How To Support OSX Internet Connection
Working Mechanism of Internet Addressing
When accessing the Internet, you are assigned a Public IPv4 address such as 51.124.212.17 or an IPv6 address like 2000:b260:4fed:a1b5:415b:4f1d:23a8:7f72. You can verify this information using https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses or even mentioning MAC addresses like 10:af:d1:b3:c7:cb can be error-prone and quickly become complex. Furthermore, this approach does not provide any historical data, particularly regarding past issues.
Inquiring the World Wide Web
To access a website such as https://fahey.name, you first contact a DNS server to convert the host part (fahey) combined with the Top Level Domain (name) of the URL into an IP address like 136.84.137.18. Your computer and browser disclose their type 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.
Significance of Default Gateways
Typically, your default gateway is an automatically configured address through DHCP. You receive a default gateway like 172.20.203.177 (usually ending in .1 or .254 based on the scope size), which serves as the destination for all your computer’s outgoing traffic to be routed. For IPv6, you can find detailed guidance on how-to-fix-ipv6-connectivity/, and this can be verified on Mac or Linux by:
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 172.20.203.177 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:c645:6f34:b082:dc17%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): {173.205.51.146, 150.193.49.191}
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 10:af:d1:b3:c7:cb
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 83:04:ea:c8:54:46
}
Troubleshooting Connectivity Issues in Wired and Wireless Networks
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips and Tricks for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re using - whether it’s 10.14.2, 11.5.3, or 12.1.7 - there are a variety of troubleshooting tools available. However, the manual actions and scripts available do not provide a series of correlated values over time. This is where automated remote troubleshooting can be particularly useful, especially for teams that have embraced remote work and the Work From Anywhere (WFA) concept.
Using Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose, but be aware that it will give a privacy warning. When 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. Be cautious of the file sizes, as they can be around 300MB.
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