How To Support OSX Internet
Understanding Internet Addressing
When using the Internet, individuals are assigned either a Public IPv4 address (e.g. 201.51.82.200) or an IPv6 address (e.g. 2000:4c6a:9352:b9af:8f92:ea92:5f7f:146d). These addresses can be verified at https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses, or even referencing MAC addresses (e.g. cf:6c:8f:3c:db:8b) can be prone to errors and quickly become complex. Additionally, these addresses do not provide any historical data, especially regarding past issues.
Navigating the World Wide Web
When attempting to access a website such as https://mclaughlin.co, the first step involves contacting a DNS server to translate the host portion (mclaughlin) in combination with the Top Level Domain (co) of the URL into an IP address (e.g. 35.5.27.166). Most web requests from your computer and browser include details such as: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Typically, your default gateway is automatically configured via DHCP and results in an address such as 172.24.24.6 (usually ending in .1 or .254 based on the scope size). This is where all of your computer’s traffic is directed for further routing. For IPv6, there is a detailed explanation available at how-to-fix-ipv6-connectivity/, and you can verify this 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 172.24.24.6 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 fe80:2bda:37d5:e0e6:5a%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): {90.39.237.52, 254.27.92.94}
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 cf:6c:8f:3c:db:8b
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 fd:8f:9c:38:6a:ab
}
Resolve Issues with Wired or Wireless Connections
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.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.2, 11.5.4, or 12.1.4, there are various tools available for resolving issues. However, these manual actions and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for remote teams and those following a Work From Anywhere (WFA) practice.
Useful Built-in Scripts
One highly beneficial tool on OSX/macOS is sudo wdutil info, which provides a detailed dump of the current wireless related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive range of logs (although much of it is specific to wireless and is only point-in-time, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there is minimal interaction), you can execute sudo /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 using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.
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