Fix OSX Issues
A Beginner’s Guide to Internet Addressing
When using the Internet, you are assigned a Public IPv4 address or an IPv6 address. These addresses can be verified by visiting https://test-ipv6.com/. However, trying to convey these addresses to individuals who are not well-versed in technology, or even identifying MAC addresses, can lead to errors and complexity. Moreover, this method does not provide any historical data, especially during previous issues.
How to Reach Websites
In order to access a website such as https://haley.io, your computer initially contacts a DNS server to translate the host portion (haley) and the Top Level Domain (io) of the URL into an IP address. Whenever you make a web request, your computer and browser send details about their type, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Understanding the Significance of Default Gateways
By utilizing the DHCP protocol, your default gateway is typically an address that is automatically configured. This gateway, which usually ends with .1 or .254 based on the scope size, is where your computer forwards all of its traffic for routing purposes. For troubleshooting IPv6 connectivity on Mac or Linux, you can refer to how-to-fix-ipv6-connectivity/ for more in-depth information.
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 192.168.22.140 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 fe80:4643:7fde:3f7b:cbc6%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): {104.80.119.196, 177.251.127.63}
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 e1:57:27:21:a2:f1
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 ad:7c:59:34:85:25
}
Resolving Issues with Wired or Wireless Connection
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) connection at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are running 10.13.3, 11.4.4, or 12.2.8 on your OSX/macOS, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes valuable, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One 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 troubleshooting logs. 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, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose, but be aware that the file sizes are typically around 300MB. After running it, Finder should open in the correct location, or you can navigate to the path /var/tmp using Finder with Cmd+Shift+G.
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