Troubleshoot Mcs Internet Issues
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 172.208.146.139 or an IPv6 address such as 2000:91b9:3b5:efc2:c75d:a107:90db:aaa1. To check your address, visit https://test-ipv6.com/. However, explaining these addresses or MAC addresses like ae:4a:47:14:d3:c2 to non-technical individuals can be prone to errors and becomes complex. It also lacks historical data, especially for past issues.
Navigating the World Wide Web
When accessing a website like https://trantow.org, your computer initially contacts a DNS server to convert the host portion (trantow) and the Top Level Domain (org) of the URL into an IP address like 0.111.81.47. Your computer and browser also send its type with each web request, for example:
Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
The Significance of Default Gateways
Your default gateway is usually automatically configured through DHCP and is represented by an address such as 192.168.67.231 (although they typically end in .1 or .254 based on the scope size). This is where your computer directs all its traffic to be routed. For IPv6, you can obtain more information in the blog how-to-fix-ipv6-connectivity/ and you can check on Mac or Linux by 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 192.168.67.231 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 fe80:20cd:3c5e:7507:7880%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): {146.192.7.199, 34.108.73.58}
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 ae:4a:47:14:d3:c2
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 cf:53:f7:eb:cb:e8
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layers.
Troubleshooting Steps for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.4, 11.2.1, or 12.3.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Native Scripts for Assistance
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings in CLI and can be configured to generate specific logs for troubleshooting. In addition, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only related to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write the logs to /var/tmp/<blah>.tar.gz. Alternatively, you can run it interactively by using sudo /usr/bin/sysdiagnose and navigate to the correct location in Finder or through the path /var/tmp with Cmd+Shift+G in Finder. Keep in mind that the file sizes are approximately 300MB.
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