Fix MacOS IP Settings

The Fundamentals of Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 63.132.202.214, or an IPv6 address, like 2000:3b1e:3ae5:981c:60a9:2078:f09b:dca9. To verify your address, visit https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even sharing MAC addresses, such as 33:73:ba:f6:e0:52, can be prone to errors and quickly become complex. The Fundamentals of Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 63.132.202.214, or an IPv6 address, like 2000:3b1e:3ae5:981c:60a9:2078:f09b:dca9. To verify your address, visit https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even sharing MAC addresses, such as 33:73:ba:f6:e0:52, can be prone to errors and quickly become complex.

The Fundamentals of Internet Addressing

When using the Internet, you are assigned a Public IPv4 address, such as 63.132.202.214, or an IPv6 address, like 2000:3b1e:3ae5:981c:60a9:2078:f09b:dca9. To verify your address, visit https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even sharing MAC addresses, such as 33:73:ba:f6:e0:52, can be prone to errors and quickly become complex. Moreover, these addresses do not provide any historical data, particularly from past issues.

How Web Access Works and the Process of Lookups

When trying to access a website, like https://cormier.net, you first connect to a DNS server to translate the host portion (cormier) combined with the Top Level Domain (net) of the URL to an IP address, such as 226.165.188.15. With each web request, your computer and browser transmit their type, for example:
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16

Understanding the Role of Default Gateways

The default gateway is typically an address that is automatically configured via DHCP. You will receive a default gateway, like 192.168.232.67 (although they usually end in .1 or .254 depending on the scope size), and this is where your computer sends all of its traffic to be routed onward. For a deeper understanding of IPv6 connectivity, you can refer to our blog on how-to-fix-ipv6-connectivity/. On Mac or Linux, you can check this with:

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  192.168.232.67    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   fe80:336a:a072:b852:b7b1%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): {211.123.104.35, 253.169.58.207}
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 33:73:ba:f6:e0:52
  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 2c:a7:04:e2:2d:db
}

Fixing Wired and Wireless Connectivity Issues

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

Resolving Problems on Apple macOS / OSX

Regardless of the version of OSX/macOS you are running, whether it’s 10.13.9, 11.0.4, or 12.3.1, there are various troubleshooting tools available. However, these manual actions and scripts fail to provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).

Utilizing Built-in Scripts and Commands

A very useful tool on OSX/macOS is sudo wdutil info, which dumps 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 is only point-in-time in relation to wireless, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. Alternatively, you can run it interactively (although there is not much interaction) by executing sudo /usr/bin/sysdiagnose, which 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 or use Finder with Cmd+Shift+G. However, be aware of the file sizes, which are approximately 300MB.

Useful Videos

Video Title Channel
macOS Big Sur - What's New in Apple macOS 11 Hands-On Mac
Secret Mac Boot Commands - Mac Boot Key Combinations Hands-On Mac
Spotlight on Spotlight - Hands-On Mac 7 Hands-On Mac
Mac Activity Monitor - How to Troubleshoot Your Mac Hands-On Mac
Securing macOS Big Sur Hands-On Mac
Table 1.0 - Video Help



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