How Do You Fix MacOS IP Settings
Demystifying Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 126.219.248.104 or an IPv6 address like 2000:6c8c:766c:389a:91c3:f484:69b5:4b57. You can verify this information at https://test-ipv6.com/. However, explaining or handling these addresses, and even MAC addresses like df:b8:94:76:92:a2, can be challenging for those unfamiliar with technology. Moreover, it does not provide any historical data, especially for previous issues.
Understanding Web Access
When accessing a web page like https://kub.com, the first step is to access a DNS server to translate the host portion (kub) combined with the Top Level Domain (com) of the URL to an IP address such as 27.35.189.38. Additionally, your computer and browser send its type along with all web requests, for example:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Exploring the Significance of Default Gateways
Your default gateway is typically an automatically assigned address via DHCP, such as 192.0.0.151 (although they usually end in .1 or .254 depending on the scope size). This is the destination where your computer sends all its traffic to be routed onwards. For IPv6, in-depth information is available at how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux with:
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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 192.0.0.151 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 fe80:50fb:bb89:eaf6:550%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): {127.123.12.7, 89.149.173.65}
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 df:b8:94:76:92:a2
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 57:54:05:52:59:35
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you could be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX or macOS you are using - whether it’s 10.15.6, 11.6.5, or 12.2.7 - there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely useful tool for OSX/macOS users is the sudo wdutil info, which provides a dump of current wireless related settings to the CLI and can be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can also be used to generate a wide range of logs, although much of it is only related to wireless settings at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, but be aware of the rather large file sizes of about 300MB. After running the interactive command, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder or utilize the shortcut Cmd+Shift+G.
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