How To Check OSX Connectivity
Understanding the Operation of Internet Addresses
When using the Internet, you will be assigned a Public IPv4 address and an IPv6 address. These addresses can be checked using https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses, to non-technical individuals can be challenging and error-prone. Furthermore, it lacks historical data, especially regarding past issues.
Navigating the World Wide Web
Accessing a website such as https://wisozk.co involves reaching out to a DNS server to convert the host portion and the Top Level Domain of the URL to an IP address. Additionally, every web request from your computer and browser includes its type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
The default gateway, generally obtained via DHCP, is an automatically configured address for routing all computer traffic. Although default gateways usually end in .1 or .254, depending on the scope size, we have a detailed discussion on how-to-fix-ipv6-connectivity/ for IPv6. Mac and Linux users can also check this.
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 172.27.145.194 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 fe80:72c7:53e2:88d9:6051%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): {212.79.34.245, 93.177.66.162}
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 67:4c:20:d8:21:3d
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 e8:ad:b1:a6:4f:9d
}
Troubleshooting Connectivity Issues in Wired and Wireless Networks
When transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Connectivity Problems on Apple macOS / OSX Systems
Regardless of whether you are running versions such as OSX, 10.12.2, 11.5.6, or 12.1.4, there are various troubleshooting tools available. However, the manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that encourage remote work and Work From Anywhere (WFA).
Using Built-in Scripts for Assistance
On OSX/macOS, the sudo wdutil info command is quite useful as it provides a dump to the CLI of current wireless settings and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a variety of logs related to wireless, although much of it is only valid at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command: sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose and follow the prompts. However, be mindful of the file sizes, which can be around 300MB or more.
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