How To Understand MacOS Issues
The Functioning of Internet Addressing
When using the Internet, you may have a Public IPv4 address similar to 138.106.121.147 or an IPv6 address such as 2000:1582:4b0c:8d9c:95c7:885a:383f:1cdf. You can verify this by visiting https://test-ipv6.com/. However, explaining these addresses, as well as MAC addresses like de:d7:98:fc:7a:6b, to those not well-versed in technology can be prone to errors and can become complex rather quickly. Moreover, this information does not provide any historical data, particularly from previous issues.
Navigating the Internet
When reaching a website like https://rodriguez.info, the first step involves accessing a DNS server to convert the host portion (rodriguez) along with the Top Level Domain (info) of the URL into an IP address, such as 206.107.228.231. Your computer and browser sends its type with all web requests, for example:
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
Typically, your default gateway is an automatically assigned address via DHCP. It is usually a default gateway like 192.0.0.17 (although they often end in .1 or .254 based on the scope size) where your computer directs all its traffic to be further routed. For IPv6, a comprehensive overview is available at how-to-fix-ipv6-connectivity/, and you can verify 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 192.0.0.17 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 fe80:435e:42d2:4fc3:aa86%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): {142.138.179.67, 107.113.164.220}
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 de:d7:98:fc:7a:6b
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 99:59:1a:2e:8d:35
}
Resolve Wired and Wireless Connectivity Issues
When it comes to transferring data to your router, you might be using a wired or wireless (Wi-Fi) connection at the physical and data layer.
Steps to Take on Apple’s macOS / OSX
No matter which version of OSX/macOS you’re using, whether it’s 10.12.9, 11.0.9, or 12.1.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
A handy tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it only pertains to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can runsudo /usr/bin/sysdiagnose, which 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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