How To Troubleshoot Apple Connectivity

Understanding How Internet Addressing Functions

When accessing the internet, you might come across a Public IPv4 address such as 213.233.27.170 or an IPv6 address like 2000:fbe1:dc29:9f07:cdff:a7e1:b278:74a8. You can verify this information by visiting https://test-ipv6.com/. However, for individuals who are not well-versed in technology, relaying and using these addresses, or even referencing MAC addresses like 36:11:df:e8:c6:99, can lead to errors and complications. Moreover, it does not provide any historical data, particularly when past issues have arisen.

Navigating the World Wide Web

In order to access a website, such as https://gulgowski.info, the first step is to connect to a DNS server to convert the host portion (gulgowski) in combination with the Top Level Domain (info) of the URL into an IP address, such as 16.198.199.137. Each time you make a web request, your computer and browser sends its specifications, 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

The Significance of Default Gateways

Your default gateway is typically an address that is automatically configured through DHCP. It is a crucial component, such as 172.27.201.81 (usually ending in .1 or .254 based on the scope size), to which your computer directs all of its traffic for further routing. For IPv6, a comprehensive guide on how-to-fix-ipv6-connectivity/ is available. On Mac or Linux systems, you can check this by 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  172.27.201.81    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   fe80:1d2b:86da:e47:8c7c%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): {21.60.75.150, 214.203.106.53}
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 36:11:df:e8:c6:99
  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 63:f0:c0:90:bb:ce
}

Troubleshooting Connectivity Issues

When it comes to transferring data to your router, you may encounter problems either with a wired or wireless (Wi-Fi) connection at the physical and data layer.

Resolving Connectivity Problems on Apple Devices

Regardless of the version of OSX or macOS you are using, whether it’s “10.13.5”, “11.4.7”, or “12.0.1”, there are various tools available for troubleshooting. However, these tools do not provide a set of correlated values over time, making it difficult to identify patterns. This is where remote troubleshooting becomes valuable, particularly for teams that embrace remote work and the Work From Anywhere (WFA) concept.

Utilizing Pre-installed Scripts for Assistance

One of the most useful tools on OSX/macOS is the “sudo wdutil info” command, which allows for the extraction of current wireless settings in the Command Line Interface (CLI) and the generation of specific troubleshooting logs. Moreover, the “sysdiagnose” tool can be used to produce a wide array of logs, although many are only relevant to wireless issues, similar to wdutil.

Running “sudo nohup /usr/bin/sysdiagnose -u &” in the background will generate logs in “/var/tmp/.tar.gz”. Alternatively, you can run “sudo /usr/bin/sysdiagnose” interactively, which will trigger a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to “/var/tmp” using Finder or Cmd+Shift+G. Keep in mind that the file sizes can be around 300MB, more or less.

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