How Can I Test MacOS Connectivity
Explanation of Internet Addressing
When using the Internet, individuals are assigned a Public IPv4 address, such as 61.71.85.86, or an IPv6 address, like 2000:b70c:b62c:9742:2cc8:1cd0:7b81:87a0. To verify their address, they can visit https://test-ipv6.com/. However, for those not well-versed in technology, communicating these addresses or MAC addresses, such as 9f:9b:35:5b:2e:13, can lead to errors and complexity. Moreover, this method lacks historical data, especially regarding previous issues.
Web Page Access
Upon attempting to access a webpage, such as https://kulas.org, individuals first consult a DNS server to translate the URL’s host (kulas) and Top Level Domain (org) into an IP address, such as 112.242.74.149. Additionally, every web request includes the user’s computer and browser type, for instance: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
The default gateway is usually automatically configured through DHCP and is assigned a default gateway, like 192.168.102.89 (typically ending in .1 or .254, depending on the scope size). This is where a computer forwards all its traffic to be routed onwards. For IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available, and for Mac or Linux users, the address can be checked with:
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 192.168.102.89 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:fc90:4561:d397:8fa5%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): {82.11.7.3, 234.126.193.53}
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 9f:9b:35:5b:2e:13
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 e3:a4:13:79:74:5c
}
Fixing Connection Issues in Wired or Wireless Networks
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you’re running 10.15.2, 11.2.1, or 12.1.6, there are several troubleshooting tools for OSX/macOS. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams embracing remote work and Work From Anywhere (WFA) practices.
Useful Built-in Scripts
One of the helpful tools 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 troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a variety of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively using sudo /usr/bin/sysdiagnose, which will give a privacy warning. When run interactively, it should open Finder in the correct location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB.
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