DiagnOSe Mac Internet
Explanation of Internet Addressing
When connecting to the Internet, you will receive a Public IPv4 address such as 255.157.218.91 or an IPv6 address like 2000:c77c:ebc:d910:3103:fd9a:833e:3637. The website https://test-ipv6.com/ can be used to verify these addresses. However, for those who are not technologically inclined, communicating these addresses or referring to MAC addresses like 22:e7:ba:f4:2b:e0 can be prone to errors and become complex. Moreover, this method does not provide any historical data, especially regarding past issues.
How to Connect to the Internet
When accessing a website such as https://hansen-glover.io, the first step is to connect to a DNS server to convert the host portion (hansen-glover) along with the Top Level Domain (io) of the URL to an IP address like 221.185.221.169. A computer and browser will also include the type of the request in every web request, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured via DHCP. A default gateway, such as 172.16.235.190 (usually ending in .1 or .254 based on the scope size), is where your computer sends all its traffic to be routed onwards. For IPv6, more detailed information can be found in our article how-to-fix-ipv6-connectivity/. Additionally, on Mac or Linux systems, it can be verified using the following command:
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 172.16.235.190 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:a130:83e4:7198:bab%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): {222.253.102.42, 71.197.216.14}
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 22:e7:ba:f4:2b:e0
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 0d:92:21:40:0a:63
}
Resolving Issues with Wired and Wireless Connectivity
When it comes to transferring data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Users
Regardless of whether you are using OSX/macOS versions such as 10.12.9, 11.3.8, or 12.3.5, there are various troubleshooting tools available. However, the manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One invaluable tool for OSX/macOS users is the sudo wdutil info, which provides a dump of current wireless settings to the CLI 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 much of it relates to wireless settings and is only relevant at a specific point in time, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz, or to run it interactively using sudo /usr/bin/sysdiagnose and navigate to /var/tmp on Finder. However, be mindful of the file sizes, which can be around 300MB.
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