How Do You Understand Mac Connectivity
Understanding the Functionality of Internet Addressing
When using the Internet, one might have a Public IPv4 address such as 236.164.83.253 or an IPv6 address like 2000:3c88:5614:9bdc:afe7:13ee:ce00:f0. This can be verified at https://test-ipv6.com/. However, communicating these addresses to those who are not technologically inclined can be prone to errors and can become complex, especially when dealing with MAC addresses like c0:a4:f9:9e:a0:03. Additionally, this does not provide historical data, which can be important when troubleshooting past issues.
Navigating the World Wide Web
To access a web page such as https://harber.biz, you first contact a DNS server to translate the host portion (harber) and the Top Level Domain (biz) of the URL into an IP address, such as 174.13.147.93. When making web requests, your computer and browser typically include its type, for example:
<br>```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 an address that is automatically configured via DHCP. This address, such as 192.0.0.10 (although it typically ends in .1 or .254, depending on the scope size), is where your computer sends all of its traffic to be routed onwards. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be checked with:
<br>
```bash
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 192.0.0.10 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 fe80:7b37:5c37:6444:8289%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): {135.53.179.60, 92.94.248.140}
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 c0:a4:f9:9e:a0:03
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 e7:87:c3:47:8d:d0
}
Diagnosing Connectivity Issues for Wired and Wireless Networks
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.
Strategies for Addressing Problems on Apple macOS / OSX
Regardless of whether you are running OSX or macOS, such as 10.14.4, 11.0.8, or 12.3.5, there are various methods for troubleshooting connectivity issues. However, these manual methods and scripts do not provide a continuous stream of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that are embracing remote work and the concept of Work From Anywhere (WFA).
Leveraging Pre-Installed Tools for Assistance
One particularly useful tool on OSX/macOS is sudo wdutil info, which provides a detailed dump of the current wireless settings to the CLI, and it can be set up to generate specific logs for troubleshooting purposes. Another, more comprehensive tool is sysdiagnose, which can generate a wide array of logs, although much of it pertains to wireless settings and is mostly point-in-time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute sysdiagnose in the background and create logs at /var/tmp/<blah>.tar.gz for further analysis. For an interactive experience (although there is minimal interaction), you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes are typically around 300MB.
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