How Can I Troubleshoot OSX No-access
Understanding Internet Address Formats
When using the Internet, there are two main types of addresses: IPv4 and IPv6. A public IPv4 address looks like 133.149.143.196, while an IPv6 address is formatted as 2000:4301:12af:7d46:596e:fc63:f864:f7b5. These can be verified through the test-ipv6 website. Communicating these addresses or MAC addresses like 62:55:d5:35:43:45 can be complex and error-prone, especially for those not well-versed in technology. Additionally, it does not provide any historical data regarding past issues.
Navigating the World Wide Web
When accessing a website such as https://kautzer.name, the first step is to contact a DNS server. The DNS server translates the host portion (kautzer) combined with the Top Level Domain (name) of the URL into an IP address, such as 171.244.76.54. Additionally, your computer and browser send its type with all web requests, such as Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
The Significance of Default Gateway
The default gateway is an address automatically configured via DHCP. It typically appears as 192.0.0.2 (though it usually ends in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, more detailed information can be found in our blog post, how-to-fix-ipv6-connectivity/. On Mac or Linux, you can check this with the following command:
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 192.0.0.2 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:bd6d:2a12:d47d:e56%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): {245.175.114.223, 189.240.25.14}
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 62:55:d5:35:43:45
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 78:7e:46:d4:84:41
}
Diagnosing and Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Methods for Apple macOS / OSX
No matter which version of OSX/macOS you have - whether it’s 10.12.4, 11.0.4, or 12.0.9 - 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).
Utilizing Built-in Scripts for Assistance
One extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a multitude of logs, although much of it is only relevant to wireless networks just like wdutil.
To run it in the background and write 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 be aware of the large file sizes of about 300MB.
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