 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/macOS you are using, whether it’s 10.14.7, 11.0.2, or 12.3.7, there are various tools available for troubleshooting. However, these tools and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that accommodate remote work and Work From Anywhere (WFA).
Integrated Scripts That Offer Assistance
On OSX/macOS, the sudo wdutil info tool is quite useful as it provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool is more comprehensive and can generate a wide range of logs, although many of these are point-in-time records related to wireless, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. You can also run it interactively with the command sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes, around 300MB more or less.
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