How Do You Troubleshoot MacOS Connectivity
How Internet Addressing Functions
When using the Internet, your device may have a Public IPv4 address, such as 181.2.100.130, or an IPv6 address like 2000:a2a6:b447:d608:ae13:93c7:e1ab:a2e1. You can verify this by visiting https://test-ipv6.com/. However, for individuals who are not tech-savvy, conveying these addresses or MAC addresses like e2:2a:e6:10:83:14 can be prone to errors and quickly becomes complex. Moreover, it does not provide historical data, especially when past issues occurred.
Navigating the World Wide Web
In order to visit a web page such as https://parker.com, you initially connect to a DNS server to convert the host portion (parker) combined with the Top Level Domain (com) of the URL into an IP address like 11.235.108.71. Your computer and browser always include its type with all web requests, for instance:
<br>Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Your default gateway is typically an automatically provided address through DHCP. It may be a default gateway like 192.168.88.113 (although they typically end in .1 or .254 depending on the scope size) where your computer sends all traffic to be routed onwards. For IPv6, there is a comprehensive guide available on how-to-fix-ipv6-connectivity/, but you can also 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 192.168.88.113 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:d622:a11a:80e6:e914%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): {226.187.34.79, 226.55.248.47}
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 e2:2a:e6:10:83:14
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 10:04:64:e5:ea:b1
}
Finding Solutions for Wired and Wireless Connectivity Issues
Whether you are using a wired or wireless (Wi-Fi) medium at the physical and data layer to transmit data to your router, troubleshooting connectivity issues is essential.
Navigating Apple macOS / OSX for Solutions
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.5, 11.1.3, or 12.3.7, there are numerous tools available for troubleshooting. However, these tools do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are accustomed to remote work and working from any location.
Utilizing In-Built Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info, which offers a dump of current wireless settings to the CLI, and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be utilized to generate a variety of logs, although much of it is only relevant to wireless settings at a given 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. For an interactive experience, you can runsudo /usr/bin/sysdiagnose and it 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 or use Finder with Cmd+Shift+G to navigate to the location. However, be cautious of file sizes, which can be around 300MB.
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