How Do You Fix MacOS Issues
Understanding Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 address, such as 251.68.22.145, or an IPv6 address like 2000:7eee:b703:fc30:f7fe:b88f:da8f:96b1. You can verify this information by visiting https://test-ipv6.com/. However, conveying or referencing these addresses, including MAC addresses like 4a:76:43:a6:da:f0, can be complicated and error-prone, especially for those who are not tech-savvy. Furthermore, this method does not provide any historical data, particularly when dealing with past issues.
Navigating the World Wide Web
To access a website, such as https://pfeffer.info, you first contact a DNS server to convert the host portion (pfeffer) combined with the Top Level Domain (info) of the URL into an IP address, like 241.128.120.198. Your computer and browser transmit their 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. This address, such as 172.24.142.143 (usually ending in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be routed onward. For IPv6, detailed instructions can be found in our article how-to-fix-ipv6-connectivity/, but you can also check on Mac or Linux 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 172.24.142.143 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 fe80:663c:20c9:e6b1:4219%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): {230.118.66.173, 95.25.17.112}
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 4a:76:43:a6:da:f0
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 67:17:20:bd:95:ab
}
Addressing Wired and Wireless Connectivity Issues
When it comes to transmitting data to your router, you may be utilizing a wired connection or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Techniques for Apple macOS / OSX
Regardless of whether you are using OSX/macOS version 10.11.5, 11.1.3, or 12.2.9, there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, making remote troubleshooting particularly valuable for remote work and Work From Anywhere (WFA) teams.
Utilizing Built-in Scripts for Assistance
One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can generate a wide range of logs, although much of it is point-in-time data related to wireless, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for an interactive (although minimal interaction) experience, you can run sudo /usr/bin/sysdiagnose, which will prompt a privacy warning and provide the logs. Be cautious of the file sizes, which are around 300MB.
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