How Do You DiagnOSe OSX Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, which can be verified at https://test-ipv6.com/. Communicating these addresses or MAC addresses to non-technical individuals can be error-prone and complex, especially when considering historical data.
Navigating the World Wide Web
In order to access a specific web page, such as https://kutch.org, you must first access a DNS server to translate the host and Top Level Domain parts of the URL into an IP address. Additionally, your computer and browser send its type with all web requests, for example <br>Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A.
Significance of Default Gateways
Typically configured via DHCP, your default gateway is the address where your computer directs all of its traffic to be routed onwards, usually ending in .1 or .254 for IPv4. For IPv6, more detailed information can be found in the blog at how-to-fix-ipv6-connectivity/, and can be checked on Mac or Linux machines.
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 10.47.38.23 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 fe80:7c74:41e3:84ee:425b%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): {79.207.152.164, 168.125.79.11}
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 0f:80:b7:15:66:4d
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 83:a1:17:9e:70:25
}
Solutions for Troubleshooting Wired and Wireless Connections
When it comes to sending data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Resolving Issues on Apple macOS / OSX
No matter which version of OSX/macOS you are using, such as 10.12.9, 11.0.4, or 12.3.6, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are transitioning to remote work environments and embracing the concept of Work From Anywhere (WFA).
Pre-installed Scripts That Offer Assistance
One of the useful tools on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are specific to a point in time when it comes to wireless, just like wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and have it write logs to /var/tmp/<blah>.tar.gz, or to run it interactively with sudo /usr/bin/sysdiagnose (which will display a privacy warning), you can access the logs. 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 the file sizes are approximately 300MB.
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