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. 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
P.S. Tips For Remote Network and Client Support
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