Troubleshoot Mcs Issues
The Functioning of Internet Addressing
When using the Internet, individuals might have a unique Public IPv4 address like 74.218.204.18 or a different IPv6 address such as 2000:3b01:f53:5ebe:961e:cf96:e6c5:369a. These addresses can be verified from https://test-ipv6.com/. However, explaining these addresses to non-technical individuals, or even citing MAC addresses like 76:97:5c:5a:7b:f1, can be prone to errors and can become complex quite rapidly. Furthermore, this method does not offer any historical data, particularly from past issues.
Navigating the Internet
To access a website like https://mayert-koepp.com, you initially contact a DNS server in order to convert the host section (mayert-koepp) combined with the Top Level Domain (com) of the URL to an IP address, such as 129.120.148.201. Your computer and browser actually include its type with all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Predefined Gateways
Your default gateway is often an automatically configured address via DHCP. You are assigned a default gateway, such as 192.168.110.65 (although they usually end in .1 or .254 depending on the scope size), and this is where your computer sends all its traffic to be routed to other destinations. For IPv6, we cover an in-depth guide on how-to-fix-ipv6-connectivity/ but you can verify 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 192.168.110.65 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 fe80:86b1:1d3a:6614:23ea%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): {191.79.214.110, 143.222.87.50}
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 76:97:5c:5a:7b:f1
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 98:34:61:ef:e5:94
}
Resolving Connectivity Issues in Wired and Wireless Networks
When transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.11.3, 11.2.1, or 12.0.6, there are various tools available for troubleshooting. However, these tools do not provide a series of correlated values over time, making it challenging for manual actions and scripts to be effective. In such cases, automated remote troubleshooting becomes valuable, particularly for teams who have adopted remote work and Work From Anywhere (WFA).
Effective Built-in Scripts
An immensely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. Alternatively, the sysdiagnose tool offers a more comprehensive approach, generating a multitude of logs, albeit many of them being point-in-time records related to wireless, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose and navigate to the correct location in Finder, bearing in mind that the file sizes are approximately 300MB.
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