How To Troubleshoot OSX No-access
The Fundamentals of Internet Addressing
When using the Internet, individuals may have a unique Public IPv4 address such as 226.39.202.58 or an IPv6 address like 2000:e783:20bc:2856:3382:b622:f3d1:60d2. We can verify this using the tool https://test-ipv6.com/. However, for those who are not tech-savvy, conveying these addresses or even mentioning MAC addresses such as 89:89:e8:e6:82:c1 can be prone to errors and become complicated quickly. Furthermore, this method does not provide any historical data, especially from previous incidents.
Navigating the Internet
When trying to access a website like https://witting-spinka.co, the first step is to connect to a DNS server to convert the host portion (witting-spinka) combined with the Top Level Domain (co) of the URL into an IP address like 38.31.119.167. With every web request, your computer and browser also send its type, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding Default Gateways
The default gateway is typically an automatically configured address through DHCP. You obtain a default gateway like 192.168.85.75 (although they commonly end in .1 or .254, depending on the scope size), and this is where your computer sends all its traffic to be routed onwards. For IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/ although you can also check on Mac or Linux by:
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 192.168.85.75 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:d4be:b819:97fe:cba7%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): {4.213.175.102, 254.139.172.252}
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 89:89:e8:e6:82:c1
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 e2:a0:56:8d:f5:d0
}
Resolving Issues with Wired and Wireless Connections
When dealing with the physical and data layer, it’s important to keep in mind the various troubleshooting methods for both wired and wireless (Wi-Fi) mediums used to transmit data to the router.
Strategies for Apple macOS / OSX Users
Regardless of the OSX/macOS version you’re operating on, whether it’s 10.15.5, 11.5.7, or 12.3.9, there are numerous tools available for troubleshooting. However, these manual actions and scripts fall short when it comes to providing a series of correlated values over time. This is where automated remote troubleshooting becomes especially valuable, particularly for teams engaged in remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
A useful built-in tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings via the CLI, and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although much of the data is only relevant to wireless networks, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. For an interactive experience (although there isn’t much interaction), you can execute sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If 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 will be around 300MB, more or less.
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