Troubleshoot MacOS Internet
The Principles of Internet Addressing
In the realm of the Internet, individuals may possess a unique Public IPv4 address, such as 81.115.19.137, or an IPv6 address like 2000:6d71:f8de:aaa0:4c74:6bb2:e651:cd2d. Verification of these addresses is possible through https://test-ipv6.com/. However, conveying these addresses to non-technical individuals or identifying MAC addresses like 85:49:d3:24:96:62 can be prone to errors and become complex. Moreover, it lacks the ability to provide historical data from past issues.
Navigating the World Wide Web
To access a website, such as https://okeefe.co, the process begins by connecting to a DNS server. This server translates the host portion (okeefe) of the URL combined with the Top Level Domain (co) into an IP address, such as 89.208.190.148. Notably, all web requests from your computer and browser include the type, such as Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko.
Understanding the Significance of Default Gateways
Typically, a default gateway is automatically assigned through DHCP. You may receive a default gateway, such as 172.26.104.63 (usually ending in .1 or .254 based on the scope size), to which your computer directs all its traffic for routing. For a deeper analysis of IPv6, refer to how-to-fix-ipv6-connectivity/, or perform a check on Mac or Linux using the following method:
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 172.26.104.63 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:ca48:aeaa:1d15:2d62%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): {54.191.177.180, 200.96.47.185}
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 85:49:d3:24:96:62
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 ad:eb:f3:9e:f4:15
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data at the physical and data layer, you may be utilizing either a wired or wireless (Wi-Fi) medium to send the data to your router.
Strategies for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using - whether it’s 10.14.2, 11.6.5, or 12.1.2 - there are various troubleshooting tools available. Unfortunately, these manual actions and scripts do not provide a series 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).
Pre-Installed Scripts for Assistance
One incredibly useful 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 it is only relevant to wireless at a specific point in time, similar to wdutil.
To run it in the background and generate logs, use the command:
sudo nohup /usr/bin/sysdiagnose -u &
If you prefer to run it interactively, you can use the command:
sudo /usr/bin/sysdiagnose
Just be cautious of the file sizes, which are approximately 300MB.
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P.S. Tips For Remote Network and Client Support
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