How Can I Fix Mac No-access
An Overview of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 27.193.35.190, or an IPv6 address, like 2000:6df1:d8d5:7ae5:a446:602d:27e6:cee5. You can verify this information by visiting https://test-ipv6.com/. However, relaying these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses like 12:7e:1c:37:bf:5c, can lead to errors and complexity. Moreover, this method does not provide historical data, especially when previous issues occurred.
Navigating the Internet
When attempting to access a website, such as https://leannon.com, you initially connect to a DNS server to convert the host portion (leannon) combined with the Top Level Domain (com) of the URL, to an IP address like 117.229.250.218. Your computer and browser transmit its type with all web requests, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
The default gateway is typically assigned automatically through DHCP. You receive a default gateway, such as 192.0.0.4 (although they typically end in .1 or .254 depending on the size of the network), and this is the point to which your computer forwards all its traffic. For IPv6, detailed instructions are available in the article how-to-fix-ipv6-connectivity/, but for Mac or Linux, you can check using the following command:
```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 192.0.0.4 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:c734:1530:a5f2:a0e4%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): {130.219.99.38, 159.145.215.192}
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 12:7e:1c:37:bf:5c
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 2f:d6:36:86:2f:6e
}
Solutions for Wired and Wireless Connectivity Issues
When it comes to sending data to your router, you could be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Connectivity Problems on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.12.6, 11.4.9, or 12.1.7, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for remote work and Work From Anywhere (WFA) teams.
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings via CLI and can also be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to generate a wide range of logs, although most are only relevant to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be aware of the large file sizes, around 300MB or more.
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