Troubleshoot OSX No-access
Explanation of Internet Addressing
When it comes to the Internet, every device has its own unique public IP address. For example, a device may have a Public IPv4 address like 221.80.220.113 or an IPv6 address like 2000:2a38:a852:e7a:5dc6:7fd2:62f0:14d4. To determine your device’s IP address, you can check it on https://test-ipv6.com/. However, for those who are not tech-savvy, communicating or dealing with these addresses, or even calling out MAC addresses like 91:ae:50:16:37:cb, can be prone to errors and can become complex. Moreover, this method does not provide any historical data, especially from the time when previous issues or problems occurred.
Navigating the Internet
Accessing a web page, such as https://roob.org, involves contacting a DNS server to convert the host portion (roob) combined with the Top Level Domain (org) of the URL into an IP address, such as 121.92.129.97. Interestingly, your computer and browser send its type along with all web requests, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. For instance, you may receive a default gateway such as 10.84.131.61 (although they typically end in .1 or .254 depending on the size of the scope). This is where your computer directs all its traffic to be routed onwards. Furthermore, for IPv6, we provide a detailed guide on how-to-fix-ipv6-connectivity/, and on Mac or Linux, you can check it 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 10.84.131.61 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:cc80:4cd1:6628:e2c3%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): {42.107.19.11, 139.234.3.33}
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 91:ae:50:16:37:cb
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 f6:fb:81:c5:2c:4c
}
Resolve Wired and Wireless Connectivity Issues
When transmitting data to your router, it is important to troubleshoot and fix any issues related to your wired or wireless (Wi-Fi) connection.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are running, whether it’s 10.13.5, 11.1.3, or 12.1.1, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of consistent values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info which provides current wireless settings to the Command Line Interface (CLI) and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can usesudo /usr/bin/sysdiagnose but beware of the file sizes, usually around 300MB.
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