Fix Mcs Issues
Understanding the Functioning of Internet Addresses
When using the Internet, you may have a Public IPv4 address such as 108.162.8.162 or an IPv6 address like 2000:7b48:5d72:e633:6a4e:6233:b033:a17a. It is possible to verify this by visiting https://test-ipv6.com/. However, it can be difficult for individuals who are not technology-savvy to convey these addresses, or even refer to MAC addresses such as a9:04:b0:a5:8d:26. Furthermore, this method does not provide any historical information, particularly related to previous issues.
Navigation on the World Wide Web
When attempting to access a website like https://wyman.io, the first step involves contacting a DNS server to convert the host name (wyman) along with the Top Level Domain (io) of the URL to an IP address, for example 126.38.173.73. In all web requests, your computer sends its type, for instance Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured through DHCP. This address, such as 192.168.37.137 (although they often end in .1 or .254 based on the scope size), is where your computer routes all of its traffic. For IPv6, detailed instructions can be found in the article how-to-fix-ipv6-connectivity/, and this can be checked on Mac or Linux using the following command.
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 192.168.37.137 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 fe80:1c6b:f2d9:d447:e120%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): {107.47.229.15, 191.254.59.62}
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 a9:04:b0:a5:8d:26
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 c0:57:c7:79:32:6c
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or a 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 10.14.5, 11.2.4, or 12.2.1, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time, making automated remote troubleshooting a valuable option, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts to Assist
A valuable tool for OSX/macOS users is the sudo wdutil info command, which provides a dump to the CLI of current wireless settings and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to wireless (although most are point-in-time only, similar to wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for the user. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, which will provide a privacy warning and open Finder in the correct location. Users can also navigate to /var/tmp or use Finder with Cmd+Shift+G to navigate to the path, keeping in mind that the file sizes are approximately 300MB.
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