DiagnOSe Mac Issues
Understanding Internet Addressing
When it comes to the Internet, you may have a designated Public IPv4 address, such as 213.61.72.50, or an IPv6 address, like 2000:6de9:7d90:9409:500a:bb0f:e2f3:da92. To verify this, you can visit https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses like 41:7b:5c:d0:b9:74, can quickly become error-prone and complicated. Moreover, this method does not provide any historical data, particularly from past occurrences of problems.
Navigating the Web
In order to access a website like https://buckridge.io, you first need to reach a DNS server to convert the host portion (buckridge) combined with the Top Level Domain (io) of the URL into an IP address, such as 76.113.93.157. Additionally, your computer and browser include its type in all web requests, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
Your default gateway is typically an automatically configured address via DHCP. It usually looks like 172.22.134.109 (although they often end in .1 or .254 depending on the scope size), and it is the point where your computer sends all its traffic to be routed onwards. For IPv6, there is a comprehensive guide available at how-to-fix-ipv6-connectivity/, but you can check 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 172.22.134.109 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 fe80:30e2:32c8:3921:54d7%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): {156.93.46.123, 68.118.62.62}
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 41:7b:5c:d0:b9:74
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 e6:66:de:a3:d8:cc
}
Diagnosing and Resolving Connectivity Issues
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Strategies for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.15.7, 11.4.7, or 12.1.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves beneficial, particularly for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Utilizing Built-in Tools for Assistance
On OSX/macOS, the sudo wdutil info tool is quite useful as it provides a dump of current wireless related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool offers a comprehensive solution for generating a wide range of logs, although many of them are point in time only in relation to wireless, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz, or to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will prompt 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 utilize Finder with Cmd+Shift+G to point Finder to the path. It’s important to be mindful of file sizes, which are approximately 300MB.
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