How To Fix Mac Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address or an IPv6 address. The Public IPv4 address could be numbers like 138.13.235.238, while an IPv6 address may look like 2000:4330:c1ef:8921:f08a:b4b0:c0f8:c469. You can verify your address at https://test-ipv6.com/. However, for those not well-versed in technology, conveying these addresses, or even recalling MAC addresses like 90:8d:ec:ef:9e:5c, can be prone to errors and quickly become complicated. Furthermore, this method does not provide any historical data, especially during previous technical issues.
Navigating the World Wide Web
When attempting to access a website, such as https://hettinger.co, the initial step is to reach a DNS server to convert the combination of the host portion (hettinger) and the Top Level Domain (co) of the URL into an IP address, such as 121.163.225.106. In all web requests, your computer and browser send their type as well, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A
Understanding the Significance of Default Gateways
Typically, your default gateway is an automatically configured address through DHCP. This default gateway, such as 192.0.0.44 (although they usually end in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed onwards. For IPv6, detailed information can be found in how-to-fix-ipv6-connectivity/. On Mac or Linux, you can verify this through:
ifconfig
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 192.0.0.44 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:c23e:49:9d9a:e326%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): {141.224.74.46, 13.193.76.82}
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 90:8d:ec:ef:9e:5c
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 9e:49:a2:e3:f8:b6
}
Troubleshooting Network Issues - Wired vs. Wireless
When it comes to transferring data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Solutions for Apple macOS / OSX Users
No matter which version of OSX/macOS you’re using, whether it’s 10.12.4, 11.2.1, or 12.2.7, 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, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Built-in Tools
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump to the CLI of current wireless settings and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs related to wireless, although much of it is point-in-time data similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose and it will provide 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 be aware that the file sizes are approximately 300MB.
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