How To DiagnOSe Mac IP Settings
The Functioning of Internet Addressing
When using the Internet, one may receive a Public IPv4 address, such as 4.23.60.74, or an IPv6 address, such as 2000:2792:7795:4a93:e61d:f982:fcac:80b7. This information can be verified at https://test-ipv6.com/. However, for those who are not tech-savvy, attempting to articulate these addresses, or even call out MAC addresses like 48:8f:97:3f:b9:10, can be prone to errors and quickly becomes complicated. Furthermore, this method does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
When accessing a webpage such as https://goldner-ward.com, the first step is to contact a DNS server to translate the host portion (goldner-ward) combined with the Top Level Domain (com) of the URL to an IP address, like 124.159.199.155. Every web request from your computer and browser includes its type e.g. Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You are provided with a default gateway, such as 192.168.75.114 (often ending in .1 or .254, depending on the scope size), and this is where your computer directs all of its traffic to be routed onwards. For IPv6, there is an in-depth analysis available on how-to-fix-ipv6-connectivity/, and you can verify it on Mac or Linux using:
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 192.168.75.114 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:f981:bbeb:3fe6:c8bd%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): {118.224.32.96, 119.81.192.229}
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 48:8f:97:3f:b9:10
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 c2:a2:d6:1c:c3:a5
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Troubleshooting
No matter which version of OSX/macOS you have - whether it’s 10.14.1, 11.6.1, or 12.3.6 - 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, especially for teams that are adapting to remote work and Work From Anywhere (WFA) setups.
Utilizing Built-in Scripts for Assistance
A highly useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although most of it is point-in-time only in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, although there is not much interaction involved. 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. Be cautious of the file sizes, which can be around 300MB more or less.
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