How Can I Test Mac IP Settings
Understanding Internet Protocol Addressing
When connecting to the Internet, you will be assigned a unique public IPv4 address, such as 149.136.6.166, or an IPv6 address like 2000:198f:6c3d:9786:9dde:e41d:5728:c913. You can verify this information by visiting https://test-ipv6.com/. However, explaining these addresses, as well as MAC addresses like 9d:25:3c:9d:42:33, to individuals who are not tech-savvy can lead to errors and complications. Moreover, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
When accessing a webpage, such as https://hermiston.co, you initially connect to a DNS server to convert the host part (hermiston) combined with the Top Level Domain (co) of the URL into an IP address, such as 14.195.69.67. Moreover, your computer and browser transmit their type with all web requests, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. It assigns a default gateway like 192.168.14.96 (commonly ending in .1 or .254 depending on the scope size), where your computer directs all its traffic to be routed onwards. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, or you may verify it on Mac or Linux by:
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 192.168.14.96 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:d4f4:1473:6f34:3be1%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): {126.95.80.78, 222.229.114.101}
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 9d:25:3c:9d:42:33
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 8e:8f:ce:d2:e0:fa
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Strategies for Apple Devices Running macOS / OSX
Regardless of whether you are using OSX or macOS version 10.14.9, 11.2.5, or 12.0.8, there are a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a consistent set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that have adopted remote work and have embraced the idea of Working From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
An incredibly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless-related settings on the CLI and can also generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although many of these logs are only relevant to wireless connections, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool can be run in the background, and the logs will be written to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can run sudo /usr/bin/sysdiagnose, although it will display 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. Just be mindful of the file sizes, which are around 300MB more or less.
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