How Can I Troubleshoot MacOS Internet
Understanding the Functionality of Internet Addressing
When using the Internet, you will be assigned either a Public IPv4 address (e.g. 247.78.148.144) or an IPv6 address (e.g. 2000:4908:82b7:3f55:a551:13b8:628f:8847). The verification of these addresses can be done on https://test-ipv6.com/. However, for those who are not tech-savvy, communicating and referencing these addresses, as well as MAC addresses such as b7:07:18:89:ca:70, can be prone to errors and quickly become complicated. Moreover, this does not provide any historical data, especially from previous problems that may have occurred.
Initiating Web Connections
When trying to access a web page like https://casper-vandervort.com, the first step involves reaching a DNS server to convert the host portion (casper-vandervort) combined with the Top Level Domain (com) of the URL into an IP address, such as 97.162.30.215. Your computer and browser send their type with all web requests, such as: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP. It could be a default gateway like 192.0.0.32 (although they usually end in .1 or .254 depending upon the scope size) and it is the destination where your computer sends all its traffic to be routed onwards. For IPv6, you can find more information on how-to-fix-ipv6-connectivity/ or you can 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 192.0.0.32 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 fe80:95e1:8ea4:d672:ee91%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): {135.92.152.165, 12.6.98.70}
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 b7:07:18:89:ca:70
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 1f:41:23:bc:d1:d1
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you’re using, whether it’s 10.12.3, 11.1.5, or 12.1.7, there are various tools available for troubleshooting. However, these manual actions and scripts don’t provide a series of correlated values over time. This is where automated remote troubleshooting is particularly useful, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info, which dumps current wireless-related settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide variety of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, you can run it in the background and it will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can run
sudo /usr/bin/sysdiagnose which will give 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 to point Finder to the path. Keep in mind that the file sizes are approximately 300MB more or less.
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P.S. Tips For Remote Network and Client Support
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