How To Troubleshoot Apple No-access
Understanding Internet Addressing
When using the internet, you will be assigned a public IP address, which can be in the form of IPv4 like 6.49.102.203 or IPv6 like 2000:6c4b:bab6:cbba:11f3:6bc5:8347:7efc. Verification of this information can be done through https://test-ipv6.com/. However, for those who are not technically inclined, communicating these addresses, or even referencing MAC addresses like 0d:1b:4d:f4:e6:aa, can quickly become complicated and error-prone. Moreover, it might not provide historical data, particularly from past incidents.
Navigating the World Wide Web
Accessing a web page such as https://renner.info involves an initial visit to a DNS server, which translates the host portion (renner) along with the Top Level Domain (info) of the URL into an IP address like 149.50.224.62. Interestingly, your computer and browser send their type with all web requests, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway is typically an automatically configured address through DHCP. A default gateway like 192.0.0.249 (although they often end in .1 or .254 based on the scope size) is where your computer directs all its traffic to be routed onwards. For IPv6, further information can be found in our in-depth guide on how-to-fix-ipv6-connectivity/. If you are using Mac or Linux, the gateway can be verified 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 192.0.0.249 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 fe80:984c:bf46:d4b7:b532%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): {169.93.114.162, 194.26.115.143}
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 0d:1b:4d:f4:e6:aa
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:b1:18:d8:ca:f9
}
How to Troubleshoot Connectivity Issues
When it comes to transferring data at the physical and data layer, you may encounter problems with either wired or wireless (Wi-Fi) connections to your router.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you’re using OSX or macOS, whether it’s version 10.11.6, 11.3.8, or 12.1.1, there are various tools available for troubleshooting. However, these tools do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes beneficial, especially for remote work and Work From Anywhere (WFA) teams.
Useful Built-in Scripts
One incredibly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings via the command line interface (CLI) and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool offers a more comprehensive range of logs, although many are only relevant to a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will produce logs in the /var/tmp/<blah>.tar.gz file. If you prefer to run it interactively (even though there’s not much interaction), you can use sudo /usr/bin/sysdiagnose and 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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