How To Troubleshoot OSX Connectivity
The Functioning of Internet Addressing
When connected to the Internet, you will be assigned a Public IPv4 address, such as 247.153.243.176, or an IPv6 address, like 2000:5eaa:799:8c23:9a3f:da2:ec27:73fa. Verification can be done at https://test-ipv6.com/. However, attempting to communicate or manage these addresses, even MAC addresses like 81:f9:a4:57:6a:de, can be prone to errors and quickly become complex, especially for those who are not tech-savvy. Furthermore, this method lacks historical data, particularly from previous incidents.
Navigating the World Wide Web
To access a webpage, for example, https://lind.org, you must first utilize a DNS server to convert the host portion (lind) and the Top Level Domain (org) of the URL into an IP address, like 125.48.3.83. With every web request, your computer and browser disclose their type, as shown here: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
Your default gateway is generally an automatically assigned address through DHCP. This address, such as 192.0.0.80 (usually ending in .1 or .254 depending on the scope size), is where your computer forwards all its traffic to be routed further. For an in-depth look at IPv6, visit how-to-fix-ipv6-connectivity/, or you can verify on Mac or Linux using:
### 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 192.0.0.80 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:b9bd:ef61:285d:cea2%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): {57.111.248.21, 8.69.62.8}
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 81:f9:a4:57:6a:de
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 cf:9a:40:ae:e7:62
}
Fixing Connectivity Issues
When it comes to sending data to your router, you might encounter connectivity issues at the physical and data layer, whether you are using a wired or wireless (Wi-Fi) medium.
Troubleshooting on Apple macOS / OSX
Regardless of the version you are using, be it OSX or macOS such as 10.13.1, 11.4.4, or 12.0.1, there are various tools available for troubleshooting. However, the manual actions and scripts may not provide a series of correlated values over time. This is where automated remote troubleshooting comes in handy, especially for teams embracing remote work and Work From Anywhere (WFA).
Helpful Built-in Scripts
One of the useful tools on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time only in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. For an interactive (though minimal interaction) experience, use sudo /usr/bin/sysdiagnose, which will give 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 to point it to the path. Keep in mind that the file sizes are approximately 300MB.
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