How To Test MacOS Issues
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 48.198.172.173, or an IPv6 address, like 2000:99ce:e181:8535:3e:1451:d1d0:cf5. These addresses can be checked at https://test-ipv6.com/. However, for those who are not technologically inclined, communicating or identifying these addresses, as well as MAC addresses like 6b:d6:d6:8c:2d:ec, can be error-prone and confusing. Moreover, historical data regarding previous issues is not provided.
Navigating the World Wide Web
Accessing a webpage, such as https://kuhlman-hickle.info, involves initially connecting to a DNS server to convert the host domain (kuhlman-hickle) combined with the Top Level Domain (info) of the URL to an IP address, like 227.74.54.241. In this process, your computer and browser transmit information about their type with every web request, such as:Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. It usually ends in .1 or .254, depending on the scope size, such as 10.248.221.30, and is where your computer sends all its traffic to be routed onwards. For more in-depth information on IPv6, refer to how-to-fix-ipv6-connectivity/. On Mac or Linux systems, the default gateway can be checked 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 10.248.221.30 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 fe80:7278:c004:f167:c5ca%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): {159.213.165.220, 8.198.16.108}
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 6b:d6:d6:8c:2d:ec
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 3c:6a:39:2f:37:45
}
Solutions for Resolving Connectivity Issues
When it comes to transferring data to your router, you might be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Handy Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are running, such as 10.13.1, 11.4.1, or 12.2.2, there exists a variety of troubleshooting tools. However, these manual actions and scripts fail to provide a set of interconnected values over a period of time. This is where the automated remote troubleshooting approach becomes extremely useful, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Pre-Installed Scripts for Assistance
An incredibly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to produce a wide range of logs, although much of it is only relevant to wireless at a specific moment, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (despite minimal interaction), you can enter sudo /usr/bin/sysdiagnose and it will display a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can manually navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. Just be cautious of the file sizes, which are approximately 300MB.
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