How Can I DiagnOSe Mac Internet
Demystifying Internet Addressing
When it comes to the Internet, you may be assigned a Public IPv4 address, such as 186.60.26.17, or an IPv6 address, such as 2000:9442:4f30:a99d:efc9:899f:5d71:97e2. You can verify these addresses by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not tech-savvy, or even mentioning MAC addresses like 78:88:0a:e4:f3:12, can be error-prone and complex. Moreover, this method does not provide any historical data, particularly when past issues arose.
Navigating the World Wide Web
In order to access a website, for instance, https://herzog.name, you first contact a DNS server to translate the host portion (herzog) combined with the Top Level Domain (name) of the URL into an IP address, such as 175.107.160.207. Every web request made by your computer and browser includes the type of the browser, e.g. 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
Typically, your default gateway is an automatically configured address through DHCP. Most often, you receive a default gateway like 10.8.227.27 (although they usually end in .1 or .254, depending on the scope size), and this is where your computer directs all of its traffic in order to be rerouted further. For IPv6, there is a comprehensive guide available on how-to-fix-ipv6-connectivity/, but you can verify it on Mac or Linux by 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 10.8.227.27 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 fe80:2db6:d945:e35f:f1a6%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): {121.186.53.171, 50.72.88.227}
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 78:88:0a:e4:f3:12
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 74:e0:34:ac:75:03
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting 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 Users
No matter which version of OSX/macOS you are currently using - whether it’s 10.12.7, 11.0.7, or 12.3.2 - there are various tools available for troubleshooting. However, these manual actions and scripts fail to provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that embrace remote work and Work From Anywhere (WFA).
Effective Built-in Commands for Troubleshooting
One incredibly useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless-related settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the more comprehensive sysdiagnose tool can be used to generate a wide range of logs related to wireless, although much of it is only relevant at a specific point in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (despite minimal interaction), you can use sudo /usr/bin/sysdiagnose and it will display 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. Keep in mind that the file sizes can reach about 300MB or so.
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