DiagnOSe OSX IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 230.71.11.202, or an IPv6 address, like 2000:3646:d709:ff03:92fd:9315:96e5:2ee2. To verify your address, visit https://test-ipv6.com/. However, conveying these addresses to those not familiar with technology, or even mentioning MAC addresses like a5:85:7e:e4:4b:48, can be prone to errors and quickly become complex. Furthermore, this method does not provide any historical data, particularly when dealing with past issues.
Navigating the World Wide Web
When attempting to access a webpage, such as https://fay.org, you first connect to a DNS server to translate the host portion (fay) and the Top Level Domain (org) of the URL into an IP address, such as 82.218.204.210. Your computer and browser automatically send their type with all web requests, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
The Significance of Default Gateways
Your default gateway is typically an address configured automatically via DHCP. This gateway, such as 10.65.15.243 (usually ending in .1 or .254 depending on scope size), is where your computer sends all its traffic to be routed onward. For more information on setting up IPv6, visit our in-depth guide at how-to-fix-ipv6-connectivity/. Alternatively, you can check on Mac or Linux 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 10.65.15.243 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 fe80:83a2:49ff:95e5:cd18%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): {104.99.91.101, 90.210.111.163}
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 a5:85:7e:e4:4b:48
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 fd:a9:3a:39:31:47
}
Resolving Issues with Wired or Wireless Connections
When transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Troubleshooting on Apple macOS / OSX
Irrespective of the version of OSX/macOS you are using, be it 10.12.5, 11.0.9, or 12.1.2, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
A highly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it is only relevant to wireless at a specific point in time, similar to the wdutil tool.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively with a privacy warning, you can use the command sudo /usr/bin/sysdiagnose. 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 keep in mind that the file sizes are approximately 300MB.
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