How Do You Check Mac Connectivity
Understanding Internet Addressing
When using the Internet, you may be assigned a Public IPv4 address, such as 148.85.118.171, or an IPv6 address, like 2000:b502:64bc:b8fa:bbb2:1a95:217c:c7f9. You can verify this using https://test-ipv6.com/. However, for individuals without technical expertise, attempting to communicate these addresses, or even identifying MAC addresses like 12:d9:d3:8e:30:a2, can lead to errors and quickly become complex. Furthermore, this does not provide any historical data, particularly from past issues.
Navigating the World Wide Web
When trying to access a webpage, such as https://nicolas.net, your first step is to access a DNS server to convert the host part (nicolas) combined with the Top Level Domain (net) of the URL to an IP address, like 227.127.187.102. Every web request from your computer and browser includes its type, such as Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
Typically, your default gateway is an automatically assigned address via DHCP. You might receive a default gateway, such as 172.26.16.250 (usually ending in .1 or .254 depending on the scope size), which is where your computer sends all its traffic to be routed onwards. For IPv6, you can explore further in how-to-fix-ipv6-connectivity/ or check on Mac or Linux with:
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 172.26.16.250 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 fe80:2359:a120:16bb:2e4e%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): {251.57.237.151, 49.60.209.217}
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 12:d9:d3:8e:30:a2
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 00:45:4e:61:12:4e
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Trouble-shooting Strategies for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.12.3, 11.1.2, or 12.0.2, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One extremely useful tool on OSX/macOS 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. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is related to wireless settings and is only relevant to a specific point in time similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz. Alternatively, running sudo /usr/bin/sysdiagnose interactively (although there is limited interaction) will prompt a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G or search for the path. Keep in mind that the file sizes are approximately 300MB or more.
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