How Do You Test MacOS IP Settings
Understanding Internet Address Allocation
When connecting to the Internet, you are assigned either a Public IPv4 address, such as 23.104.139.141, or an IPv6 address, like 2000:81a8:f48c:c5e2:dc8a:6c6e:965d:aab2. It is possible to verify this information using the website https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even mentioning MAC addresses like a5:c0:25:70:aa:19, can be prone to errors and become complex quickly. Furthermore, this method does not provide any historical data, especially from previous issues.
Navigating the World Wide Web
In order to access a website like https://ondricka.biz, you first interact with a DNS server to translate the combination of the host portion (ondricka) and the Top Level Domain (biz) of the URL into an IP address, such as 15.200.175.192. Furthermore, your computer and browser transmit their specific type with each web request, for example:Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
By default, your gateway is usually assigned an address through DHCP. This gateway address, such as 10.70.96.110 (often ending in .1 or .254 based on the scope size), is where your computer directs all of its traffic to be forwarded onwards. For IPv6, detailed instructions can be found in the article how-to-fix-ipv6-connectivity/, but can also be checked 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 10.70.96.110 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 fe80:52f1:524c:429f:bd23%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): {237.224.158.138, 94.180.121.142}
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 a5:c0:25:70:aa:19
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 cc:5c:54:8c:4f:ab
}
Resolve Issues with Wired or Wireless Connections
When it comes to transmitting data to your router, you might be utilizing either a wired connection or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX Versions
Regardless of whether you are running OSX/macOS versions such as 10.14.4, 11.1.4, or 12.1.4, there are various troubleshooting tools available. However, these manual approaches and scripts lack the ability to provide a series of correlated values over a period of time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) concept.
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which displays the current wireless settings in the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool provides a more comprehensive approach by creating a wide range of logs, although much of it is only relevant to wireless issues, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. For an interactive option (although there is limited interaction), you can runsudo /usr/bin/sysdiagnose and it 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. However, be cautious of the file sizes, which are around 300MB or slightly more.
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