Understand MacOS IP Settings
The Functionality of Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 122.9.186.94, or an IPv6 address, like 2000:e634:48e2:66a5:513f:baab:1ec5:cb33. You can verify this information by visiting https://test-ipv6.com/. However, explaining or sharing these addresses, as well as MAC addresses like a0:9e:4b:4f:eb:67, can be a challenging task, especially for individuals who are not tech-savvy. Moreover, this method does not provide any historical data, particularly during previous occurrences of issues.
Navigating the World Wide Web
To access a website, such as https://emmerich.org, your computer first contacts a DNS server to convert the domain name (emmerich) combined with the Top Level Domain (org) into an IP address, like 30.159.232.195. When making web requests, your computer and browser also include information about their type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
Understanding the Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. This gateway, such as 192.0.0.16 (commonly ending in .1 or .254 based on scope size), is responsible for routing all of your computer’s traffic. Detailed instructions for checking default gateways for IPv6 can be found in our in-depth guide on how-to-fix-ipv6-connectivity/, and the process can also be performed on Mac or Linux systems.
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 192.0.0.16 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 fe80:412c:cdb9:8e6b:9b04%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): {118.118.2.17, 221.96.17.134}
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 a0:9e:4b:4f:eb:67
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 37:a7:85:cf:b7:e3
}
Solutions for Resolving Connectivity Issues
When it comes to transferring data to your router, you may encounter issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Steps for Troubleshooting on Apple macOS / OSX
Regardless of whether you are using OSX or macOS version 10.12.8, 11.4.4, or 12.0.9, there are various tools available for troubleshooting. However, the manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, particularly for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Tools
On OSX/macOS, a useful tool for troubleshooting is sudo wdutil info, which provides a dump of current wireless related settings to the command line interface. It can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool offers a more comprehensive range of logs (although much of it is only related to wireless settings like wdutil).
To run sysdiagnose in the background and generate logs at /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use sudo /usr/bin/sysdiagnose and follow the privacy warning. Be cautious of the large file sizes, which can be around 300MB.
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