How To Fix OSX Connectivity
Understanding Internet Addressing
In the world of the Internet, you are assigned a Public IPv4 address such as 207.193.206.252 or an IPv6 address like 2000:758a:843d:91d5:c1ac:7dc6:cdaf:cb5a. This can be verified from https://test-ipv6.com/. However, conveying these addresses, or even referencing MAC addresses like ef:76:a9:f5:7e:64, can be error-prone and complex, especially for those not familiar with technology. Also, this method lacks historical data, which is essential for troubleshooting past issues.
Navigating the World Wide Web
When you want to visit a website like https://cruickshank.info, your computer first contacts a DNS server to convert the host portion (cruickshank) combined with the Top Level Domain (info) of the URL into an IP address like 98.66.132.207. Your computer and browser provide their specifications with every web request, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Understanding the Significance of Default Gateways
By default, your gateway address is automatically configured through DHCP, resulting in an address like 192.0.0.121 (although they typically end in .1 or .254 based on the scope size). This is where your computer directs all its traffic to be forwarded. For IPv6, you can gain a comprehensive understanding from how-to-fix-ipv6-connectivity/ but you can run a 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 192.0.0.121 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:f759:35b9:17ad:b3bb%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): {136.106.255.217, 104.53.96.207}
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 ef:76:a9:f5:7e:64
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 46:7a:3f:56:ef:46
}
How to Troubleshoot and Solve Connectivity Issues
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) connection at the physical and data layer.
Tips for Diagnosing Problems on Apple macOS / OSX
Regardless of the version of macOS or OSX you’re using - whether it’s 10.13.5, 11.2.5, or 12.0.8 - there are various methods for troubleshooting connection issues. However, the manual actions and scripts available don’t provide a set of correlated values over time, which is where automated remote troubleshooting becomes useful, especially for remote and Work From Anywhere (WFA) teams.
Useful Built-in Tools
One helpful 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. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to wireless issues, though these are primarily point-in-time snapshots similar to wdutil.
You can run sudo nohup /usr/bin/sysdiagnose -u & in the background to generate logs at /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (even though there’s not much interaction), you can run
sudo /usr/bin/sysdiagnose and it will prompt a privacy warning. When 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 aware that the file sizes will be around 300MB or so.
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