How Can I DiagnOSe Apple Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 166.170.213.157, or an IPv6 address, like 2000:e89d:f16f:7afc:1780:bdfc:b553:a2c6. The website https://test-ipv6.com/ allows for easy verification of these addresses. However, sharing and communicating these addresses, as well as MAC addresses like 91:5c:dc:34:00:50, can be prone to errors and quickly become complex. Furthermore, it does not provide historical data, especially related to previous issues.
Navigating the World Wide Web
To access a website, such as https://kulas.info, your computer initially communicates with a DNS server in order to translate the host portion (kulas) combined with the Top Level Domain (info) of the URL into an IP address, such as 2.77.145.65. Additionally, your computer and browser specify their type with every web request, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway, typically obtained via DHCP, is an automatically configured address, such as 192.168.35.131 (usually ending in .1 or .254 based on the scope size). This location is where your computer sends all of its traffic to be routed onwards. For IPv6, a detailed explanation can be found at how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be verified 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 192.168.35.131 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:e095:32b:8414:ae41%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): {192.188.39.152, 97.134.108.177}
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 91:5c:dc:34:00:50
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 00:56:50:8d:48:b5
}
Resolve Issues with Wireless and Wired Connections
When it comes to transmitting data to your router, you have the option of using a wired or wireless (Wi-Fi) medium at the physical and data layer.
How to Address Problems on Apple macOS / OSX
Regardless of whether you’re running OSX/macOS versions 10.14.1, 11.4.6, or 12.1.8, there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilize Pre-Installed Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although many are only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will produce logs in /var/tmp/<blah>.tar.gz. For an interactive run, you can executesudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the path. Be mindful of the file size, which is approximately 300MB.
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