How To Fix OSX IP Settings
Explanation of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 171.46.75.202 or an IPv6 address like 2000:33ec:8920:f7a0:d48f:8c86:b184:b975. There are tools available, such as https://test-ipv6.com/, to verify these addresses. However, communicating these addresses, as well as MAC addresses like 72:cb:85:dd:8f:3b, to those who are not technologically savvy can be prone to errors and become complex. Furthermore, this method does not provide historical data, especially when dealing with past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://huels.name, the first step involves contacting a DNS server to convert the host portion (huels) combined with the Top Level Domain (name) of the URL into an IP address, for example 33.69.123.236. Additionally, your computer and browser send their specifications with every web request, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. For example, you may receive a default gateway like 172.18.199.222, although these addresses commonly end in .1 or .254 depending on the scope size. This is where your computer directs all of its traffic to be further routed. More information about IPv6 can be found in our in-depth explanation on how-to-fix-ipv6-connectivity/, but you can also check 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 172.18.199.222 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 fe80:7821:cb64:39c8:ea26%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): {239.75.83.182, 38.7.193.182}
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 72:cb:85:dd:8f:3b
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 35:c2:27:01:5f:f7
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Essential Steps for Apple macOS / OSX Users
Regardless of whether you are on OSX/macOS versions such as 10.11.6, 11.0.5, or 12.1.6, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of connected values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that adopt remote work and Work From Anywhere (WFA) policies.
Pre-installed Scripts for Assistance
A highly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs (although most of them are only relevant to wireless settings, similar to wdutil).
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, you can use sudo /usr/bin/sysdiagnose with 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 or use the path. However, be cautious of the file sizes, which are usually around 300MB.
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