How To Troubleshoot Mac Internet
Explanation of Internet Addressing
When connecting to the internet, you are assigned a Public IPv4 address such as 79.163.40.171 or an IPv6 address like 2000:57fb:c291:5e95:ed2a:c116:43fc:4e32. These addresses can be verified at https://test-ipv6.com/. However, for those not well-versed in technology, conveying these addresses or even referencing MAC addresses such as 9b:fb:a4:15:ea:20 can be prone to errors and quickly become convoluted. In addition, the lack of historical data further complicates matters, especially when troubleshooting past issues.
Navigating the Internet
To access a website such as https://willms.info, the process begins with contacting a DNS server to convert the host portion (willms) and the Top Level Domain (info) of the URL into an IP address like 197.54.109.160. Every web request made by a computer and browser includes its type, such as Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
The Significance of Default Gateways
Typically, default gateways are automatically assigned addresses through DHCP. These gateways, such as 192.168.226.7, typically end in .1 or .254 based on the scope size. This is where a computer sends all of its traffic to be routed to its intended destination. For IPv6 connectivity troubleshooting, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/. Additionally, on Mac or Linux systems, the connectivity status can be verified with the commands provided.
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 192.168.226.7 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 fe80:3ff1:e15c:6ae7:4ab9%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): {158.221.53.219, 245.221.121.21}
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 9b:fb:a4:15:ea:20
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 ac:54:66:70:04:bd
}
Addressing Wired and Wireless Connectivity Issues
In the process of transmitting data to your router, you may utilize either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Technical Issues on Apple macOS / OSX Platforms
Regardless of whether your system is running on OSX/macOS versions such as 10.11.5, 11.3.3, or 12.3.9, there exists a wide array of tools available for troubleshooting. However, these manual measures and scripts do not provide a set of correlated values over a period of time. This is where automated remote troubleshooting becomes crucial, especially for teams operating in remote and Work From Anywhere (WFA) setups.
Utilizing Pre-installed Scripts for Assistance
One particularly useful tool on OSX/macOS is the sudo wdutil info command, which offers a dump of the current wireless settings to the CLI and can be configured to produce specific logs for troubleshooting purposes. Additionally, the more comprehensive sysdiagnose tool can generate a multitude of logs (although much of it is only relevant to wireless networks, similar to wdutil).
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz. For an interactive run (although there is minimal interaction), you can execute the sudo /usr/bin/sysdiagnose command, which will trigger a privacy warning. When not run in the background, it should open Finder in the correct location, allowing you to locate the logs in /var/tmp or use Finder with Cmd+Shift+G to navigate to the path. Keep in mind that the file sizes can be around 300MB, give or take.
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