DiagnOSe Mcs Issues
Understanding How Internet Addressing Functions
When using the Internet, you are assigned a Public IPv4 address like 8.169.162.121 or an IPv6 address like 2000:1d43:88d8:96db:6dbd:e10c:52f1:b284. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like 5c:7f:0a:5e:58:3a, to individuals who are not well-versed in technology can be error-prone and quickly become complicated. Furthermore, this does not provide any historical data, particularly when problems have occurred in the past.
Navigating the Internet
In order to access a website such as https://hammes-treutel.net, your computer initially contacts a DNS server to convert the host portion (hammes-treutel) and the Top Level Domain (net) of the URL into an IP address, such as 194.14.186.40. Your computer and browser include its type in all web requests, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Understanding the Significance of Default Gateways
Typically, your default gateway is an automatically assigned address through DHCP. For example, you may receive a default gateway like 10.254.59.227 (although they typically end in .1 or .254 depending on the scope size), and this is the destination where your computer sends all of its traffic to be forwarded. For IPv6, you can explore more information on how-to-fix-ipv6-connectivity/ but you can verify it on Mac or Linux using:
some command here
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 10.254.59.227 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 fe80:7468:1da2:95e2:e30f%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): {253.52.233.248, 23.109.21.49}
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 5c:7f:0a:5e:58:3a
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:be:16:6a:52:8f
}
Solving Issues With Wired and Wireless Networks
When it comes to transmitting data to your router, you might rely on 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’re using OSX/macOS versions like 10.15.9, 11.6.1, or 12.1.7, there are a variety of troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time, making automated remote troubleshooting particularly useful for teams that embrace remote work or Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool for OSX/macOS users is the sudo wdutil info, which provides a dump of current wireless settings in the CLI. It can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive option for generating a wide array of logs, although much of it is limited to point-in-time information in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run (although there isn’t much interaction), use sudo /usr/bin/sysdiagnose and follow the privacy warning. If 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. Keep in mind that file sizes are typically around 300MB.
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