How Do You Understand MacOS Connectivity
The Basics of Internet Addressing
When using the Internet, you will be assigned either a Public IPv4 address (e.g. 133.9.155.221) or an IPv6 address (e.g. 2000:c0a2:68:c22d:49cd:202f:bb7c:e73c). To verify your address, visit https://test-ipv6.com/. However, relaying these addresses, or even MAC addresses like e1:d0:6b:d6:ad:ed, to those unfamiliar with technology can be error-prone and complex. In addition, this information does not provide any historical data, particularly from previous incidents.
Navigating the World Wide Web
When accessing a web page such as https://steuber-cruickshank.name, you start by accessing a DNS server to convert the host portion (steuber-cruickshank) and the Top Level Domain (name) of the URL into an IP address, such as 251.58.61.99. Your computer and browser automatically send their type with all web requests, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Understanding the Significance of Default Gateways
Your default gateway is typically an address configured automatically through DHCP. This default gateway, such as 192.168.183.74 (although they usually end in .1 or .254 depending on the scope size), is where your computer sends all of its traffic to be routed forward. For IPv6, a comprehensive guide on how to fix IPv6 connectivity is available, but you can also check this 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 192.168.183.74 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 fe80:40b7:7674:a20e:e675%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): {0.153.173.46, 207.76.141.203}
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 e1:d0:6b:d6:ad:ed
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 15:06:88:7c:29:a1
}
Resolving Issues with Wired or Wireless Connectivity
Whether you are using a wired or wireless (Wi-Fi) medium to transmit data to your router, issues can arise at the physical and data layer.
Addressing Problems on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, be it 10.13.5, 11.2.2, or 12.2.4, 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 valuable, particularly for teams embracing remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the command line interface and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, albeit many are only point-in-time related to wireless, similar to how wdutil functions.
The command sudo nohup /usr/bin/sysdiagnose -u & can be used to run sysdiagnose in the background, writing logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. Running it without being in the background should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are around 300MB, more or less.
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