How Can I Understand OSX Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 178.224.54.94, or an IPv6 address, like 2000:c7ea:4ea9:f6ca:294:ae92:5632:6e02. You can verify this information on https://test-ipv6.com/. However, conveying these addresses to individuals who are not technically inclined, as well as mentioning MAC addresses like 24:b0:a0:f8:90:5c, can be prone to errors and become complex. Moreover, it does not provide historical data, especially from prior issues.
Navigating the Internet
When attempting to access a webpage, such as https://herman.net, you first contact a DNS server to convert the host (herman) and the Top Level Domain (net) of the URL into an IP address, like 40.245.67.225. Your computer and browser include specific details with every web request, such as Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
The default gateway is typically an address automatically configured via DHCP. You are assigned a default gateway, such as 192.168.111.136 (usually ending in .1 or .254 depending on the scope size), to which your computer sends all its traffic to be routed. For IPv6, a detailed analysis can be found at how-to-fix-ipv6-connectivity/, and on Mac or Linux, it can be verified using:
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 192.168.111.136 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 fe80:30c3:2db9:16e9:e914%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): {177.27.76.184, 73.122.162.197}
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 24:b0:a0:f8:90:5c
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 59:19:e3:49:7b:bb
}
Solutions for Wired and Wireless Connection Issues
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Steps to Resolve Problems on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.13.6, 11.2.4, or 12.0.9, there are various troubleshooting tools available. However, these manual actions and scripts lack the ability to provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Effective Built-in Tools for Troubleshooting
One useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings in the CLI, and can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can executesudo /usr/bin/sysdiagnose, which will prompt a privacy warning. If not run in the background, the logs should open in Finder at the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. However, be cautious of the file sizes, which can be around 300MB or more.
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