Check Mac Internet Connection
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 or IPv6 address, such as 81.226.209.167 or 2000:1127:20a3:1bfc:8b64:14d6:4473:e7e4. This information can be verified at https://test-ipv6.com/. However, the challenge arises when communicating these addresses to individuals unfamiliar with technical jargon or when dealing with MAC addresses like 5b:b5:23:71:e9:c7. Furthermore, historical data is not readily available, particularly when dealing with past issues.
Navigating the World Wide Web
When attempting to access a website such as https://homenick.org, a DNS server is first contacted to translate the host portion (homenick) and the Top Level Domain (org) of the URL into an IP address, such as 101.98.131.11. Your computer and browser provide information on their type with each web request, for example:
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
The default gateway, usually obtained through DHCP, is essential for routing all traffic from your computer. This address, such as 172.31.116.209, typically ends in .1 or .254 depending on the scope size. For IPv6, comprehensive guidance is available at how-to-fix-ipv6-connectivity/, but checking on Mac or Linux can be done by:
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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 172.31.116.209 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 fe80:6a09:4a7:7a12:41a8%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): {167.91.165.83, 143.222.4.222}
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 5b:b5:23:71:e9:c7
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 9b:50:47:8d:6d:0a
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are operating on—be it 10.12.2, 11.0.2, or 12.0.3—there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of interconnected values over time. This is where automated remote troubleshooting proves beneficial, particularly for teams that embrace remote work and the Work From Anywhere (WFA) culture.
Useful Built-in Scripts
One incredibly useful tool on OSX/macOS is the “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 can be used to generate a wide range of logs, although much of it is only relevant to wireless settings at a specific point in time, similar to wdutil.
Running “sudo nohup /usr/bin/sysdiagnose -u &” will execute it in the background, and it will write logs to “/var/tmp/
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