How To DiagnOSe OSX Internet Connection
The Functioning of Internet Addressing
When using the Internet, you are assigned a specific IP address, such as 242.202.122.60 for IPv4 or 2000:dcd:b0a:5bc7:9c5b:1d3f:364a:b0ea for IPv6. You can verify this at https://test-ipv6.com/. However, for those who are not tech-savvy, communicating or identifying these IP addresses, or MAC addresses like 00:be:5a:66:62:49, can be prone to errors and quickly become complicated. Additionally, this does not provide any historical data, especially when it comes to past issues.
Navigating the Internet
Accessing a website such as https://murray-moore.net involves initially connecting to a DNS server to convert the host name part (murray-moore) combined with the Top Level Domain (net) of the URL into an IP address, such as 78.158.241.194. Your computer and browser include specific information with all web requests, such as 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
Your default gateway is typically an address that is automatically configured through DHCP. This default gateway, such as 10.129.91.36 (usually ending in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed to its final destination. For IPv6, there is an in-depth explanation available here, and you can verify this on Mac or Linux using the following commands:
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 10.129.91.36 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 fe80:7fd2:482e:4817:bc86%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): {31.100.219.124, 151.215.58.38}
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 00:be:5a:66:62:49
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 99:51:f1:63:19:1c
}
Fixing Connectivity Issues for Wired and Wireless Networks
When dealing with data transmission at the physical and data layer, it’s important to consider whether you are using a wired or wireless (Wi-Fi) medium to send the data to your router.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS version 10.13.1, 11.1.7, or 12.0.1, there are various troubleshooting tools available. However, these manual actions and scripts may not provide a continuous stream of correlated values over time. This is where the importance of automated remote troubleshooting becomes evident, especially for teams that have embraced remote work and Work From Anywhere (WFA).
Utilizing Pre-Installed Scripts for Assistance
One of the useful tools available on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the command line interface. This command can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool offers a more comprehensive approach by generating a wide range of logs, although many of these are point-in-time records related to wireless issues, similar to wdutil.
For running the sysdiagnose tool in the background and writing the logs to /var/tmp/<blah>.tar.gz, the following command can be used: sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for an interactive run (although there is minimal interaction), the command sudo /usr/bin/sysdiagnose can be used, which will prompt a privacy warning. When not run in the background, this command should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. It’s important to note that the file sizes can be around 300MB, give or take.
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