How Do You Troubleshoot MacOS Internet
The Functioning of Internet Addressing Systems
When you connect to the Internet, you are assigned a specific IPv4 or IPv6 address. These addresses, such as 110.107.65.48 or 2000:5906:2ecf:c176:b30d:5167:5b14:5069, can be verified using the https://test-ipv6.com/ website. However, sharing these addresses, and even MAC addresses like b6:4d:4e:91:57:47, with individuals who are not well-versed in technology can lead to errors and complexities. Moreover, such information does not provide any historical context, particularly when addressing past issues.
Navigating the World Wide Web
When accessing a site such as https://hintz-rohan.io, your computer first contacts a DNS server to convert the URL’s host portion (hintz-rohan) and its Top Level Domain (io) into an IP address, for instance, 176.181.12.210. Additionally, all web requests sent by your computer and browser include its specifications, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
The Significance of Default Gateways
The default gateway, typically a DHCP-generated address, like 192.0.0.110 (often ending in .1 or .254 depending on the scope size), is where your computer directs all its outgoing traffic for routing. For IPv6, a comprehensive explanation can be found in our article how-to-fix-ipv6-connectivity/, yet on Mac or Linux, it can be verified using:
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 192.0.0.110 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 fe80:3cf2:3ba9:8a29:7c81%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): {90.140.170.43, 27.255.150.127}
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 b6:4d:4e:91:57:47
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 a4:bb:82:1b:af:82
}
Resolving Connectivity Issues in Wired and Wireless Networks
When transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Methods for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.11.7, 11.0.6, or 12.1.7, there are various tools available for troubleshooting. Unfortunately, the 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).
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use sudo /usr/bin/sysdiagnose and follow the instructions to access the generated logs. However, be mindful of the file sizes, which are typically around 300MB.
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