How To Check Mac Connectivity
Understanding How Internet Addressing Functions
When accessing the Internet, individuals may be assigned a Public IPv4 address such as 129.124.114.215 or an IPv6 address like 2000:c47:1987:d679:4acd:b028:77a8:c808. This information can be verified by visiting https://test-ipv6.com/. However, explaining and communicating these complex addresses, or even referencing MAC addresses like 1f:1d:a7:2f:58:7c, can quickly become complicated and error-prone, especially for those who are not tech-savvy. Additionally, it does not provide any historical data, particularly when previous issues arose.
Navigating the World Wide Web
When attempting to access a website such as https://heaney-lueilwitz.com, the first step is to contact a DNS server to convert the host portion (heaney-lueilwitz) along with the Top Level Domain (com) of the URL into an IP address, for example, 199.186.16.112. Furthermore, every web request sent by your computer and browser includes its type, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0.
The Significance of Default Gateways
Typically, your default gateway is automatically assigned by DHCP and appears as an address like 172.31.75.212 (commonly ending in .1 or .254 depending on the scope size). This gateway is where your computer sends all of its traffic to be routed onward. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available, and on Mac or Linux, one can verify this by executing:
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 172.31.75.212 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 fe80:3dfd:40ef:ddf4:7b9f%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): {48.224.14.219, 240.193.107.191}
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 1f:1d:a7:2f:58:7c
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 39:9b:b6:ff:2d:62
}
Resolving Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps to Take for Apple macOS / OSX Users
Regardless of the version of OSX or macOS you are using, whether it’s 10.12.5, 11.0.8, or 12.2.7, there are a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One of the most helpful tools on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI. This command can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time information related to wireless, similar to wdutil.
To run the sysdiagnose tool in the background and write the logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, which will generate 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. Keep in mind that the file sizes are approximately 300MB.
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