How Can I Troubleshoot OSX IP Settings
Understanding How Internet Addressing Functions
When using the Internet, you can be assigned a Public IPv4 address, such as 133.88.119.201, or an IPv6 address, like 2000:18ef:33c5:67e9:36c4:dda0:5de6:a971. You can verify this information by visiting https://test-ipv6.com/. However, communicating these addresses, or even referring to MAC addresses like 75:3f:b3:36:31:e7, can be prone to errors and quickly become complex for those who are not familiar with technical jargon. Moreover, this approach does not provide any historical data (especially from previous incidents).
Navigating the World Wide Web
In order to access a website such as https://mohr-simonis.com, you first connect to a DNS server to convert the host portion (mohr-simonis) along with the Top Level Domain (com) of the URL to an IP address, such as 246.251.121.58. Your computer and browser sends its type along with all web requests, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Your default gateway is typically an address that is automatically assigned through DHCP. This address, such as 10.54.129.236 (usually ending in .1 or .254 depending on the scope size), is where your computer sends all of its traffic to be forwarded. For IPv6, a detailed analysis can be found at how-to-fix-ipv6-connectivity/, but you can also verify this on Mac or Linux by using:
route -A inet6
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 10.54.129.236 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 fe80:7ab1:afb5:f45a:c8ea%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): {129.197.217.244, 238.115.114.105}
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 75:3f:b3:36:31:e7
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 ed:9d:de:ee:b7:31
}
Resolve Connectivity Issues for Wired and Wireless Networks
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.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS version 10.14.3, 11.6.4, or 12.3.1, there are various troubleshooting tools available. However, performing manual actions and running scripts may not provide a comprehensive set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that operate remotely and follow a Work From Anywhere (WFA) concept.
Useful Built-in Utilities
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is related to wireless settings and is only available at a specific point in time, similar to wdutil.
To run sysdiagnose 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, you can use the command: sudo /usr/bin/sysdiagnose, which will show a privacy warning. Running it in this manner should open Finder in the correct location, or you can navigate to /var/tmp, or use Finder with Cmd+Shift+G to point Finder to the path. Keep in mind that the file sizes typically range around 300MB.
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