Understand MacOS Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned an IP address like 202.191.51.253 for IPv4 or 2000:d447:bf9:e43d:cb68:1f49:6781:af93 for IPv6. You can verify this through https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even referencing MAC addresses like e1:72:26:8b:bb:66, can lead to errors and complexity. Furthermore, it does not provide any historical data, especially for past issues.
Navigating Through the Internet
To reach a website such as https://schoen.biz, you first access a DNS server to translate the host portion (schoen) along with the Top Level Domain (biz) of the URL to an IP address like 213.167.228.188. When making web requests, your computer and browser send their type, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is typically an address automatically configured via DHCP, such as 172.29.106.214 (although they usually end in .1 or .254 depending on the scope size), and serves as the point where your computer forwards all its traffic for routing. For IPv6, detailed instructions can be found in our guide on addressing IPv6 connectivity issues, but you can also check 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 172.29.106.214 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 fe80:7460:316f:70b4:f2a9%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): {233.175.88.56, 127.155.185.167}
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 e1:72:26:8b:bb:66
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 0d:02:92:9d:4e:41
}
Resolution of Issues with Wired or Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
How to Address Problems on Apple macOS / OSX
No matter which version of OSX/macOS you are operating on, whether it’s 10.12.8, 11.0.2, or 12.3.1, there is a variety of tools available for resolving issues. However, these tools, along with manual actions and scripts, do not provide a set 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).
Pre-Installed Scripts That Can Provide Assistance
A highly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the command line interface (CLI), and can be configured to 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 wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will save logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can executesudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Be cautious of the file sizes, which are approximately 300MB or more.
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