How Can I DiagnOSe OSX Connectivity
Understanding Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 address such as 80.36.13.207 or an IPv6 address like 2000:f331:e870:d485:7316:8071:7a91:178b. These addresses can be verified using https://test-ipv6.com/. However, for those not well-versed in technology, relaying and communicating these addresses, as well as MAC addresses such as a7:15:cd:7d:3c:b8, can become prone to errors and complex. Furthermore, this does not provide historical data, especially when dealing with past issues.
Navigating the Internet
Accessing a website, such as https://cremin.com, involves initially contacting a DNS server to convert the host portion (cremin) combined with the Top Level Domain (com) of the URL into an IP address like 220.185.206.181. Furthermore, your computer and browser include its type in all web requests, e.g. Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
Understanding the Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP. Typically, you receive a default gateway like 192.168.27.73 (commonly ending in .1 or .254 depending on the scope), and this is where your computer sends all its traffic for further routing. For IPv6, detailed information can be found in our article on how-to-fix-ipv6-connectivity/, and it can be checked on Mac or Linux using the following method:
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 192.168.27.73 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 fe80:5b5f:b787:4bc0:e3c0%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): {17.186.241.114, 53.165.201.53}
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 a7:15:cd:7d:3c:b8
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 59:81:cb:14:94:ce
}
Resolving Connection Issues for Wired and Wireless Networks
When it comes to transmitting data, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer to send data to your router.
Troubleshooting Tips for Apple macOS / OSX
No matter which version of OSX/macOS you are operating - whether it’s 10.11.5, 11.4.9, or 12.1.1 - there are various tools available for troubleshooting. 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 embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One incredibly 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 at a specific point in time, just like wdutil.
To run sysdiagnose in the background and generate logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but beware of the large file sizes of about 300MB. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp manually. Just be cautious of the file sizes, which can be around 300MB.
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