Troubleshoot Apple Internet Connection
Understanding Internet Addressing Systems
When using the Internet, you are assigned a public IPv4 address, such as 153.237.164.8, or an IPv6 address, like 2000:8571:70f1:c1dc:ef07:d4bb:56ce:49da. These addresses can be verified using https://test-ipv6.com/, but conveying them accurately, especially for non-technical individuals, can be challenging. Furthermore, historical data about previous issues is not readily available.
Navigating the World Wide Web
Accessing a website, such as https://zulauf.com, involves initiating communication with a DNS server to convert the URL’s host portion (zulauf) and Top Level Domain (com) into an IP address, like 165.146.171.241. Each web request also includes the type of computer and browser being used, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically an address automatically assigned through DHCP, like 192.168.72.116 (usually ending in .1 or .254 depending on the scope size). This is the point to which your computer sends all traffic for further routing. A more in-depth discussion on IPv6 connectivity can be found at how-to-fix-ipv6-connectivity/ with instructions for Mac or Linux users.
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 192.168.72.116 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 fe80:783c:4027:84e0:3277%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): {180.227.17.44, 43.221.10.193}
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 b1:18:12:68:d8:22
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 f1:4e:4a:43:db:79
}
Fixing Connectivity Issues: Wired vs Wireless
When it comes to the physical and data layer, the choice between using a wired or wireless (Wi-Fi) medium to send data to your router can impact troubleshooting and fixing connectivity issues.
Resolving Problems on Apple macOS / OSX
Regardless of whether you are running OSX or macOS version 10.15.9, 11.2.8, or 12.1.8, there are various troubleshooting tools available. 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 engaged in remote work and Work From Anywhere (WFA) arrangements.
Using Built-in Scripts for Assistance
A valuable tool on OSX/macOS is the sudo wdutil info, which provides a dump to the Command Line Interface (CLI) of current wireless settings and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive approach by generating a wide range of logs, although many are only relevant to wireless at a specific point in time, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose and it will provide a privacy warning. Running it in the background should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to specify the path. Keep in mind that the file sizes are approximately 300MB.
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