DiagnOSe Mac Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address like 158.159.240.94 or an IPv6 address like 2000:57f0:7173:eef2:7084:426a:ad6e:90e5. You can verify this information by visiting https://test-ipv6.com/. However, sharing or communicating these addresses, as well as MAC addresses like 25:8a:f1:52:6a:bc, can be prone to errors and quickly become complex, especially for those not well-versed in technology. Moreover, this method does not provide any historical data on previous issues.
Navigating the World Wide Web
When accessing a website such as https://marks-jones.org, your computer first contacts a DNS server to translate the host portion (marks-jones) along with the Top Level Domain (org) of the URL into an IP address like 70.54.135.62. Every web request sent by your computer and browser includes its type, for example: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Understanding the Significance of Default Gateways
Your default gateway is typically an address configured automatically through DHCP. This gateway may appear as 10.9.50.188 (although it often ends in .1 or .254 depending on the scope size), and it is where your computer forwards all its traffic to be routed further. To address issues related to IPv6 connectivity, you can refer to our detailed guide at how-to-fix-ipv6-connectivity/, or check 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 10.9.50.188 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 fe80:3032:83d5:7fb9:67fe%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): {51.3.47.143, 156.170.224.106}
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 25:8a:f1:52:6a: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 47:33:0a:42:53:81
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps for Troubleshooting on Apple macOS / OSX
Whether you are using version 10.12.3, 11.0.1, or 12.2.3 of OSX/macOS, there are various tools available for troubleshooting. Unfortunately, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Utilizing Pre-Installed Scripts for Assistance
A useful tool on OSX/macOS is sudo wdutil info, which provides a dump to the CLI of current wireless-related settings and can be configured to generate specific logs for troubleshooting. Additionally, the more comprehensive sysdiagnose tool can be used to generate a wide range of logs (although much of it is only relevant to the present time, similar to wdutil).
To run it in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (although there is not much interaction), use the command sudo /usr/bin/sysdiagnose but be prepared for file sizes of about 300MB.
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