Understand Mac Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 231.136.35.90 or an IPv6 address like 2000:4053:76de:e105:c3bc:78ef:eb17:bb5c. You can verify this information at https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even referencing MAC addresses such as c6:a9:99:fe:42:ac, can be prone to errors and become complex. Moreover, it does not provide any historical data.
Navigating the World Wide Web
When attempting to access a website like https://hoeger-powlowski.org, you start by contacting a DNS server to convert the host portion (hoeger-powlowski) and the Top Level Domain (org) of the URL into an IP address, such as 63.194.153.45. Your computer and browser include its type in all web requests, 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
Significance of Default Gateways
The default gateway is usually an automatically configured address obtained via DHCP. It typically ends in .1 or .254 based on the scope size, and your computer sends all its traffic to this address to be routed onwards. For IPv6, a detailed explanation is available at how-to-fix-ipv6-connectivity/. On Mac or Linux, you can check this through:
code block
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 172.18.73.90 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:b04e:db8a:2b6c:4a2%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): {193.135.23.53, 220.13.121.136}
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 c6:a9:99:fe:42:ac
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 20:a7:f9:50:40:6f
}
Resolve Connection Issues for Wired or Wireless Networks
When it comes to transmitting data to your router, you could be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Resolving Problems on Apple macOS / OSX
No matter which version of OSX/macOS you have - whether it’s 10.14.8, 11.2.6, or 12.2.5 - there are various tools available for troubleshooting. However, these manual actions and scripts fail to provide a consistent set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts to Aid in Troubleshooting
A helpful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs, although much of it is only relevant to wireless issues, much like the wdutil tool.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. Alternatively, running it interactively by using sudo /usr/bin/sysdiagnose will prompt 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 Finder by pressing Cmd+Shift+G. However, be cautious of the large file sizes, which are typically around 300MB.
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