How Can I Fix MacOS IP Settings

Understanding Internet Addressing

When using the Internet, you will have either a Public IPv4 address, such as 160.111.58.233, or an IPv6 address, such as 2000:f3a7:f838:cb0d:2488:a8d7:3fe4:2ae2. You can verify this information by visiting https://test-ipv6.com/. However, for those who are not familiar with technical jargon, communicating these addresses, or even referring to MAC addresses like b4:49:2e:cd:36:e3, can quickly become complex and error-prone. Furthermore, this does not provide any historical data, especially relating to past issues.

Navigating the Web

When accessing a webpage, such as https://ritchie-will.org, your request first goes to a DNS server to translate the host portion (ritchie-will) along with the Top-Level Domain (org) of the URL into an IP address, like 125.210.245.194. Moreover, your computer and browser include its type with every web request, such as
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16

The Significance of Default Gateways

Your default gateway is typically an automatically configured address through DHCP. This gateway, usually ending in .1 or .254 depending on the scope size, such as 192.168.4.62, is where your computer sends all its traffic to be routed onwards. For IPv6, a in-depth guide can be found at how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux using the following command:

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  192.168.4.62    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:a347:448b:5f2d:ca11%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): {69.209.74.211, 71.185.21.103}
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 b4:49:2e:cd:36:e3
  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 76:3d:3f:ed:53:ae
}

Resolving Issues with Wired and Wireless Connections

When it comes to sending data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.

Troubleshooting on Apple macOS / OSX

Regardless of which version of OSX/macOS you’re using - whether it’s 10.12.6, 11.4.7, or 12.0.9 - there are various tools available for addressing issues. However, these manual actions and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for teams that promote remote work and Work From Anywhere (WFA).

Useful Built-in Scripts

One useful tool on OSX/macOS is “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. Additionally, the “sysdiagnose” tool can be used to generate a wide range of logs, although much of it relates to wireless only and is point-in-time. Running “sudo nohup /usr/bin/sysdiagnose -u &” in the background will write logs to “/var/tmp/.tar.gz” for you. If you prefer to run it interactively, you can use “sudo /usr/bin/sysdiagnose,” which will give a privacy warning. It should then open Finder in the correct location, or you can navigate to “/var/tmp” or use Finder with Cmd+Shift+G to point Finder to the path. However, be aware of the file sizes, which are approximately 300MB.

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Table 1.0 - Video Help