How Do You Understand OSX Connectivity
Understanding IP Addressing
When connecting to the Internet, you are assigned a Public IPv4 address such as 102.1.101.13 or an IPv6 address like 2000:74eb:1324:cec3:2e7a:2486:48a1:df8f. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses, or even MAC addresses like e6:4b:05:d9:22:c6, to individuals without technical knowledge can lead to errors and complexity. Furthermore, this method does not provide historical data, especially regarding past issues.
Navigating the Internet
When attempting to access a web page, such as https://prosacco-emard.com, your device first communicates with a DNS server to convert the host portion (prosacco-emard) along with the Top Level Domain (com) of the URL into an IP address, for example, 102.81.201.107. Every web request made by your computer and browser includes its type, which can be something like Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. This gateway, such as 10.126.232.247 (although it typically ends in .1 or .254 based on the scope size), is where your computer directs all of its traffic to be forwarded. We offer an in-depth guide on how-to-fix-ipv6-connectivity/ for IPv6, and on Mac or Linux, you can check by 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 10.126.232.247 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:daec:87ae:7e74:a252%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): {109.33.109.137, 237.110.137.2}
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 e6:4b:05:d9:22:c6
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 a2:95:96:4f:13:ab
}
Solve Connectivity Issues with Wired or Wireless Network
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Strategies for Troubleshooting on Apple macOS / OSX
Irrespective of whether you are running OS X/macOS 10.11.7, 11.5.4, or 12.0.6, there is a wide array of troubleshooting tools available. However, the 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 that are embracing remote work and Work From Anywhere (WFA) culture.
Embedded Command-Line Tools for Assistance
An incredibly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a comprehensive range of logs, although much of it is only point-in-time data related to wireless, similar to wdutil.
Executing sudo nohup /usr/bin/sysdiagnose -u & will run the tool in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (although there isn’t much interaction involved), you can use the command sudo /usr/bin/sysdiagnose, which will trigger a privacy warning. When not run in the background, it should open Finder in the correct location, or you can manually navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. However, be cautious of the file sizes, which can be around 300MB.
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