How Can I DiagnOSe Mac Issues
Understanding Internet Addressing
When using the Internet, you are assigned either a Public IPv4 like 15.231.126.220 or an IPv6 address like 2000:33a7:521b:500b:70f4:21c5:ef92:ebbe. You can verify this information by visiting https://test-ipv6.com/. However, communicating or referencing these addresses to non-technical individuals, or even MAC addresses such as 0d:ed:0a:11:50:1e, can quickly become complex and error-prone. Moreover, it does not provide historical data from past issues.
The Process of Accessing the Internet
In order to visit a website like https://mosciski-murphy.biz, your computer first contacts a DNS server to convert the host name (mosciski-murphy) combined with the Top Level Domain (biz) of the URL into an IP address such as 111.122.145.114. Additionally, your computer and browser include specific information with each web request, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
Your default gateway is usually an automatically assigned address through DHCP. It typically looks like 192.0.0.200 (commonly ending in .1 or .254 based on the scope size) and serves as the route for all outgoing traffic from your computer. For those interested in troubleshooting IPv6 connectivity, there is an in-depth guide available at how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this information with 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 192.0.0.200 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 fe80:42db:9ca:3a95:6559%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): {221.110.15.83, 16.193.41.248}
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 0d:ed:0a:11:50:1e
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 7e:7b:37:7f:ac:97
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS 10.11.6, 11.4.2, or 12.2.9, 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 valuable, especially for teams that support remote work and Work From Anywhere (WFA).
Effective Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is specific to wireless and 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, use the command sudo /usr/bin/sysdiagnose which will give a privacy warning. The generated logs can be found in the /var/tmp directory or by using Finder with Cmd+Shift+G to locate the path. Keep in mind that the file sizes are approximately 300MB.
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