Understand MacOS Internet
Understanding Internet Addressing
When using the Internet, you are assigned a unique identifier, known as an IP address. This can be in the form of a Public IPv4 address like 239.131.91.65 or an IPv6 address like 2000:f996:592c:6850:4166:a044:d651:f59a. To check your IP address, you can visit https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses or even identifying MAC addresses like 8f:82:fb:fe:73:c4 can be prone to error and quite complex. Furthermore, it does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
Accessing a website such as https://beier.io involves the use of a DNS server to translate the URL’s host portion (beier) and Top Level Domain (io) into an IP address like 219.159.20.170. Additionally, your computer and browser send their specific type with all web requests, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
Understanding the Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. This gateway, such as 10.73.83.21 (usually ending in .1 or .254 based on the scope size), is where your computer sends all its traffic to be forwarded onwards. For IPv6, detailed instructions can be found in our post on how-to-fix-ipv6-connectivity/, and you can verify it 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 10.73.83.21 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:bfd8:e50a:eb58:8f07%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): {143.1.178.179, 99.201.167.224}
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 8f:82:fb:fe:73:c4
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 45:24:e0:1a:cb:4b
}
Resolving Connection Issues for Wired and Wireless Networks
When transmitting data to your router, you may encounter issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are running versions 10.13.6, 11.6.7, or 12.1.2 of OSX/macOS, there are various troubleshooting tools at your disposal. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless-related settings to the CLI and can be configured to generate specific logs for troubleshooting. Alternatively, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only related to the wireless settings at a certain point in time, similar to wdutil.
To run this tool in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, which will provide a privacy warning. When not run in the background, the logs will open in Finder, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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