How Can I Troubleshoot MacOS IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 100.203.242.250, or an IPv6 address, such as 2000:99e1:88b0:7a7d:2874:57d8:7058:a857. These addresses can be verified by visiting https://test-ipv6.com/. However, for individuals who are not familiar with technology, conveying and working with these addresses, or even referring to MAC addresses like 98:3e:59:ef:41:ed, can be prone to errors and quickly become complex. Additionally, this method does not provide historical data, especially for past issues.
Navigating the World Wide Web
To access a web page, for example, https://kautzer.com, you first access a DNS server to convert the host part (kautzer) and the Top Level Domain (com) of the URL into an IP address, such as 53.66.117.109. Your computer and browser include its type in 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
The default gateway is typically an automatically configured address through DHCP. You are assigned a default gateway, such as 10.163.108.177 (typically ending in .1 or .254 depending on the scope size), and this is where your computer directs all its traffic to be routed. For IPv6, a detailed explanation is available in how-to-fix-ipv6-connectivity/, and you can check on Mac or Linux using the following command:
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 10.163.108.177 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 fe80:4d11:5d1b:bf8f:dcf0%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): {162.242.170.166, 224.169.138.112}
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 98:3e:59:ef:41:ed
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 4b:e0:87:44:df:1f
}
Resolving Issues with Wired and Wireless Connections
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.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are operating on, whether it’s 10.11.7, 11.4.6, or 12.1.7, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting proves to be particularly useful, especially for teams that practice remote work and Work From Anywhere (WFA).
Utilizing Pre-installed Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless-related settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it pertains to wireless settings at a specific point in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will give a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp and use Finder with Cmd+Shift+G to point Finder to the path. However, be mindful of the file sizes, which are around 300MB more or less.
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