How Can I Troubleshoot OSX Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned either a Public IPv4 address, such as 175.69.172.81, or an IPv6 address, like 2000:428b:fee9:bfdd:43a:4005:2f5e:f25a. You can verify this using the tool available at https://test-ipv6.com/. However, relaying these addresses, including MAC addresses like 79:ef:41:0b:5a:bc, to individuals who are not tech-savvy can lead to errors and confusion. Furthermore, this approach does not provide any historical data (especially for past issues).
Navigating the World Wide Web
When accessing a website, such as https://hintz-koelpin.io, the first step involves contacting a DNS server to convert the host portion (hintz-koelpin) and the Top Level Domain (io) of the URL into an IP address, such as 149.152.100.162. Moreover, your computer and browser include its type in all web requests for example, Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
Significance of Default Gateways
The default gateway is typically an address automatically configured through DHCP. This default gateway, such as 192.168.57.200 (often ending in .1 or .254 depending on the scope size), is where your computer directs all its traffic to be routed. For IPv6, more information can be found in the in-depth guide how-to-fix-ipv6-connectivity/. Additionally, on Mac or Linux, you can check this 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 192.168.57.200 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:b41b:b9cf:627c:fe02%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): {200.148.5.95, 67.198.94.250}
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 79:ef:41:0b:5a:bc
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 b3:c1:76:e9:1c:76
}
Resolve Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
No matter if you are using OSX/macOS versions like 10.15.1, 11.0.4, or 12.1.3, there are various tools available for resolving connectivity issues. However, these manual procedures and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that are actively embracing remote work and Work From Anywhere (WFA).
Pre-installed Tools for Assistance
One extremely beneficial tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also be set up to generate specific logs for troubleshooting. Additionally, for a more comprehensive approach, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is relevant to wireless settings only, similar to wdutil.
To run it in the background and have logs written to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive mode, which doesn’t require much interaction, you can run sudo /usr/bin/sysdiagnose, noting that it will prompt a privacy warning. If not run in the background, it will open Finder in the correct location or you can navigate to /var/tmp, or use Finder with Cmd+Shift+G to navigate to the path. Keep in mind that the file sizes are approximately 300MB.
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