How To DiagnOSe OSX Connectivity
The Functionality of Internet Addressing
When using the Internet, individuals may encounter a Public IPv4 address or an IPv6 address. These can be verified at https://test-ipv6.com/. Communicating these addresses, and even MAC addresses, can be challenging for non-technical users and can lead to errors. Additionally, these addresses do not provide historical data about previous problems.
Navigating the World Wide Web
In order to access a web page such as https://bogan.org, a DNS server must be accessed to translate the URL to an IP address. The computer and browser send their type 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)
The Significance of Default Gateways
By default, the default gateway is automatically configured through DHCP. This default gateway (although usually ending in .1 or .254) is where a computer sends all its traffic to be routed onwards. For IPv6, a detailed explanation can be found at how-to-fix-ipv6-connectivity/, or it can be checked on Mac or Linux using the 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 172.24.100.4 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 fe80:3212:baab:3a5a:fb03%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): {42.163.81.42, 213.145.186.67}
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 c1:ff:3f:89:7e:53
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 a6:39:90:dc:e0:24
}
Fixing Connectivity Issues on Wired and Wireless Networks
When it comes to sending 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
Regardless of whether you are running OSX/macOS version 10.15.2, 11.4.6, or 12.2.6, there are various tools available for troubleshooting network connectivity. However, these manual actions and scripts do not provide a series of correlated values over time, which is essential for remote troubleshooting, particularly for teams working remotely or in a Work From Anywhere (WFA) setup.
Using Built-in Scripts for Assistance
A useful tool for troubleshooting on OSX/macOS is sudo wdutil info, which provides current wireless related settings to the command line interface and can be configured to generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs related to wireless connectivity, but many of these are only point-in-time data, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can run sudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes can be around 300MB.
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