How To Check OSX Issues
Understanding Internet Addressing
When using the Internet, your device is assigned a unique public identifier, such as 2.117.153.100 for IPv4 or 2000:4fa8:5ad0:6207:7944:f343:6532:25f2 for IPv6. Checking these addresses can be done at https://test-ipv6.com/. However, communicating these addresses, including MAC addresses like c2:4b:76:09:f9:51, can be complex and error-prone, especially for those who are not technologically inclined. Additionally, these addresses do not provide historical data, particularly during past issues.
Navigating the World Wide Web
Accessing a webpage, such as https://greenholt.org, involves connecting to a DNS server to translate the URL’s host portion (greenholt) and Top Level Domain (org) to an IP address, like 25.134.86.79. Your computer and browser send its specifications with every web request, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Network Gateways
The default gateway, usually obtained through DHCP, is an automatically configured address, such as 10.144.233.230 (commonly ending in .1 or .254 based on scope size). This is where your computer directs all traffic to be routed onwards. For IPv6, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be verified using the following method:
<br>
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 10.144.233.230 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:afa:529d:66f2:207d%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): {149.104.28.78, 185.24.198.91}
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 c2:4b:76:09:f9:51
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 5b:c0:49:35:91:3e
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Troubleshooting on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.11.3, 11.1.2, or 12.0.3, there are a variety of tools available for resolving issues. However, these manual actions and scripts do not provide a series 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 Built-in Scripts for Assistance
One useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to 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 settings at a specific point in time, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and generate logs in /var/tmp/<blah>.tar.gz, or to run it interactively by using sudo /usr/bin/sysdiagnose and navigating to the correct folder in Finder after it opens, keep in mind that the file sizes can be around 300MB.
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