How Do You Check MacOS No-access
Understanding IP Addressing
When connecting to the Internet, you are assigned a unique public IPv4 address such as 157.19.193.99 or an IPv6 address like 2000:6a6d:9375:b611:7480:ae17:32f:dc0f. These addresses can be verified on https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying these addresses, and even MAC addresses like d5:da:53:b3:b1:2f, can be prone to errors and quickly become complicated. Moreover, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
Accessing a website such as https://zulauf.io involves initially accessing a DNS server to convert the host segment (zulauf) along with the Top Level Domain (io) of the URL into an IP address like 160.147.250.44. When making web requests, your computer and browser also include type information such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0.
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. Your computer receives a default gateway like 10.89.37.226 (usually ending in .1 or .254 based on the scope size), which is responsible for routing all traffic from your computer. For IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available. Additionally, on Mac or Linux, you can verify this with:
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 10.89.37.226 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:bb9f:db92:c1df:83e0%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): {110.238.107.142, 155.39.134.75}
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 d5:da:53:b3:b1:2f
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:be:7a:df:30:3f
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you could be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Guide for Apple macOS / OSX
Irrespective of your version of OSX/macOS - whether it’s 10.11.5, 11.3.6, or 12.0.6 - there are several 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 essential, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Utilizing Built-in Scripts for Assistance
A very useful tool on OSX/macOS is the sudo wdutil info command, which dumps current wireless-related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be utilized to generate a wide range of logs, although many are only relevant to wireless settings, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose. However, be mindful of the file sizes, which are typically around 300MB.
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