How Can I DiagnOSe MacOS Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address. These addresses can be verified at https://test-ipv6.com/. However, relaying these addresses to others, or even mentioning MAC addresses, such as f0:e2:9b:68:c2:ed, can be complex and prone to errors. Furthermore, it does not provide any historical data.
Navigating the Internet
In order to access a website, such as https://homenick.name, you first need to contact a DNS server to convert the host section (homenick) and the Top Level Domain (name) of the URL to an IP address like 237.185.54.124. Your computer and browser provide their specifications with each web request, 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
Understanding Default Gateways
The default gateway is typically an address assigned automatically via DHCP. This address, such as 10.142.213.27, serves as the central routing point for all outgoing traffic from your computer. For IPv6 troubleshooting tips, visit how-to-fix-ipv6-connectivity/ or use the following commands on Mac or Linux:
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 10.142.213.27 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:f549:f010:cd48:3509%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): {8.50.149.247, 62.211.126.23}
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 f0:e2:9b:68:c2:ed
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 f6:be:6d:ca:d4:ad
}
Resolving Connectivity Issues for Wired and Wireless Networks
When transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.12.8, 11.3.4, or 12.3.8, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
A very useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI. This 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 point-in-time data related to wireless, just like 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 &. If you prefer to run it interactively, use sudo /usr/bin/sysdiagnose, but be mindful of the large file sizes of about 300MB.
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