How To Test OSX No-access
Understanding IP Addressing
When using the Internet, you are assigned an IP address, such as 103.68.224.248 for IPv4 or 2000:1857:9896:8112:5cf8:25e2:14db:49da for IPv6. You can verify this information at https://test-ipv6.com/. However, for those not well-versed in technical jargon, communicating these addresses or MAC addresses like 49:6b:0e:32:c0:65 can be prone to mistakes and quickly becomes complex. Furthermore, this method does not provide historical data, making it difficult to troubleshoot past issues.
Navigating the World Wide Web
Accessing a website, such as https://heidenreich.co, begins with contacting a DNS server to convert the host portion (heidenreich) and the Top Level Domain (co) of the URL into an IP address, such as 39.157.185.64. Whenever your computer and browser make web requests, they include their type, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
Default gateways are usually automatically assigned addresses through DHCP. This gateway, such as 192.168.37.30 (typically ending in .1 or .254 depending on the scope size), is where your computer directs all its traffic for routing. For IPv6 connectivity issues, a comprehensive guide is available at how-to-fix-ipv6-connectivity/, and you can check on Mac or Linux with:
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 192.168.37.30 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 13f8:98:4e24:e880:41b8:1270:b33e:7d33%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): {14.13.118.150, 4.175.178.252}
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 49:6b:0e:32:c0:65
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 b7:a8:c6:f3:fe:17
}
Fixing Connectivity Issues with Wired or Wireless Networks
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Issues on Apple macOS / OSX Systems
Regardless of the version of OSX/macOS you are using, whether it’s 10.11.1, 11.4.3, or 12.3.4, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that are into remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
On OSX/macOS, the sudo wdutil info tool is quite useful as it provides a dump to the CLI of current wireless settings and can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be used to generate a wide variety of logs, although the majority of the information pertains to a specific point in time, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose but be mindful of the file sizes, which are approximately 300MB or more.
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