How To Troubleshoot Mac No-access
Explanation of Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address such as 39.61.200.13 or 2000:5146:ed56:a042:431a:2c5c:e317:a107. You can verify this by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not technologically inclined can be prone to errors and can become complex, especially when dealing with MAC addresses like ab:c1:7a:f2:d8:0a. Moreover, it does not provide any historical data, particularly from previous issues.
Navigating the World Wide Web
When you want to visit a website such as https://haag.net, your computer first contacts a DNS server to convert the host portion (haag) along with the Top Level Domain (net) of the URL to an IP address, for example, 136.201.236.59. During this process, your computer and browser include details about its type in all web requests, for example:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP, such as 172.24.106.98 (though they commonly end in .1 or .254 depending on the scope size). This is the point where your computer sends all its traffic to be routed further. For IPv6, you can refer to a detailed explanation in our post how-to-fix-ipv6-connectivity/; alternatively, you can check on Mac or Linux with the following command:
ip -6 route
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 172.24.106.98 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 fe80:8e06:34c5:3717:48be%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): {68.177.47.29, 193.70.133.113}
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 ab:c1:7a:f2:d8:0a
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 cd:dd:a8:17:4f:ce
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may rely on either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Steps for Apple macOS / OSX
No matter which version of OSX/macOS you’re using - whether it’s 10.15.8, 11.3.4, or 12.1.2 - there are a variety of tools available for troubleshooting. However, these manual actions and scripts fail to provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One particularly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the command line interface, and can be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only related to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can run sudo /usr/bin/sysdiagnose, which will prompt a 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 direct Finder to the path. Just be mindful of the file sizes, which are around 300MB or so.
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