How To DiagnOSe Apple IP Settings
Understanding Internet Addressing
When connecting to the internet, you are assigned a Public IPv4 address (e.g. 234.151.179.41) or an IPv6 address (e.g. 2000:7e23:17e1:81c8:271:10d:77c6:8f6e). You can verify this information at https://test-ipv6.com/. However, conveying these addresses to individuals who are not technically inclined or mentioning MAC addresses like f6:49:ea:39:7f:64 can be prone to errors and become complex quickly. Moreover, this approach lacks historical data, especially when addressing past issues.
Navigating the World Wide Web
Accessing a web page such as https://larkin.io begins with contacting a DNS server to convert the host segment (larkin) combined with the Top Level Domain (io) of the URL to an IP address, such as 113.209.123.106. Your computer and browser transmit their information with every web request (e.g. Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0).
The Significance of Default Gateways
The default gateway, typically an automatically configured address via DHCP, is the point to which your computer directs all of its traffic to be routed onwards. You receive a default gateway such as 192.0.0.95 (although they commonly end in .1 or .254 based on the scope size). For a more in-depth look at IPv6, you can refer to how-to-fix-ipv6-connectivity/. To check on Mac or Linux, you can use:
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 192.0.0.95 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 fe80:9537:d2cc:db1f:7577%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): {130.231.97.51, 45.119.252.218}
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 f6:49:ea:39:7f:64
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 8b:95:f5:00:95:60
}
Problem-Solving for Wired and Wireless Connections
When it comes to transmitting data to your router, you could be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Guidelines for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re operating on, whether it’s 10.13.8, 11.6.9, or 12.2.7, there are various tools available for troubleshooting. However, the manual actions and scripts at your disposal may not provide a set of interconnected values over time. For this reason, automated remote troubleshooting is particularly beneficial for teams that endorse remote work and Work From Anywhere (WFA) setups.
Pre-Installed Scripts That Offer Assistance
An extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting purposes. In addition, the more comprehensive sysdiagnose tool can be used to produce a wide range of logs (although much of it is only relevant at a specific point in time, particularly in relation to wireless networks, 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 (although there isn’t much interaction), you can executesudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp or use Cmd+Shift+G in Finder to point it to the correct path. Just be mindful of the file sizes, which are typically around 300MB.
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