How Do You Check MacOS Connectivity
Explaining Internet Address Structure
When connecting to the Internet, individuals may receive either a Public IPv4 address, such as 59.10.212.217, or an IPv6 address, for example 2000:6edd:ff37:6e8b:2817:1543:e503:cba9. The process of communicating these addresses to those who are not technically inclined can be complicated and error-prone. Moreover, these addresses do not provide any historical data, which can be important when troubleshooting previous issues.
Navigating Diverse Web Addresses
In order to access a webpage, like https://hirthe.name, individuals must first access a DNS server to convert the host portion (hirthe) in combination with the Top Level Domain (name) of the URL into an IP address, such as 98.79.247.244. When making web requests, the computer and browser relay specific information, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. Commonly, this address ends in .1 or .254 depending on the scope size, like 192.0.0.236. All of the computer’s traffic is routed through the default gateway. For a deep dive into default gateways for IPv6, check out our blog post how-to-fix-ipv6-connectivity/. Additionally, users can verify this information on Mac or Linux by using the command line.
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 192.0.0.236 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 fe80:2472:6e51:87b3:71d2%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): {8.196.237.196, 207.77.210.218}
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 7f:52:5a:6c:19:27
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 c4:6e:93:6a:2b:86
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting 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 the version of OSX or macOS you are using, whether it’s 10.12.2, 11.0.2, or 12.2.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes particularly useful, especially for teams that are engaged in remote work and the Work From Anywhere (WFA) approach.
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the command line interface (CLI) and can be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose, which can generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run sysdiagnose 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 the command sudo /usr/bin/sysdiagnose, but be aware of the large file sizes, approximately 300MB.
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