How Do You DiagnOSe OSX Issues
Explanation of Internet Addressing
When using the Internet, it is possible to have a Public IPv4 address, such as 225.216.6.134, or an IPv6 address, such as 2000:27a4:522:1f2c:e300:81bc:3812:4eb4. Verification of these addresses can be done at https://test-ipv6.com/. However, attempting to explain and convey these addresses to non-technical individuals, as well as referencing MAC addresses like b2:32:ca:05:b5:2e, can be prone to errors and become complex. Furthermore, it does not provide any historical data, particularly in regard to previous problems that have occurred.
How to Access the Internet
When wishing to visit a web page like https://hermann.info, the initial step involves accessing a DNS server to convert the host portion (hermann), combined with the Top Level Domain (info) of the URL, into an IP address, such as 171.80.162.240. During all web requests, your computer and browser sends its type, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
The default gateway is usually an address configured automatically via DHCP. This default gateway, which typically ends in .1 or .254 depending on the scope size, such as 172.28.49.8, is where your computer sends all of its traffic to be routed onwards. For those interested in more information on IPv6, a detailed explanation can be found at how-to-fix-ipv6-connectivity/, while checking on Mac or Linux can be done using the following command:
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 172.28.49.8 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 fe80:1408:9954:bf27:5a51%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): {105.58.71.68, 235.0.7.59}
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 b2:32:ca:05:b5:2e
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 83:c4:5a:a3:18:6a
}
Resolving Connectivity Issues with Wired and Wireless Networks
When it comes to the physical and data layers, you might be utilizing a wired or wireless (Wi-Fi) medium to transmit data to your router.
Troubleshooting on Apple macOS / OSX Versions
Regardless of whether you are using OSX/macOS versions such as 10.14.6, 11.5.8, or 12.0.4, there are various tools available for fixing connectivity issues. However, these 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 embrace remote work and Work From Anywhere (WFA).
Effective Built-in Utilities
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and it can also be configured to produce specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to wireless issues, although much of it is only relevant at a specific point in time, 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, you can execute sudo /usr/bin/sysdiagnose which will give a privacy warning. If 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 will be around 300MB or slightly more.
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