How Do You Check MacOS Issues
The Functioning of Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address, such as 137.46.211.62, or an IPv6 address like 2000:20c7:2a87:1ca8:4e14:30c8:815f:b8a4. You can verify this by visiting https://test-ipv6.com/. However, attempting to relay these addresses to individuals who are not well-versed in technology, or even mentioning MAC addresses like 2e:8b:d7:47:5c:51, can be prone to error and quickly become complex. Moreover, this does not provide any historical data, especially from previous incidents.
Navigating the Internet
In order to access a web page such as https://blick.net, you first connect to a DNS server to translate the host portion (blick) combined with the Top Level Domain (net) of the URL into an IP address, for example, 233.152.95.64. Whenever initiating web requests, your computer and browser both share their types, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Typically, your default gateway is an automatically allocated address through DHCP, like 172.27.131.211 (usually ending in .1 or .254 based on the scope size). This is the location where your computer directs all of its traffic to proceed further. For IPv6, we have an extensive breakdown available at how-to-fix-ipv6-connectivity/, and you can check 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 172.27.131.211 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 fe80:27f9:301b:7de4:4e9c%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): {29.64.208.167, 111.36.211.11}
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 2e:8b:d7:47:5c:51
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 d2:19:0e:da:be:da
}
Resolve Connectivity Issues with Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Recommendations for Apple macOS / OSX Users
Regardless of whether you are on OSX or macOS, whether it’s version 10.11.8, 11.6.2, or 12.0.9, there are various troubleshooting tools available. However, these tools only provide isolated data and lack the ability to track correlated values over time. This is where automated remote troubleshooting proves to be valuable, especially for teams that have fully embraced remote work and the concept of Work From Anywhere (WFA).
Leveraging Built-in Scripts for Assistance
On OSX/macOS, the sudo wdutil info command is a useful tool that provides a dump of current wireless settings via the CLI, and it can also be configured to generate specific logs for troubleshooting purposes. In addition, the sysdiagnose tool offers a more comprehensive solution by producing a wide range of logs, although many of these are only relevant to the wireless network at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs at /var/tmp/<blah>.tar.gz, the command sudo nohup /usr/bin/sysdiagnose -u & can be used. For an interactive experience that includes a privacy warning, the command sudo /usr/bin/sysdiagnose can be executed. When not run in the background, this command should open Finder in the appropriate location, allowing you to access the logs at /var/tmp or by using Finder with Cmd+Shift+G to navigate to the specified path. It’s important to note that the file sizes range from approximately 300MB or slightly more.
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