Fix OSX Connectivity
Understanding Internet Addressing
When accessing the Internet, you will be assigned a Public IPv4 address such as 20.118.50.255, or an IPv6 address like 2000:3d24:9161:41a4:9c1f:a755:af64:ba94. These can be verified through https://test-ipv6.com/, but for those unfamiliar with tech jargon, communicating or referencing these addresses, or even MAC addresses such as 67:c3:8a:e6:0d:d0, can quickly become complicated and error-prone. Moreover, this method does not provide historical data, especially when previous issues occurred.
Navigating the World Wide Web
When trying to access a website like https://hoeger.biz, you begin by reaching out to a DNS server to translate the host part (hoeger) combined with the Top Level Domain (biz) of the URL into an IP address like 98.161.9.187. Your computer and browser also send their type alongside all web requests, such as: 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
The default gateway is typically an automatically configured address via DHCP. You are assigned a default gateway like 192.168.194.183 (often ending in .1 or .254 depending on the scope size), which is where your computer sends all its traffic to be routed onwards. For IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available, but Mac or Linux users can check using 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 192.168.194.183 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 fe80:941:dabb:3270:27af%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): {100.79.13.228, 183.31.170.79}
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 67:c3:8a:e6:0d:d0
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 0c:9b:8d:ff:6b:8e
}
Resolve Connectivity Issues with Wired and Wireless Networks
When transferring data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Irrespective of whether you are using OSX/macOS versions such as 10.14.2, 11.0.8, or 12.1.6, 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 valuable, particularly for teams that are engaged in remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings to the CLI, and can also be configured to generate specific logs for troubleshooting. Another more comprehensive tool is the sysdiagnose, which can generate a wide range of logs, although most of the data is only relevant to wireless settings.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and create logs in /var/tmp/<blah>.tar.gz. For an interactive run, you can use sudo /usr/bin/sysdiagnose and navigate to the correct location. Keep in mind that the file sizes are around 300MB.
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