How Do You DiagnOSe Mac Internet Connection
Understanding Internet Protocol Addresses
When using the Internet, it is common to have a unique identifier known as an IP address. This can come in the form of a Public IPv4 address, such as 148.44.212.74, or an IPv6 address, like 2000:de7c:8b0b:f9ef:e46e:95f2:a8ca:fc96. You can check your IP address at https://test-ipv6.com/. However, these addresses can be difficult for non-technical individuals to communicate effectively, and the inclusion of MAC addresses only adds to the complexity. Furthermore, historical data about previous issues is not readily available.
Navigating the Internet
Accessing a website, such as https://lemke.co, involves the use of a DNS server to translate the URL into an IP address, such as 126.238.81.117. Your computer and browser also send specific information with each web request, as indicated by the user agent string: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
The default gateway, typically obtained through automatic DHCP configuration, is a crucial component of network connectivity. Whether it is an address like 10.171.178.200 for IPv4 networks or a more complex setup for IPv6, the default gateway is where your computer sends all its traffic to be routed onwards. For specific troubleshooting information on IPv6 connectivity, detailed instructions are available at how-to-fix-ipv6-connectivity/. Additionally, Mac and Linux users can utilize specific commands to check their network configurations.
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 10.171.178.200 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 fe80:6556:756b:97b8:d492%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): {40.87.54.123, 121.113.71.147}
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 37:1c:2f:08:e4:0a
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 91:87:14:04:5b:e0
}
Fixing Connectivity Issues with Wired and Wireless Networks
When it comes to transferring data to your router, you have the option to 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 10.15.8, 11.4.4, or 12.2.2, there are numerous troubleshooting tools available. However, these manual actions and scripts fail to provide a set of interconnected values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA) policies.
Useful Built-in Scripts for Troubleshooting
One highly useful tool for OSX/macOS users is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be set up to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool offers even more comprehensive log generation capability (although most of it is related to wireless settings at a specific point in time, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will produce logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there isn’t much interaction), you can use the command sudo /usr/bin/sysdiagnose but be prepared for a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp and use Cmd+Shift+G to direct Finder to the path. However, be mindful of the file sizes, which are typically around 300MB.
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