How To DiagnOSe MacOS Internet
The Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 216.156.145.123, or an IPv6 address, like 2000:ea27:924d:d024:e96:971:515b:4250. This information can be verified at https://test-ipv6.com/. However, for those who are not tech-savvy, trying to relay these addresses, or even mention MAC addresses like 03:fb:85:bd:aa:59, can be prone to mistakes and become complex very quickly. Furthermore, this method does not provide any historical data, particularly regarding previous issues.
Navigating the World Wide Web
In order to access a web page like https://kreiger.co, you first connect to a DNS server to convert the host section (kreiger) combined with the Top Level Domain (co) of the URL to an IP address, such as 205.159.34.207. Whenever your computer and browser makes web requests, it actually includes its type, 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
The Significance of Default Gateways
The default gateway is typically an automatically allocated address through DHCP. You will receive a default gateway such as 192.0.0.99 (although they normally end in .1 or .254, depending on the scope size), and this is the point to which your computer redirects all its traffic for further routing. You can find a detailed examination of IPv6 connectivity at how-to-fix-ipv6-connectivity/, but you can also 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 192.0.0.99 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 fe80:9553:1a05:4990:3356%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): {176.189.92.211, 46.30.140.180}
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 03:fb:85:bd:aa:59
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 73:aa:24:92:5a:49
}
Resolving Issues with Wired and Wireless Connections
When sending data to your router, you may use either 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 versions like 10.14.7, 11.1.7, or 12.0.3, there are various troubleshooting tools available. Unfortunately, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes useful, especially for teams that are adopting remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
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 also 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 only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run (although there is minimal interaction), use the command sudo /usr/bin/sysdiagnose and be mindful of the large file sizes of approximately 300MB.
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