How Do You DiagnOSe MacOS Connectivity
Understanding Internet Address Assignments
When using the Internet, users are assigned various types of IP addresses, such as Public IPv4 or IPv6 addresses. These addresses can be verified through the use of platforms like https://test-ipv6.com/. However, conveying these addresses, especially to those not well-versed in technology, can be complex and error-prone. Furthermore, historical data on previous issues is not easily accessible.
Navigating the World Wide Web
Accessing a website like https://dickens.org involves a process where a DNS server translates the host portion of the URL, along with the Top Level Domain, into an IP address. Each web request also includes detailed information about the user’s computer and browser, such as Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts).
The Significance of Default Gateways
The default gateway, typically obtained through DHCP, serves as the designated address for routing all outgoing traffic from a computer. For IPv6 connectivity issues, a comprehensive guide is available at how-to-fix-ipv6-connectivity/. Alternatively, users can perform checks on Mac or Linux systems using specific commands.
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 192.0.0.122 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:c448:d947:87be:fe4c%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): {230.67.7.23, 118.83.222.10}
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 51:75:91:59:99:d5
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 62:db:0c:4c:24:7c
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you have, whether it’s 10.12.2, 11.0.1, or 12.0.5, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One tool that macOS users can rely on is sudo wdutil info, which provides a dump of current wireless settings to the command line interface and can also generate specific logs for troubleshooting purposes. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs related to wireless issues, although the majority of the data is only relevant at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. For an interactive approach (although there is minimal interaction), you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point Finder to the path. However, be mindful of the file sizes, which are around 300MB more or less.
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