How To Support MacOS Issues
Understanding Internet Protocol Addresses
When using the Internet, you are typically assigned a Public IPv4 address, for example like this: 188.137.51.49 or an IPv6 address such as 2000:b179:a1e4:f030:9ef6:81b6:df7a:8083. You can verify these addresses using the website https://test-ipv6.com/. However, for those who are not very technically inclined, communicating these addresses, or even mentioning MAC addresses like 17:bc:27:3d:4f:d6, can be prone to errors and become confusing. Furthermore, this method does not provide any historical data, especially when dealing with past issues.
Navigating the World Wide Web
To access a website like https://moen.biz, your device first needs to contact a DNS server to translate the host name (moen) combined with the Top Level Domain (biz) of the URL, into an IP address, such as 169.12.52.27. Your computer and web browser actually include its type with 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
The Significance of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP, such as 192.168.37.89 (although they typically end in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, a thorough guide is available on how-to-fix-ipv6-connectivity/ but you can also check on a Mac or Linux system using the following command:
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 192.168.37.89 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 fe80:1214:608c:1232:f39b%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): {76.132.52.89, 88.223.209.24}
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 17:bc:27:3d:4f:d6
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 37:7f:3f:e4:3f:08
}
Resolving Connectivity Issues on Wired or Wireless Networks
When it comes to sending 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 whether you are running OSX/macOS versions such as 10.15.6, 11.3.3, or 12.2.8, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes crucial, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Useful Built-in Scripts
An extremely helpful tool on OSX/macOS is the sudo wdutil info command, which displays the current wireless related settings in the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only point-in-time data in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be aware that the file size is around 300MB or less.
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