How To Understand MacOS Internet Connection
Explanation of Internet Addressing
When using the Internet, you will be assigned a Public IPv4 address such as 10.181.34.165 or an IPv6 address similar to 2000:c78e:9bf7:8293:65e0:603:a7cf:53e3. The validity of these addresses can be verified at https://test-ipv6.com/, however, explaining these addresses, as well as MAC addresses like 67:1f:d7:81:43:8d, to non-technical individuals can be prone to errors and become complex very quickly. In addition, there is a lack of historical data, particularly during previous issues.
Navigation of Web Pages
Accessing a web page, such as https://moen.io, involves the initial communication with a DNS server to transform the combined host portion (moen) and top level domain (io) of the URL into an IP address like 213.112.159.78. Furthermore, the computer and browser include their type with each web request, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. A typical default gateway is presented as 192.0.0.169 (usually ending in .1 or .254, depending on the scope size), and is responsible for routing all traffic from your computer. For IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/, where instructions for checking on Mac or Linux can be found.
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 192.0.0.169 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:aa45:e2fe:7236:974c%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): {38.207.162.177, 31.120.152.237}
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 67:1f:d7:81:43:8d
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 42:93:31:74:32:3c
}
Resolving Issues with 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.
Strategies for Addressing Problems on Apple macOS / OSX
Regardless of whether you are using OSX/macOS versions like 10.14.6, 11.3.6, or 12.2.8, there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, making it difficult to diagnose issues. This is where automated remote troubleshooting becomes essential, especially for teams working remotely and embracing the concept of Work From Anywhere (WFA).
Useful Built-in Commands
A very 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 generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs (although many are only relevant to a specific point in time, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be aware that the file sizes can be around 300MB.
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