Troubleshoot OSX Internet
Functioning of Internet Addressing
When using the Internet, individuals may acquire a Public IPv4 address, such as 152.210.12.254, or an IPv6 address like 2000:430a:ab99:6f5a:e2e:63b7:e4ac:c2ec. This can be verified at https://test-ipv6.com/. Communicating these addresses or even citing MAC addresses like 06:27:74:2e:8b:fb can be prone to errors and becomes complex. Furthermore, it does not provide any historical data, particularly during previous incidents.
Navigating the Internet
To access a webpage, such as https://west.info, one initially contacts a DNS server to convert both the host portion (west) and the Top Level Domain (info) of the URL into an IP address, for example, 188.217.62.249. When making web requests, the computer and browser actually include information about its type, such as 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. For instance, a default gateway like 192.168.173.201 (usually ending in .1 or .254 depending on the scope size) is where all the computer’s traffic is sent to be routed further. For IPv6, a detailed analysis is available at how-to-fix-ipv6-connectivity/, but it can also be checked 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 192.168.173.201 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 fe80:3b8c:1e2a:eb9d:4791%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): {225.2.50.248, 124.191.101.136}
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 06:27:74:2e:8b:fb
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 a8:16:7a:02:52:d5
}
Solutions for Wired and Wireless Connectivity Issues
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.4, 11.6.9, or 12.3.3, there are various tools available for troubleshooting. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Scripts for Troubleshooting
On OSX/macOS, the sudo wdutil info tool is very helpful as it provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose tool, which can generate a variety of logs related to wireless issues (though most of it is point-in-time data, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool 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 with a privacy warning. When not run in the background, it will open Finder in the correct location, or you can navigate to /var/tmp and view the file sizes, which are usually around 300MB.
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P.S. Tips For Remote Network and Client Support
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