How Can I DiagnOSe OSX No-access

Demystifying Internet Addressing

When using the Internet, you are assigned a Public IPv4 address, such as 207.122.154.133, or an IPv6 address, like 2000:8221:40b9:ef0a:12fa:3a79:b120:f784. To verify this, you can visit https://test-ipv6.com/. However, for individuals with limited technical knowledge, conveying these addresses or MAC addresses like 7c:79:6c:05:45:ce can be prone to errors and quickly become complicated. Furthermore, this method lacks historical data, especially when attempting to resolve past issues.

Navigating the World Wide Web

To access a website such as https://senger-hane.co, you must initially connect to a DNS server to translate the host portion (senger-hane), combined with the Top Level Domain (co) of the URL, to an IP address like 186.19.142.65. When making web requests, your computer and browser include its type, as demonstrated below:

Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)

Understanding the Significance of Default Gateways

Typically, your default gateway is an automatically configured address obtained via DHCP, such as 10.99.50.210 (although they usually end in .1 or .254, depending on the scope size). This is where your computer sends all of its traffic to be routed onwards. For IPv6, we provide a detailed guide on how-to-fix-ipv6-connectivity/, or you can check on Mac or Linux using the following syntax:

<br>

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  10.99.50.210    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   fe80:5077:26eb:ed53:95b2%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): {120.75.24.174, 159.142.196.71}
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 7c:79:6c:05:45:ce
  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 12:72:d7:82:c0:2b
}

Resolving Issues with Wired and Wireless Connectivity

In the realm of physical and data layer connectivity, the utilization of wired or wireless (Wi-Fi) mediums to transmit data to your router is common.

Actions to Take for Apple macOS / OSX Users

Irrespective of whether you are using OSX/macOS version 10.15.6, 11.5.2, or 12.3.1, there exists a variety of troubleshooting tools. However, the limitation of these tools is that they do not provide a set of correlated values over a period of time. For this reason, remote troubleshooting has become especially valuable, particularly for teams endorsing remote work and Work From Anywhere (WFA) culture.

Utilizing Pre-Installed Scripts for Assistance

One particularly beneficial tool available on OSX/macOS is the sudo wdutil info command, which provides a detailed report to the CLI of the current wireless settings, and can also be set up to create specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool can be used to generate a wide range of logs, although it mainly provides point-in-time data in relation to wireless, similar to wdutil.

To run the sysdiagnose tool in the background and produce logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (although there is limited interaction), execute the command sudo /usr/bin/sysdiagnose, which will display a privacy warning. When run in this way, it should open Finder in the relevant location, or you can manually navigate to /var/tmp or use Finder with Cmd+Shift+G to direct Finder to the path. Be mindful of the file sizes, which can be around 300MB.

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