How To DiagnOSe Apple Internet Connection
Explanation of Internet Addressing
When using the Internet, a unique Public IPv4 address such as 150.118.236.83 or an IPv6 address like 2000:8a28:b44:23df:2f83:d768:aafc:ff3e is assigned. This information can be verified at https://test-ipv6.com/, although communicating or referencing these addresses (or MAC addresses like d2:93:65:a7:6c:9e) can be tricky for those without technical expertise, especially when historical data is needed.
How Web Pages are Accessed
To access a specific web page, such as https://veum.co, the initial step involves consulting a DNS server to convert the URL’s host portion (veum) combined with its Top Level Domain (co) into an IP address like 46.56.179.29. Additionally, all web requests sent by your computer and browser contain information about the type of device, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
By default, the gateway address is automatically configured through DHCP and typically takes the form of 192.168.112.4 (although it usually ends in .1 or .254 based on the scope size). This is the location where your computer forwards all its traffic for routing. For those interested in more information about IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/. On Mac or Linux platforms, this can be verified by using specific commands.
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 192.168.112.4 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 fe80:42db:7412:89dc:b3f6%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): {114.162.225.101, 255.183.205.94}
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 d2:93:65:a7:6c:9e
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 67:6e:5f:4c:ee:36
}
Resolving Connectivity Issues in Wired and Wireless Networks
When it comes to sending data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Whether you are running OSX/macOS version 10.13.4, 11.2.6, or 12.3.4, there are a variety of tools available for troubleshooting. Unfortunately, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that operate remotely and embrace Work From Anywhere (WFA) practices.
Helpful Built-in Scripts
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time only in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, use sudo /usr/bin/sysdiagnose, which 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. Keep in mind that the file sizes are around 300MB or so.
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