How To DiagnOSe MacOS IP Settings
Functioning of Internet Addresses
When using the internet, you are assigned with a Public IPv4 address such as 215.245.118.172 or an IPv6 address like 2000:136d:7767:56c6:166a:a97b:ffbf:be4c. To verify this, visit https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying these addresses can be prone to error and quickly become complex. Moreover, it does not provide any historical data, especially when addressing past issues.
Navigating the Internet
In order to access a webpage like https://paucek-sanford.io, the first step is to contact a DNS server to convert the host portion (paucek-sanford) along with the Top Level Domain (io) of the URL to an IP address such as 91.147.40.146. With each web request, your computer and browser include details like its type, for example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Significance of Default Gateways
Typically, your default gateway is an automatically assigned address through DHCP. A default gateway, such as 192.0.0.123 (usually ending in .1 or .254 depending on the scope size), is where your computer directs all its traffic for further routing. For IPv6, a detailed analysis is provided in how-to-fix-ipv6-connectivity/. Verification on Mac or Linux can be performed 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 192.0.0.123 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:bbf6:2f61:e72e:f049%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): {181.63.250.167, 223.201.136.9}
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 14:e1:6a:92:91:09
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 b0:70:08:8e:ba:df
}
Fixing Connectivity Issues in Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX Systems
Regardless of the version of OSX/macOS you are using, whether it’s 10.11.7, 11.2.5, or 12.2.7, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes beneficial, particularly for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Tools for Troubleshooting
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs, use the command sudo nohup /usr/bin/sysdiagnose -u &. It will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, which will prompt 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. But be aware of the file sizes, which are approximately 300MB.
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