Troubleshoot Mac Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 222.186.12.33, or an IPv6 address like 2000:9580:40c7:5a25:c565:4f59:856a:ce48. Verification of these addresses can be done at https://test-ipv6.com/. However, for those unfamiliar with technology, communicating these addresses, including MAC addresses like 33:b6:ef:99:0a:cb, can be error-prone and complex. Moreover, this method lacks access to historical data, particularly when dealing with past issues.
Navigating the World Wide Web
In order to access a webpage such as https://fay.info, the process involves initially accessing a DNS server to translate the URL’s host portion (fay) combined with the Top Level Domain (info) into an IP address like 195.150.70.189. Whenever making web requests, your computer and browser also communicate their type, such as Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Usually, a default gateway is automatically configured through DHCP, providing an address like 172.28.109.12 (typically ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, a detailed guide can be found at how-to-fix-ipv6-connectivity/, with instructions for checking on Mac or Linux.
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 172.28.109.12 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 fe80:2aa9:aeb:fc1d:7304%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): {1.156.152.134, 232.67.223.128}
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 33:b6:ef:99:0a:cb
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 96:c8:ad:ea:41:ae
}
Resolving Connectivity Issues in Wired and Wireless Networks
When it comes to transferring 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 are running - whether it’s 10.11.3, 11.3.7, or 12.1.2 - there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that adopt remote work and Work From Anywhere (WFA) practices.
Useful Built-in Tools for Troubleshooting
One highly beneficial tool on OSX/macOS is sudo wdutil info, 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 offers a more comprehensive option for generating various logs, although much of the information is only relevant to wireless at a specific point in time, similarly to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which 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 Cmd+Shift+G in Finder. Just keep in mind that the file sizes are around 300MB or so.
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