DiagnOSe Mcs Connectivity
Understanding Internet Address Allocation
When you are connected to the Internet, you are assigned a Public IPv4 address such as 225.220.134.27 or an IPv6 address such as 2000:1e08:80e2:10e5:a833:c32c:380f:d8eb. Verifying this information is possible through https://test-ipv6.com/. However, for those who are not technically inclined, conveying or even recognizing these addresses, or even citing MAC addresses like 69:4f:04:0b:00:1a, can become prone to errors and become complex quickly. Furthermore, this method does not provide any historical data (especially for past issues).
Navigating the Internet’s Resources
To access a webpage like https://hilll.org, you first connect to a DNS server to convert the hostname (hilll) combined with the Top Level Domain (org) of the URL into an IP address like 104.236.230.30. Your computer and browser share their type with all web requests e.g. Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP. An example of a default gateway is 172.16.109.12 (usually ending in .1 or .254 depending on the scope size). This is the point where your computer routes all of its traffic. For IPv6, more detailed information can be found in how-to-fix-ipv6-connectivity/, but it can be checked on Mac or Linux with:
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 172.16.109.12 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:d69e:e6a7:2ea0:7bbf%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): {162.6.232.162, 11.191.245.37}
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 69:4f:04:0b:00:1a
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 c7:65:a3:d0:24:d5
}
Resolving Issues with Wired and Wireless Connectivity
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.
Steps for Addressing Problems on Apple macOS / OSX
Regardless of whether you are using OSX or macOS versions such as 10.14.8, 11.1.9, or 12.0.8, there are various troubleshooting tools available. However, these tools and manual actions do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool on OSX/macOS is sudo wdutil info, which dumps current wireless settings to the CLI and can also generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool provides a wide range of logs, although much of it pertains to wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively (even though there is minimal interaction), you can use sudo /usr/bin/sysdiagnose with 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 access the path. Keep in mind that the file sizes are approximately 300MB.
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