How To DiagnOSe OSX Internet
Understanding Internet Addressing Systems
When using the Internet, individuals may be assigned a Public IPv4 address such as 221.105.161.107 or an IPv6 address like 2000:13bd:ca28:c42d:a62a:db78:e4f8:3313. This can be verified at https://test-ipv6.com/. However, for those not well-versed in technology, conveying these addresses, or even identifying MAC addresses like b3:89:e3:e4:c3:57, can be prone to errors and quickly become complex. Moreover, this method does not provide any historical data, particularly from previous issues.
Navigating the World Wide Web
When accessing a webpage such as https://harris.biz, the first step is to access a DNS server to convert the host portion (harris) combined with the URL’s Top Level Domain (biz) into an IP address like 138.10.241.28. Each web request made by your computer and browser includes its type, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address obtained through DHCP. An example of a default gateway is 172.27.49.7 (although they generally end in .1 or .254 depending on the scope size), and it is where your computer sends all its traffic to be routed onward. For IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/ and can be checked 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 172.27.49.7 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 fe80:86e:17b6:29d4:ea48%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): {103.93.217.197, 37.108.44.102}
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 b3:89:e3:e4:c3:57
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 7e:78:d0:13:28:d4
}
Resolving Connectivity Issues with Wired or Wireless Networks
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX Systems
Regardless of whether you are running OSX or macOS version 10.15.3, 11.0.7, or 12.2.5, there are various tools available for troubleshooting connectivity issues. However, these tools do not provide a comprehensive set of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for teams embracing remote work and Work From Anywhere (WFA).
Embedded Scripts for Assistance
An extremely useful tool on OSX/macOS is sudo wdutil info, which provides a detailed dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be utilized to produce a wide range of logs, although much of the information is only relevant to wireless connectivity, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. For an interactive experience (even though there isn’t much interaction), you can runsudo /usr/bin/sysdiagnose, which will provide 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 locate the path. Keep in mind that the file sizes are approximately 300MB.
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