How To Understand OSX Internet Connection
A Guide to Understanding Internet Addressing
When using the Internet, individuals may be assigned a Public IPv4 address, such as 24.222.120.164, or an IPv6 address like 2000:4c3e:12b7:940c:c02a:1fcf:8a41:748c. This information can be verified at https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even MAC addresses like 5a:3a:34:15:69:1f, can be prone to errors and become complex. Furthermore, this method lacks the ability to provide historical data.
Navigating the Online Environment
Accessing a webpage, such as https://koelpin-bosco.org, initially involves contacting a DNS server to convert the host portion (koelpin-bosco) and the Top Level Domain (org) of the URL into an IP address, such as 51.67.91.98. Every web request from your computer and browser includes information about its type, e.g. Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Understanding the Significance of Default Gateways
The default gateway is typically an address automatically configured by DHCP, such as 192.168.171.44 (commonly ending in .1 or .254 depending on the scope size). This is where your computer directs all its traffic for further routing. For a deeper understanding of IPv6, you can explore how-to-fix-ipv6-connectivity/ or use a Mac or Linux to check.
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 192.168.171.44 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 fe80:24cd:4e81:b2e0:cd3b%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): {251.90.30.74, 111.7.161.135}
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 5a:3a:34:15:69:1f
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 af:4e:18:4a:24:87
}
Resolving Connectivity Issues: Wired vs. Wireless
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.
Troubleshooting Strategies for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using - whether it’s 10.15.5, 11.1.2, or 12.0.2 - 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 valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless related settings and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a comprehensive range of logs, although many of them are only point-in-time related to wireless, like the wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. 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 or 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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