How Do You Understand OSX Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 110.254.190.237 or 2000:4db9:302:e972:d20d:b978:c35f:36db. You can verify this through https://test-ipv6.com/. However, explaining these addresses to individuals who are not technologically savvy can be prone to errors and quickly become complex. Furthermore, this method does not provide any historical data, especially during past issues.
Navigating the World Wide Web
In order to access a website like https://kutch.net, your computer first contacts a DNS server to translate the host (kutch) and the Top Level Domain (net) of the URL into an IP address, such as 98.253.253.154. Additionally, your computer and browser communicates its specifications with each web request, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
The default gateway is typically an address that is configured automatically via DHCP. This default gateway, such as 172.31.53.235 (often ending in .1 or .254 depending on the scope size), is where your computer directs all of its traffic to be routed onwards. For IPv6, you can refer to our in-depth guide on how-to-fix-ipv6-connectivity/ or check on Mac or Linux using the following command:
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 172.31.53.235 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 fe80:77d4:e045:f187:c704%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): {84.147.234.32, 107.1.85.41}
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 47:20:f1:d6:76:2a
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 a9:2f:e0:4a:f2:61
}
Resolve Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.11.4, 11.0.4, or 12.3.8, there are various tools available for resolving issues. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that adopt remote work and Work From Anywhere (WFA) policies.
Utilizing Built-in Scripts to Aid Troubleshooting
An extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless related settings to the CLI, and can be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time information in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (despite the minimal interaction), you can use the command sudo /usr/bin/sysdiagnose, but be prepared for file sizes of around 300MB.
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