Fix Mcs No Access
Understanding Internet Addressing
When using the Internet, you will be assigned a Public IPv4 or IPv6 address, such as 115.232.25.99 or 2000:f46d:1dc7:14f0:a708:ac86:88df:8f80. These addresses can be verified at https://test-ipv6.com/. However, attempting to relay these addresses, or even MAC addresses like 77:2e:90:91:a9:39, to those who are not technically inclined can be prone to errors and becomes complex quickly. Furthermore, this method does not provide any historical data, especially from previous issues.
Navigating the World Wide Web
In order to access a website like https://abbott-kessler.name, your computer initially connects to a DNS server to convert the host part (abbott-kessler) along with the Top Level Domain (name) of the URL to an IP address like 58.67.174.232. Your computer and browser includes its type in all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway is typically an automatically assigned address via DHCP. You will receive a default gateway like 192.0.0.144 (although they generally end in .1 or .254 depending on the scope size), which is where your computer directs all of its traffic to be routed further. For more details on IPv6, you can refer to our in-depth guide at how-to-fix-ipv6-connectivity/, or you can verify it 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 192.0.0.144 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 fe80:7f5c:b7f2:c0be:3825%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): {122.63.62.42, 0.85.63.22}
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 77:2e:90:91:a9:39
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 7c:51:9d:90:39:9f
}
Resolving Issues with Wired and Wireless Connection
When transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of which version of OSX/macOS you are using, whether it’s 10.13.4, 11.4.7, or 12.3.1, there is a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool in OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless 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 sudo /usr/bin/sysdiagnose (although there is not much interaction) and beware of the large file sizes of about 300MB.
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