How To Test Mac IP Settings
Understanding Internet Addressing
In the realm of the Internet, there exists the possibility of having a Public IPv4 address, such as 200.32.248.238, or an IPv6 address, like 2000:86df:5fa0:7be2:1b76:2abf:faf3:bbfb. This information can be verified using a website like https://test-ipv6.com/. However, for individuals who are not well-versed in technology, attempting to communicate these addresses can lead to errors and become complex. Moreover, this data does not contain any historical information, particularly from past incidents.
Navigating the World Wide Web
When visiting a website, like https://wyman-ward.info, you first access a DNS server to convert the host portion (wyman-ward) together with the Top Level Domain (info) of the URL into an IP address, such as 124.157.193.206. Each web request from your computer and browser includes its type, for example:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. It could be a default gateway like 192.0.0.189 (although they usually end in .1 or .254 based on the scope size), and this is where your computer forwards all its traffic to be routed further. For information on IPv6, an in-depth analysis can be found in how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this by 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 192.0.0.189 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:a430:1826:9304:b1e3%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): {57.238.161.9, 144.221.202.125}
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 e6:6f:e1:bd:e1:01
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 3e:c6:52:10:9b:a1
}
How to Troubleshoot and Resolve Connectivity Issues
Whether you are using a wired or wireless (Wi-Fi) medium to transmit data to your router, there are several steps you can take to troubleshoot connectivity issues at the physical and data layer.
Tips for Resolving Issues on Apple macOS / OSX
Regardless of the version of macOS or OSX you are using, such as 10.12.6, 11.4.2, or 12.3.3, there are various troubleshooting tools available. However, these manual actions and scripts may not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One 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 is more comprehensive and can generate a wide range of logs, although much of it is only a point in time snapshot in relation to wireless, similar to wdutil.
Running the command sudo nohup /usr/bin/sysdiagnose -u & will execute sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz for you. For interactive use (although there is minimal interaction), you can run sudo /usr/bin/sysdiagnose and it will provide 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 to locate the path. Keep in mind the file sizes are approximately 300MB.
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