DiagnOSe Apple Connectivity
Understanding Internet Addressing Systems
When using the Internet, you are assigned a unique Public IPv4 or IPv6 address. The former may look like 39.29.76.101, while the latter is in the form of 2000:c55d:d910:a981:cba9:3bea:2486:18e4. You can verify your IP address by visiting https://test-ipv6.com/. However, for those not well-versed in technology, conveying these addresses, or even MAC addresses like 86:e9:40:b1:7b:61, can be prone to errors and become complex quickly. Moreover, this method lacks historical data, especially when troubleshooting past issues.
The Process of Reaching Websites
When you want to access a webpage, such as https://ullrich.io, your computer first contacts a DNS server to translate the URL’s host portion (ullrich) and its Top Level Domain (io) into an IP address, such as 101.255.254.211. In addition, your computer and browser include its type in all web requests, for instance:
Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Significance of Default Gateways
By default, your gateway address is typically assigned through DHCP and may appear as 192.0.0.113 (although they usually end in .1 or .254 based on the scope size). This gateway serves as the destination to which your computer forwards all its traffic. To troubleshoot IPv6 connectivity on Mac or Linux, refer to how-to-fix-ipv6-connectivity/.
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 192.0.0.113 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 fe80:84e8:a19a:2baf:9afb%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): {252.20.186.10, 249.11.216.26}
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 86:e9:40:b1:7b:61
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 a0:d9:67:b9:38:5b
}
Resolving Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layers.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.15.2, 11.1.1, or 12.3.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that are embracing remote work and the Work From Anywhere (WFA) model.
Utilizing Built-in Scripts for Assistance
On OSX/macOS, the sudo wdutil info tool is extremely useful as it provides a dump of the current wireless-related settings to the CLI, and it can also be configured to generate specific logs for troubleshooting purposes. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of the information is only relevant to a specific point in time with regards to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in the /var/tmp/<blah>.tar.gz directory. For an interactive mode (although there is minimal interaction), runsudo /usr/bin/sysdiagnose and it will issue a privacy warning. If not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to access the path. Keep in mind that the file sizes are approximately 300MB.
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