How To Understand Mac IP Settings
Understanding Internet Address Allocation
When connecting to the Internet, you are assigned a unique public IP address, such as 80.252.165.167 or 2000:14e2:3e63:db0b:bfec:3d23:74d9:8cf1. To verify your assigned IP address, you can visit https://test-ipv6.com/. However, for those who are not well-versed in technology, communicating these addresses, including MAC addresses like 43:8e:4e:85:ce:f9, can quickly become complex and error-prone. Furthermore, these addresses do not provide historical data, which is particularly useful for troubleshooting past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://gottlieb.org, your computer first contacts a Domain Name System (DNS) server to translate the host portion (gottlieb) along with the Top Level Domain (org) of the URL into an IP address, such as 112.78.51.8. With every web request, your computer and browser also include its type, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway is typically an automatically configured address provided through DHCP. This gateway, such as 10.49.174.22 (although it usually ends in .1 or .254, depending on the scope size), is where your computer forwards all of its traffic to be routed onwards. For IPv6, detailed instructions on how to check default gateways on Mac or Linux can be found in our how-to-fix-ipv6-connectivity/ guide.
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 10.49.174.22 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 fe80:5809:3841:4a44:73a5%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): {146.39.150.96, 139.20.160.58}
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 43:8e:4e:85:ce:f9
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 dc:32:53:e0:5f:a8
}
Resolving Issues with Wired and Wireless Connections
When transmitting data to your router, it’s important to troubleshoot and fix any issues that may arise with wired or wireless (Wi-Fi) connections at the physical and data layers.
Action Steps for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re currently using, whether it’s 10.14.4, 11.3.5, or 12.0.6, there are a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes particularly valuable, especially for teams that adopt remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
One highly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Another, more comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs (although much of it is point-in-time only in relation to wireless, similar to wdutil).
To run it in the background and generate logs in /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (although there is not much interaction), use the command sudo /usr/bin/sysdiagnose and note the privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp using Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB or less.
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