DiagnOSe OSX Connectivity

The Process of Internet Addressing

When using the Internet, you are assigned a Public IPv4 address such as 203.53.142.39 or an IPv6 address like 2000:179a:49:856d:4a8e:73e1:9480:b978. You can verify this at https://test-ipv6.com/. However, communicating these addresses as well as MAC addresses like 21:b5:a2:e3:a6:db can be prone to errors, especially for non-technical individuals. Moreover, historical data about previous problems is not provided.

Navigating the Internet

Accessing a web page such as https://stokes.name involves the initial step of reaching out to a DNS server to convert the host portion (stokes) combined with the Top Level Domain (name) of the URL into an IP address like 59.110.140.130. Your computer and browser transmits the type with all web requests e.g.
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16

The Significance of Default Gateways

The default gateway is typically an automatically assigned address via DHCP. Usually, you receive a default gateway like 192.168.42.119 (although they generally end in .1 or .254 depending on the scope size), which is the focal point where your computer forwards all of its traffic. For IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/, or you can verify it on Mac or Linux using:

### 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  192.168.42.119    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:f583:2917:276e:b5cd%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): {148.194.177.197, 141.142.157.167}
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 21:b5:a2:e3:a6:db
  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 da:0c:e1:99:37:04
}

Resolving Connectivity Issues for Wired and Wireless Networks

When it comes to sending data to your router, there are different troubleshooting methods for both wired and wireless (Wi-Fi) connections at the physical and data layer.

Tips for Apple macOS / OSX Users

Regardless of whether you are using OSX or macOS, whether it’s version 10.15.7, 11.6.9, or 12.1.3, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that operate remotely and embrace the Work From Anywhere (WFA) concept.

Utilizing In-Built Scripts for Assistance

One useful tool for OSX/macOS users is the 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 wide range of logs, although many of them are only relevant to wireless settings, similar to wdutil.

To run the sysdiagnose tool in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, if you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will provide a privacy warning. The generated logs can be found in the correct location within Finder or by navigating to /var/tmp or using Finder with Cmd+Shift+G to point Finder to the path. It’s important to be aware of the file sizes, which are typically around 300MB.

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Table 1.0 - Video Help