How To Understand OSX Issues
Understanding How Internet Address Allocation Functions
When using the Internet, individuals are assigned a Public IPv4 code such as 109.173.70.63 or an IPv6 code like 2000:fc5d:9269:cb77:f935:b87f:aa98:900f. This information can be verified at https://test-ipv6.com/. Nevertheless, the process of conveying these codes to non-technical individuals, or even referencing MAC addresses like c2:2b:be:07:75:2e, is prone to mistakes and becomes complex rapidly. Furthermore, this method does not offer any historical data (particularly pertaining to previous issues).
Navigating the World Wide Web
In order to access a website such as https://senger-vandervort.org, the user initially contacts a DNS server to convert the host segment (senger-vandervort) in combination with the URL’s Top Level Domain (org) into an IP code like 210.5.201.24. It’s important to note that the computer and browser transmit their type alongside all web requests e.g. Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Recognizing the Significance of Standard Gateways
Ordinarily, the default gateway is an address that is automatically configured via DHCP. The default gateway comes in the form of 172.21.35.205 (although typically ending in .1 or .254 based on the scale) and this is where the user’s computer directs all traffic to be passed on. For IPv6, an in-depth explanation is provided in how-to-fix-ipv6-connectivity/, while Mac or Linux users can verify this by 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 172.21.35.205 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:cb03:97df:ade6:152e%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): {43.61.32.44, 17.215.239.108}
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 c2:2b:be:07:75:2e
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 1a:a8:bc:43:d3:ac
}
Fixing Connectivity Issues for Wired or Wireless Networks
When transmitting data to your router, you may use either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple’s macOS
Regardless of whether you are using OSX/macOS version 10.14.6, 11.3.6, or 12.2.6, there are various troubleshooting tools available. However, the manual actions and scripts may not provide a series of correlated values over time. This is where automated remote troubleshooting becomes especially valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Using Built-in Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the Command Line Interface (CLI) and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only point-in-time in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive mode, run sudo /usr/bin/sysdiagnose and follow the privacy warning. When not run in the background, it should open Finder in the correct location, but you can also navigate to /var/tmp using Cmd+Shift+G in Finder. Just be cautious of the file sizes, which are approximately 300MB.
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