Understand OSX Connectivity
Understanding Internet Addressing
In the realm of the Internet, individuals are assigned unique IP addresses, such as the typical Public IPv4 address 31.20.126.70 or the newer IPv6 address 2000:be61:9fbb:3d6e:5135:9a30:1b8f:e12b. These addresses can be verified on https://test-ipv6.com/. However, conveying these addresses, and even referring to MAC addresses like ee:c9:11:f7:2d:d5, can be challenging for those less familiar with technical jargon. This becomes even more complex and prone to errors when dealing with historical data.
Navigating the World Wide Web
In order to reach a particular web page, such as the example of https://koelpin.org, users first tap into a Domain Name System (DNS) server to map the host segment (koelpin) along with the Top Level Domain (org) of the URL to an IP address such as 182.171.138.251. Notably, every web request from a computer and browser includes its own specific type, for instance Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285.
Significance of Default Gateways
The default gateway is typically assigned automatically through DHCP and is denoted by an address like 192.168.179.115 (commonly ending in .1 or .254 based on the scope size). This gateway serves as the point through which a computer forwards all of its data to be routed further. For a detailed analysis of default gateways for IPv6, refer to the resource how-to-fix-ipv6-connectivity/, or verify on Mac or Linux by executing:
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 192.168.179.115 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:f6bf:47d7:b3a8:67b%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): {247.160.196.125, 53.227.0.201}
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 ee:c9:11:f7:2d:d5
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 1e:72:b6:d9:99:f0
}
Resolving Connection Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter the version of OSX/macOS you are running - whether it’s 10.14.3, 11.5.4, or 12.3.8 - there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although most are only relevant to wireless at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run (even though there is not much interaction), use sudo /usr/bin/sysdiagnose and it will display a privacy warning. Running it in the foreground should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. Be mindful of the file sizes, which are typically around 300MB.
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