How To Check OSX IP Settings
Understanding the Function of Internet Addressing
When using the Internet, your device may be assigned a Public IPv4 address such as 50.148.212.74 or an IPv6 address like 2000:6648:7b38:17f0:d3f4:4d50:52fe:c348. You can verify this information by visiting https://test-ipv6.com/. However, for those who are not technologically savvy, effectively communicating these addresses or even referencing MAC addresses like cf:01:5e:85:fd:17 can be prone to errors and become overly complex. Furthermore, this method does not provide any historical data, particularly when addressing past issues.
Navigating the Internet
In order to access a website, such as https://lockman-orn.name, your computer initially connects to a DNS server to convert the host portion (lockman-orn) along with the Top Level Domain (name) into an IP address, such as 108.7.103.138. When making web requests, your computer and browser also transmits its type, 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
Normally, your default gateway is assigned automatically through DHCP. This will result in a default gateway such as 172.20.95.103 (typically ending in .1 or .254 depending on the scope size), which serves as the central point for routing all traffic from your computer. For a more in-depth guide on IPv6 connectivity, you can refer to how-to-fix-ipv6-connectivity/, or alternatively, utilize the following checks on Mac or Linux:
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 172.20.95.103 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:a124:4b39:1383:77d4%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): {244.11.240.63, 50.55.231.110}
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 cf:01:5e:85:fd:17
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 6c:31:1e:48:b6:07
}
Resolving Issues with Wired and Wireless Connectivity
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Problems on Apple macOS / OSX Devices
Regardless of whether you are running 10.14.5, 11.3.4, or 12.0.2, there are various troubleshooting tools available for use. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting is particularly useful, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Using Pre-installed Scripts for Assistance
A very 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. In addition, the sysdiagnose tool can be used to generate a range of logs, although much of it is only relevant to wireless at a specific point in time, similar to wdutil.
When running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is not much interaction), you can runsudo /usr/bin/sysdiagnose, which will display a privacy warning. If 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 to direct Finder to the path. However, be mindful of the file sizes, which are approximately 300MB more or less.
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