How Can I Test Apple IP Settings
Understanding Internet Addressing
When using the Internet, it is common to have a Public IPv4 address such as 66.7.42.45 or an IPv6 address like 2000:3869:a91e:2ebc:28e2:d9da:7fa1:e698. You can verify this information using https://test-ipv6.com/. However, conveying these addresses to non-technical individuals or even mentioning MAC addresses like c3:4a:dc:74:c4:7e can be prone to errors and quickly become complex. Furthermore, this method does not provide any historical data, particularly with past issues.
Navigating the Internet
When accessing a website such as https://olson.info, your initial step is to communicate with a DNS server to convert the host portion (olson) and the Top Level Domain (info) of the URL into an IP address, such as 243.36.120.244. In all web requests, your computer and browser also transmit their type, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway is typically an address configured automatically via DHCP. It provides a default gateway like 192.168.208.37 (although they often end in .1 or .254 based on the scope size), and it is where your computer forwards all its traffic for routing. For IPv6, detailed instructions are available at how-to-fix-ipv6-connectivity/, and you can check on Mac or Linux with:
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 192.168.208.37 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 fe80:1b72:51ef:6c22:ce45%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): {104.43.67.253, 164.71.93.181}
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 c3:4a:dc:74:c4:7e
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 ff:e9:6d:95:fa:b3
}
Resolve Issues with Wired and Wireless Networks
When dealing with data transmission at the physical and data layer, it is common to use either a wired or wireless (Wi-Fi) medium to send data to your router.
Troubleshooting Guide for Apple macOS / OSX
Regardless of the version of your OSX/macOS – be it 10.15.3, 11.3.9, or 12.1.9 – 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 valuable, especially for remote work and Work From Anywhere (WFA) teams.
Useful Built-in Scripts
One particularly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can 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 point-in-time data, 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 want to run it interactively, use sudo /usr/bin/sysdiagnose, but be aware of the large file sizes, typically around 300MB.
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