How To Fix Mac No-access

Understanding Internet Protocol Addressing

The way the Internet assigns addresses may result in receiving a Public IPv4 address such as 134.97.29.128 or an IPv6 address like 2000:ebef:bcc:fb17:4a1f:b7f3:1449:afd5. Validation of this can be done through https://test-ipv6.com/, however, for those without technical expertise, communicating these addresses or MAC addresses like 68:54:bb:0c:37:95 can be prone to errors and quickly become complex. Furthermore, it does not provide historical data.

Navigating the World Wide Web

To access a website such as https://lakin.info, you initially contact a DNS server to convert the host portion (lakin) along with the Top Level Domain (info) of the URL into an IP address, such as 157.83.154.100. In all web requests, your computer and browser send its type, for example:
Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285

The Significance of Default Gateways

Usually, your default gateway is an address configured automatically via DHCP. It usually ends in .1 or .254, depending on the scope size, such as 192.168.140.191. This is where your computer sends all its traffic to be routed onwards. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available, but you can verify on Mac or Linux using:

command

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  192.168.140.191    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:bcd3:2f02:9a19:f2da%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): {53.62.69.208, 73.228.6.63}
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 68:54:bb:0c:37:95
  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 78:c9:6a:78:e6:7e
}

Fixing Network Connectivity Issues

When it comes to sending data to your router at the physical and data layer, you may encounter connectivity issues with wired or wireless (Wi-Fi) mediums.

How to Troubleshoot Network Problems on Apple Devices

Regardless of which version of OSX/macOS you are using - whether it’s 10.11.6, 11.4.3, or 12.1.9 - there are various troubleshooting tools available. However, the manual actions and scripts may not provide a comprehensive set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are transitioning towards remote work and adopting a Work From Anywhere (WFA) approach.

Utilizing Built-in Scripts for Assistance

One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a command-line dump of current wireless settings and can be configured to generate specific troubleshooting logs. Moreover, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although much of it is only relevant to wireless networks, similar to wdutil.

To run the sysdiagnose tool in the background and generate logs at /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer running it interactively, you can utilize sudo /usr/bin/sysdiagnose with the necessary privacy warnings. Keep in mind that the file sizes can be around 300MB or slightly more.

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