Fix MacOS Internet Connection
The Fundamentals of Internet Addressing
When using the Internet, individuals may have a public IPv4 address, such as 90.110.146.220, or an IPv6 address, like2000:2467:a3b0:e72f:c91b:81d4:763e:e3fe. These addresses can be checked using https://test-ipv6.com/. However, for those not well-versed in technology, communicating and using addresses like these, or even referring to MAC addresses such as 47:67:e1:55:c4:5f, can quickly become complicated and error-prone. Furthermore, they do not provide any historical data, particularly from previous issues.
Navigating the Web and the Mechanics of Lookups
When accessing a webpage like https://rosenbaum.info, users first reach out to a DNS server to convert the host part (rosenbaum) and the Top Level Domain (info) of the URL into an IP address, such as 213.155.43.155. Additionally, all web requests from a user’s computer and browser include information about their type, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
Typically, default gateways are automatically configured addresses through DHCP. Users will receive a default gateway, such as 192.0.0.106 (usually ending in .1 or .254, depending on the scope size), to which their computer will send all its traffic to be further routed. For a more extensive guide on IPv6, visit how-to-fix-ipv6-connectivity/, or check on Mac or Linux using the following command:
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 192.0.0.106 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 fe80:26f9:f16f:6656:2595%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): {74.198.16.231, 10.231.250.105}
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 47:67:e1:55:c4:5f
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 f8:f9:d7:49:cf:aa
}
Resolving Connection Issues for Wired and Wireless Setups
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are running OSX or macOS versions such as 10.15.7, 11.4.5, or 12.3.3, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for teams operating remotely and embracing the concept of Work From Anywhere (WFA).
Utilizing Built-in Scripts and Commands for Assistance
One particularly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant at a specific point in time in relation to wireless, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive approach, you can run sudo /usr/bin/sysdiagnose, which will display 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. Keep in mind that the file sizes will be around 300MB more or less.
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