How To Troubleshoot OSX Internet
Understanding Internet Addressing
When using the internet, you are assigned a unique public IP address, which can be either an IPv4 address, like 59.212.131.245, or an IPv6 address, like 2000:775c:c6da:6a7e:2379:f505:29b0:e1f8. The website https://test-ipv6.com/ can be used to verify this information. However, for those who are not familiar with technical terminology, communicating these addresses, or even referencing MAC addresses such as 9b:ec:cb:15:1c:45, can be difficult and prone to errors. Additionally, this method does not provide any historical data, particularly in relation to past issues that have occurred.
Navigating the World Wide Web
In order to access a website such as https://kessler.name, the first step is to connect to a DNS server to convert the host component (kessler) along with the Top Level Domain (name) of the URL into an IP address, such as 127.216.112.55. When making web requests, your computer and browser also send their data type, for example: Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
The default gateway is typically an automatically assigned address through DHCP. This gateway, such as 10.121.139.20 (usually ending in .1 or .254 based on scope size), serves as the destination for all the traffic that your computer transmits for further routing. A detailed guide on how to address IPv6 connectivity issues can be found at how-to-fix-ipv6-connectivity/. If you are using Mac or Linux, you can verify this by running:
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 10.121.139.20 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 fe80:9b02:6a15:272e:63cd%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): {63.125.158.167, 220.124.181.218}
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 9b:ec:cb:15:1c:45
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 c7:c6:5e:fc:85:10
}
Resolve Connectivity Issues for Wired and Wireless Networks
When transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Methods for Apple macOS / OSX Devices
Regardless of the version of OSX/macOS you are running, whether it’s 10.15.5, 11.1.1, or 12.1.9, there are various tools available for troubleshooting connectivity issues. Unfortunately, the 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 adopt remote work and Work From Anywhere (WFA) practices.
Effective Built-in Tools for Troubleshooting
One useful tool on OSX/macOS is the “sudo wdutil info,” which provides a dump to the CLI of current wireless related settings and can also be configured to generate specific logs for troubleshooting. Additionally, the “sysdiagnose” tool can be used to generate a wide range of logs, although many of them are only related to wireless settings and are point-in-time. Running “sudo nohup /usr/bin/sysdiagnose -u &” in the background will generate logs in “/var/tmp/
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