How Can I Fix MacOS Connectivity

The Functioning of Internet Addressing

When using the Internet, individuals may receive a Public IPv4 address like 147.53.239.119 or an IPv6 address like 2000:c13b:2236:8129:4e8f:406b:86e8:d6a0. This information can be verified at https://test-ipv6.com/. However, conveying these addresses to non-technical people, or even mentioning MAC addresses like 68:35:52:20:d7:30, can be susceptible to errors and becomes complex rapidly. Additionally, this does not provide any historical data, particularly when past issues occurred.

Navigating the Internet

When attempting to access a website like https://cassin-veum.io, the first step is to contact a DNS server to convert the host portion (cassin-veum) combined with the Top Level Domain (io) of the URL to an IP address like 153.177.59.169. Your computer and browser include its type with all web requests, 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, the default gateway is an automatically configured address via DHCP. A default gateway like 172.21.56.121 (usually ending in .1 or .254, depending on the scope size) is where your computer sends all its traffic to be routed onwards. For IPv6, there is a detailed explanation available at how-to-fix-ipv6-connectivity/. On Mac or Linux, this can be verified by using:

### IPv4 Routes and the Host IPv4 Route Table (inc. VPN)
```netstat -rn -f inet | egrep -i "default|0/1|128.0/1"```

<pre>
0/1      172.18.12.193  UGScg  utun3
default  172.21.56.121    UGScg  en0
128.0/1  172.18.12.193  UGSc   utun3</pre>

**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. 

<pre>
default   fe80:bfa:d7ea:b6eb:203f%en0  UGcg   en0
default   fe80::%utun0                   UGcIg  utun0
default   fe80::%utun1                   UGcIg  utun1
default   fe80::%utun2                   UGcIg  utun2
2000::/3  utun3                          USc    utun3</pre>

**Note:** We are not just looking for the default but also for any VPN that overrides the public v6 address space.
<br>

## Debugging DHCP for both IPv4 and IPv6

To get a look at the low level DHCP configuration (Mac/Linux): 

```ipconfig getpacket en0```

<pre>
...
domain_name_server (ip_mult): {138.26.243.42, 233.107.231.29}
end (none):
...</pre>

So, in the above we are not getting IPv6 DNS servers from the DHCPv4 reply but...

```ipconfig getv6packet en0```

<pre>
DHCPv6 REPLY (7) Transaction ID 0x80940b Length 76
Options[4] = {
  CLIENTID (1) Length 14: DUID LLT HW 1 Time 668691856 Addr 68:35:52:20:d7:30
  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 74:cb:7a:b6:08:2e
}</pre>




## Fixing Connectivity Issues for Wired or Wireless Networks

When it comes to sending data to your router, you might be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
### Troubleshooting Solutions for Apple macOS / OSX Users
Regardless of whether you are using OSX or macOS versions like ```10.15.9```, ```11.5.5```, or ```12.0.7```, there are various troubleshooting tools available. However, these manual actions and scripts fail to provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that are embracing remote work and the concept of Work From Anywhere (WFA).
#### Useful Built-in Scripts for macOS Users
An extremely useful tool for OSX/macOS users is the ```sudo wdutil info```, which provides a dump of the current wireless settings to the CLI. This tool can also be configured to generate specific logs for troubleshooting purposes. Additionally, the ```sysdiagnose``` tool offers a more comprehensive option for generating a wide range of logs, although many of them are only point-in-time related to wireless, similar to wdutil.

To run the ```sysdiagnose``` tool in the background and generate logs in the ```/var/tmp/<blah>.tar.gz``` location, use the command ```sudo nohup /usr/bin/sysdiagnose -u &```. Alternatively, for interactive use, run ```sudo /usr/bin/sysdiagnose```, but be mindful of the file sizes, which can be around 300MB. After running the command, the logs will be located in the ```/var/tmp``` directory.
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|Video | Title | Channel |
| :---: | :---: | :---: |
|<a href="https://www.youtube.com/watch?v=VwNYWAxHCgM" data-lity><img src="https://i.ytimg.com/vi/VwNYWAxHCgM/default.jpg" class="img-fluid"></a>|<a href="https://www.youtube.com/watch?v=VwNYWAxHCgM" data-lity>Secret Mac Boot Commands - Mac Boot Key Combinations</a>|<a target="_blank" href="https://www.youtube.com/channel/UCg43DP8MdHVcl4rFK_delBg" >Hands-On Mac</a>|
|<a href="https://www.youtube.com/watch?v=JMKi6o9kaZI" data-lity><img src="https://i.ytimg.com/vi/JMKi6o9kaZI/default.jpg" class="img-fluid"></a>|<a href="https://www.youtube.com/watch?v=JMKi6o9kaZI" data-lity>macOS Big Sur - What&#39;s New in Apple macOS 11</a>|<a target="_blank" href="https://www.youtube.com/channel/UCg43DP8MdHVcl4rFK_delBg" >Hands-On Mac</a>|
|<a href="https://www.youtube.com/watch?v=7KdhJimuhNw" data-lity><img src="https://i.ytimg.com/vi/7KdhJimuhNw/default.jpg" class="img-fluid"></a>|<a href="https://www.youtube.com/watch?v=7KdhJimuhNw" data-lity>Securing macOS Big Sur</a>|<a target="_blank" href="https://www.youtube.com/channel/UCg43DP8MdHVcl4rFK_delBg" >Hands-On Mac</a>|
|<a href="https://www.youtube.com/watch?v=TWzWd_DiaJ0" data-lity><img src="https://i.ytimg.com/vi/TWzWd_DiaJ0/default.jpg" class="img-fluid"></a>|<a href="https://www.youtube.com/watch?v=TWzWd_DiaJ0" data-lity>Mac Activity Monitor - How to Troubleshoot Your Mac</a>|<a target="_blank" href="https://www.youtube.com/channel/UCg43DP8MdHVcl4rFK_delBg" >Hands-On Mac</a>|
|<a href="https://www.youtube.com/watch?v=HEbK-Tignuc" data-lity><img src="https://i.ytimg.com/vi/HEbK-Tignuc/default.jpg" class="img-fluid"></a>|<a href="https://www.youtube.com/watch?v=HEbK-Tignuc" data-lity>On the Road to Big Sur 2 - Compatibility</a>|<a target="_blank" href="https://www.youtube.com/channel/UCg43DP8MdHVcl4rFK_delBg" >Hands-On Mac</a>|

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