DiagnOSe OSX Issues
Explanation of Internet Addressing
When using the Internet, it’s common to have a unique IP address assigned. It could be a Public IPv4 address like 47.215.123.189 or the longer IPv6 address like 2000:25f1:66b6:5497:d73a:8bbf:7724:5858. You can verify this information at https://test-ipv6.com/. These addresses are often difficult to communicate, especially for those not familiar with tech jargon. Additionally, they do not provide historical data, which can be important when troubleshooting past issues.
Overview of Connecting to Websites
Accessing a website such as https://cremin-boyer.net involves the translation of the URL’s host portion (cremin-boyer) and its Top Level Domain (net) to an IP address like 138.116.145.63. Additionally, all web requests include information about your computer and browser type, for example:
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Significance of Default Gateways
A default gateway, usually obtained via DHCP, serves as the address used to route all traffic from your computer. This is typically a automatically configured address, such as 192.0.0.216 (commonly ending in .1 or .254 depending on the scope size). For those using IPv6, a more detailed guide on this topic can be found at how-to-fix-ipv6-connectivity/, and instructions for checking on Mac or Linux systems are also available.
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 192.0.0.216 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:dd5c:87fa:bfb4:f45e%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): {2.80.201.163, 90.240.34.202}
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 6e:19:f6:65:97:f1
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 31:b0:35:79:f4:df
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data, you might be utilizing either a wired or a wireless (Wi-Fi) medium at the physical and data layer to send the data to your router.
Troubleshooting on Apple macOS / OSX Systems
Irrespective of the version of OSX/macOS you have, whether it’s 10.13.4, 11.6.3, or 12.2.9, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Scripts for Troubleshooting
An effective tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a more comprehensive approach, generating a wide range of logs (although many are only relevant to wireless settings, similar to wdutil).
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, simply execute sudo /usr/bin/sysdiagnose, although it will issue a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp manually or using Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB.
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