How Do You Understand MacOS Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned an IP address, such as 176.28.160.189 for IPv4 or 2000:8408:c20a:fa4f:90e0:baf7:2dbf:5048 for IPv6. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses and MAC addresses like 0f:4a:dc:de:ea:2b to those not well-versed in technology can be prone to error and quickly become complex. Furthermore, this information does not provide any historical data, especially regarding past issues.
Navigating the World Wide Web
When accessing a website such as https://goldner.net, your initial contact is with a DNS server to translate the host portion (goldner) and the Top Level Domain (net) of the URL into an IP address such as 161.45.86.72. Your computer and browser send this type of information with all web requests, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts).
The Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP, such as 10.2.58.241 (although they usually end in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, we offer an in-depth discussion on how-to-fix-ipv6-connectivity/, but you can also check 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 10.2.58.241 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 fe80:7e1d:694e:939e:eeec%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): {83.212.84.233, 169.138.173.170}
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 0f:4a:dc:de:ea:2b
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 60:46:15:6f:a1:ad
}
Solutions for Diagnosing and Resolving Connectivity Issues
Whether you are using a physical Ethernet connection or a wireless (Wi-Fi) medium to transmit data to your router, troubleshooting may be necessary to address any connectivity issues.
Tips for Managing Connectivity on Apple macOS / OSX
Regardless of your version of OSX/macOS, whether it’s 10.11.9, 11.2.3, or 12.1.3, there are various tools available for diagnosing and resolving connectivity issues. However, these manual actions and scripts may not provide a comprehensive 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).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a detailed overview of current wireless settings through the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the more comprehensive sysdiagnose tool can be used to generate a wide range of logs, although much of the information is only relevant to wireless issues, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, running it interactively will prompt a privacy warning, and the logs will be written to the specified directory. Be mindful of the file sizes, which can be around 300MB.
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