How Do You DiagnOSe Mac Internet
Understanding How Internet Addresses Function
When using the Internet, you are assigned a Public IPv4 address, such as 198.8.104.165, or an IPv6 address, like 2000:bcad:7cb6:2b26:fbe5:b4ad:48ee:1dd3. You can verify this at https://test-ipv6.com/. However, for individuals who are not well-versed in technology, communicating these addresses, or even mentioning MAC addresses like 2c:37:bc:09:f3:dd, can be prone to mistakes and becomes complex fairly quickly. Moreover, this does not provide any historical data, especially for past issues.
Navigating the Internet
When attempting to access a website, such as https://borer.co, you first connect to a DNS server to decode the host section (borer) coupled with the Top Level Domain (co) of the URL, into an IP address like 195.205.150.24. Your computer and browser actually transmits its type with all web requests, such as Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You receive a default gateway like 10.183.17.207 (although they generally end in .1 or .254 depending on the scope size) and this is where your computer sends all its traffic to be routed onwards. For IPv6, we have an in-depth discussion on how-to-fix-ipv6-connectivity/ but you can perform a check on Mac or Linux with:
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 10.183.17.207 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 fe80:512:ac3d:cb1d:ae5b%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): {235.134.108.149, 135.192.174.222}
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 2c:37:bc:09:f3:dd
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 56:66:60:a9:d0:25
}
Resolve Connectivity Issues for Wired or Wireless Connections
Whether you are using a wired or wireless (Wi-Fi) medium to transmit data to your router, connectivity issues can arise at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of your version of OSX/macOS, whether it’s 10.15.9, 11.1.8, or 12.0.6, there are various tools available for troubleshooting. However, these tools do not provide a series of correlated values over time, making it difficult to track issues. This is where automated remote troubleshooting becomes valuable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely helpful tool on OSX/macOS is the sudo wdutil info command which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of this information is only relevant at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and generate logs, use the command sudo nohup /usr/bin/sysdiagnose -u &, and it will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose but be cautious of the file sizes, which can be around 300MB.
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P.S. Tips For Remote Network and Client Support
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