How To Understand Mac No-access
Demystifying Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 address like 36.142.2.17 or an IPv6 address like 2000:566e:6680:b044:8f9a:f992:e9cc:51e4. The verification of these addresses can be done through https://test-ipv6.com/. However, for those who are not technically inclined, relaying these addresses or even the MAC addresses like 35:92:6f:c6:d4:a0 can be prone to errors and can become complicated in a short span of time. Moreover, this method does not provide any historical data, particularly when past issues need to be referred to.
Navigating the World Wide Web
When attempting to reach a website, such as https://stokes-kunde.net, you first connect to a DNS server to convert the host portion (stokes-kunde) in combination with the Top Level Domain (net) of the URL into an IP address like 130.81.63.58. Every time your computer and browser sends a web request, it includes its type, for example, Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
Ordinarily, your default gateway is an automatically configured address through DHCP. A default gateway such as 172.21.56.48 (although they typically end in .1 or .254, depending on the scope size) is where your computer directs all its traffic to be routed further. For IPv6, a detailed guide can be found at how-to-fix-ipv6-connectivity/, or you can 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 172.21.56.48 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 fe80:3962:9564:a7f1:b0aa%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): {57.89.252.244, 106.182.245.151}
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 35:92:6f:c6:d4:a0
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 74:d8:e2:6c:0b:45
}
Addressing Connectivity Issues in Wired and Wireless Networks
When it comes to data transmission, you may opt for either a wired or wireless (Wi-Fi) medium to connect to your router at the physical and data layer.
Tips and Tricks for Resolving Network Problems on Apple macOS
No matter which version of OSX or macOS you are currently using, whether it’s 10.11.6, 11.6.5, or 12.1.5, there are various troubleshooting tools at your disposal. However, these manual methods and scripts often fail to provide a comprehensive set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that adopt remote work and the Work From Anywhere (WFA) approach.
Leveraging the Power of Built-in Scripts
One of the most useful tools for OSX/macOS users is the sudo wdutil info command, which provides a detailed report of current wireless settings via the CLI. Additionally, the sysdiagnose tool offers a more comprehensive solution by generating a wide range of logs, although many of these logs are only relevant to the wireless aspect, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the following command: sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose. Just keep in mind that running it interactively will trigger a privacy warning. The logs are stored in /var/tmp, and you can navigate there via Finder or by using the Cmd+Shift+G shortcut in Finder to locate the path. However, be cautious of the file sizes, which can be around 300MB or more.
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