How Do You Troubleshoot OSX Internet Connection
Understanding the Functioning of Internet Addressing
When you connect to the Internet, you are assigned a Public IPv4 address such as 47.94.148.168 or an IPv6 address like 2000:78a0:6c07:5741:cbdb:dd2f:4717:a1b5. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to those who are not familiar with technical terminology can be prone to errors and become complex. Moreover, this method does not provide historical data, particularly from previous issues.
Navigating the World Wide Web
When you visit a web page like https://johnson.io, you initially reach out to a DNS server to translate the host portion (johnson) combined with the Top Level Domain (io) of the URL into an IP address such as 29.195.88.252. Your computer and browser include specific information with every web request, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
Recognizing the Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. A default gateway like 10.9.98.186 is assigned (usually ending in .1 or .254 based on the scope size), and this is where your computer sends all its traffic to be directed onward. For IPv6, you can refer to a comprehensive guide on how-to-fix-ipv6-connectivity/, but you can also check this on Mac or Linux 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 10.9.98.186 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:e07a:736d:5595:5db8%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): {37.232.192.175, 159.15.102.43}
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 b5:ad:68:ea:86:1d
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 f1:90:4f:c3:f7:04
}
Troubleshooting Wired and Wireless Connections
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Issues on Apple macOS / OSX
Regardless of which version of OSX/macOS you’re running - whether it’s 10.15.1, 11.4.2, or 12.1.8 - there are a variety of tools available for troubleshooting. However, these manual actions and scripts don’t provide a set of correlated values over time. This is where automated remote troubleshooting comes into play, especially for teams that prioritize remote work and Work From Anywhere (WFA).
Helpful Built-in Scripts
One highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of 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 at specific points in time, much like wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (even though there isn’t much interaction), you can run sudo /usr/bin/sysdiagnose and it will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be aware of the file sizes, which are approximately 300MB or so.
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