How Do You Understand MacOS IP Settings
Understanding Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address, such as 119.254.87.222, or an IPv6 address, such as 2000:eaa6:8f59:c126:136:520f:211:ce32. The validity of these addresses can be checked at https://test-ipv6.com/. Unfortunately, communicating and dealing with these addresses, particularly for those not well-versed in technology, can be error-prone and complex. Moreover, these addresses do not provide any historical data, which can lead to difficulties especially when trying to address past issues.
Navigating the World Wide Web
When attempting to access a website, such as https://ryan-hayes.io, the process begins with querying a DNS server to translate the host portion (ryan-hayes) along with the Top Level Domain (io) of the URL, into an IP address like 69.123.219.78. It’s important to note that your computer and browser transmit their type with each web request, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
By and large, your default gateway is automatically assigned via DHCP, resulting in an address such as 172.27.175.89 (though they typically end in .1 or .254 based on the scope size). This is the designated location where your computer directs all its traffic for further routing. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available. Meanwhile, users of Mac or Linux systems can conduct a check by:
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 172.27.175.89 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 fe80:5110:f7b7:9028:8234%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): {79.220.67.38, 44.195.65.37}
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 ba:27:3d:16:48:27
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 ae:3a:c5:4d:0e:c7
}
Troubleshooting Connectivity: Wired vs Wireless
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.
Guidelines for Apple macOS / OSX Users
No matter which version of OSX/macOS you are running - whether it’s 10.13.1, 11.4.4, or 12.3.6 - 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 becomes extremely valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
One particularly useful tool on OSX/macOS is the sudo wdutil info command, 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 the information pertaining to wireless is mostly point-in-time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of approximately 300MB.
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