DiagnOSe Mcs Internet Issues
Understanding IP Addressing
When using the Internet, you are assigned an IP address such as 85.247.154.209 or 2000:2336:4ca3:cbed:d530:f0ba:16c4:28ab. You can verify this information at https://test-ipv6.com/. However, conveying these addresses, including MAC addresses like 51:93:20:b7:03:a9, to those who are not tech-savvy can be error-prone and complex. Furthermore, this method does not provide historical data, particularly during past issues.
Navigating the Internet
When attempting to access a webpage such as https://dietrich.net, the first step is to contact a DNS server to convert the host name (dietrich) in combination with the Top Level Domain (net) of the URL into an IP address, for example, 250.127.169.106. Every web request from your computer and browser includes its type, for example: Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285
Significance of Default Gateways
By default, your gateway is assigned an address automatically through DHCP. Your computer is then assigned a default gateway, such as 10.93.192.25 (typically ending in .1 or .254 depending on the scope size), to which all of its traffic is directed. For IPv6, you can find an in-depth explanation at how-to-fix-ipv6-connectivity/ and can check on Mac or Linux using the following commands:
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 10.93.192.25 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 fe80:2efe:f570:6b24:5664%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): {26.206.10.98, 222.137.66.196}
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 51:93:20:b7:03:a9
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 e1:74:27:1a:bf:8d
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of your version of OSX/macOS, whether it’s 10.14.2, 11.4.6, or 12.3.5, there are multiple 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, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing In-Built Scripts for Assistance
An extremely useful tool on OSX/macOS is the sudo wdutil info, which provides a detailed dump of current wireless related settings to the CLI and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose and be prepared for a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Be mindful of the file sizes, which are approximately 300MB more or less.
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