How To DiagnOSe Mac Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 135.6.138.142 or 2000:e0b4:287d:5cd2:a68a:cbc:9233:4738. You can verify your address at https://test-ipv6.com/. However, describing and communicating these addresses, along with MAC addresses like ec:49:fd:ad:37:5e, can be challenging and error-prone for non-technical individuals. It also lacks historical data, especially for past issues.
Navigating the Internet
When accessing a website like https://adams.info, your computer queries a DNS server to convert the host (adams) and Top Level Domain (info) of the URL into an IP address, such as 126.230.11.165. Additionally, your computer and browser include its type in all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
Your default gateway is typically assigned automatically through DHCP and may be a numerical address like 172.29.15.67. This is where your computer directs all its traffic for further routing. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available, and it can also be verified 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 172.29.15.67 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 fe80:711:af7:efba:2d8f%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): {135.44.117.63, 132.168.162.200}
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 ec:49:fd:ad:37:5e
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 20:83:6c:4e:c1:d1
}
Identify and Resolve Connectivity Issues
When it comes to transmitting data to your router, you may be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of the version of OSX/macOS you are running, whether it’s 10.13.2, 11.0.6, or 12.2.2, there are various troubleshooting tools available. However, the manual actions and scripts do not provide a series of correlated values over time, which makes automated remote troubleshooting particularly beneficial for teams that practice remote work and Work From Anywhere (WFA).
Utilize Pre-Installed Scripts
A useful tool on OSX/macOS is sudo wdutil info, which allows you to obtain a dump of current wireless settings via the CLI and can be configured to generate specific troubleshooting logs. For more comprehensive logs, the sysdiagnose tool is also available, although it primarily captures point-in-time information related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. For an interactive experience (albeit with limited interaction), you can run sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind the file sizes, which are approximately 300MB.
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