How To Fix OSX Issues
Understanding the Concept of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 110.126.96.241, or an IPv6 address, like 2000:96ae:128d:3a2d:3ead:48a2:2a9b:1a6f. You can verify this information at https://test-ipv6.com/. However, conveying these addresses to individuals who are not technically inclined can be prone to errors and can become complex. Moreover, this method does not offer any historical data, especially when dealing with past issues.
Navigating the World Wide Web
In order to access a website such as https://schultz-mayer.com, you initially connect to a DNS server to translate the host portion (schultz-mayer) along with the Top Level Domain (com) of the URL into an IP address, such as 175.17.225.209. Your computer and browser send its type with all web requests, 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
Exploring the Significance of Default Gateways
By default, your gateway is automatically configured via DHCP and you are provided with an address, such as 192.0.0.77 (although they typically end in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, a thorough guide can be found at how-to-fix-ipv6-connectivity/, and it can be checked on Mac or Linux using the following commands:
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 192.0.0.77 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 fe80:5e8a:b997:550a:7d05%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): {220.17.213.12, 134.9.214.175}
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:09:9b:8c:e6:a0
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 a3:5d:9c:f4:99:03
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are running OSX/macOS version 10.14.9, 11.2.3, or 12.0.1, 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 invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of 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 many of them are only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and 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 sudo /usr/bin/sysdiagnose, which will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to the path /var/tmp using Finder with Cmd+Shift+G. It’s important to note that the file sizes are approximately 300MB.
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