Understand MacOS Internet Connection
Understanding the Functioning of Internet Addressing
When using the Internet, individuals may receive a Public IPv4 address such as 218.152.32.2 or an IPv6 address like 2000:3a1f:56b9:90f1:6219:ee0d:cb74:7d18. It is possible to verify this by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying these addresses and even specifying MAC addresses like 96:48:2e:03:96:c8 can lead to errors and complications. It is important to note that this method does not provide historical data, particularly from past incidents.
Navigating the Internet
In order to access a website, such as https://schuppe.biz, you must first reach a DNS server to convert the host portion (schuppe) combined with the Top Level Domain (biz) of the URL into an IP address. For instance, 252.48.255.183. Upon making web requests, your computer and browser also convey their type, as seen in the example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
The default gateway assigned via DHCP is typically an automatically configured address. It is common to receive a default gateway like 10.137.66.111 (usually ending in .1 or .254 depending on the scope size), which serves as the point where your computer directs all its traffic for routing. For IPv6, detailed instructions can be found in the deep dive on how-to-fix-ipv6-connectivity/, and check the settings on Mac or Linux.
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 10.137.66.111 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 fe80:60c8:35b1:d5ef:fa8b%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): {130.137.226.249, 166.176.33.254}
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 96:48:2e:03:96:c8
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 d9:19:d0:64:52:da
}
Resolve Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX
Regardless of whether you are running OSX/macOS version 10.14.4, 11.4.5, or 12.3.6, there are various tools available for resolving issues. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that have adopted remote work and the Work From Anywhere (WFA) approach.
Utilizing Built-in Scripts
One particularly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although many of the logs are only relevant to the current wireless settings, similar to what wdutil provides.
By running the command sudo nohup /usr/bin/sysdiagnose -u & in the background, the logs will be written to /var/tmp/<blah>.tar.gz. For an interactive mode (although not much interaction is required), you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it will open Finder in the correct location, or otherwise you can navigate to /var/tmp using Finder with Cmd+Shift+G. It’s important to note that the file sizes are approximately 300MB.
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