How Do You Troubleshoot Mac Issues
Understanding Internet Addressing
When using the Internet, your device may have a unique Public IPv4 address, such as 166.174.81.251, or an IPv6 address, like 2000:4ec3:ea67:9dbd:e9bd:91b5:9a4f:c2c3. This information can be verified using https://test-ipv6.com/, but explaining these addresses to non-technical individuals or referencing MAC addresses like 7e:07:37:aa:b6:e0 can be error-prone and complex. Furthermore, this data does not provide historical context, especially when considering past issues.
Navigating the World Wide Web
Accessing a webpage, such as https://conroy-grimes.com, involves the use of a DNS server to convert the host portion (conroy-grimes) combined with the Top Level Domain (com) of the URL to an IP address, such as 228.201.11.39. Additionally, your computer and browser transmits its type with every web request, as seen here:
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
The default gateway is typically an automatically configured address obtained through DHCP, such as 172.16.8.222 (commonly ending in .1 or .254 based on the scope size). This address is where your computer directs all of its traffic for routing. For those interested in IPv6, a detailed guide on how-to-fix-ipv6-connectivity/ is available, and users of Mac or Linux can check as follows:
Command to check default gateway on Mac or Linux
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 172.16.8.222 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:cd3b:ad88:c4e4:3eb4%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): {205.161.157.105, 187.32.35.53}
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 7e:07:37:aa:b6:e0
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 18:15:2d:bc:c6:bb
}
Solutions for Dealing with Wired or Wireless 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.
Tips for Resolving Issues on Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.15.7, 11.5.8, or 12.2.9, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a consistent set of correlated values over time. This is where automated remote troubleshooting becomes crucial, particularly for teams that have adopted remote work and Work From Anywhere (WFA).
Pre-Installed Scripts That Offer Assistance
A helpful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of the information is only relevant to the wireless issue, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use the command sudo /usr/bin/sysdiagnose and it will display a privacy warning. When 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 locate the path. Keep in mind that the file sizes are about 300MB, more or less.
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