How Do You DiagnOSe Mac Issues

Understanding How Internet Addressing Functions When using the Internet, individuals may be assigned a Public IPv4 address, such as 212.124.27.152, or an IPv6 address, like 2000:ee4:1563:fac8:8a37:32a6:f6f9:263b. To verify this, visit https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like c6:4d:34:d4:ec:e4, can be error-prone and complex for those who are not tech-savvy. Understanding How Internet Addressing Functions When using the Internet, individuals may be assigned a Public IPv4 address, such as 212.124.27.152, or an IPv6 address, like 2000:ee4:1563:fac8:8a37:32a6:f6f9:263b. To verify this, visit https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like c6:4d:34:d4:ec:e4, can be error-prone and complex for those who are not tech-savvy.

Understanding How Internet Addressing Functions

When using the Internet, individuals may be assigned a Public IPv4 address, such as 212.124.27.152, or an IPv6 address, like 2000:ee4:1563:fac8:8a37:32a6:f6f9:263b. To verify this, visit https://test-ipv6.com/. However, conveying these addresses, as well as MAC addresses like c6:4d:34:d4:ec:e4, can be error-prone and complex for those who are not tech-savvy. Moreover, it does not provide historical data, especially regarding past issues.

When attempting to access a webpage, such as https://witting.org, the first step is to access a DNS server to convert the host portion (witting) and the Top Level Domain (org) of the URL into an IP address, such as 118.159.242.110. Each web request from your computer and browser also includes its type, 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

In most cases, the default gateway is an address that is automatically configured via DHCP. This default gateway, such as 10.34.31.237 (usually ending in .1 or .254 based on the scope size), is where a computer sends all its traffic to be routed further. For a detailed guide on configuring it for IPv6, refer to how-to-fix-ipv6-connectivity/, or check it on Mac or Linux 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  10.34.31.237    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   fe80:4d2a:8401:9189:e8bf%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): {137.178.221.146, 216.177.128.48}
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 c6:4d:34:d4:ec:e4
  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 e1:56:71:02:9f:38
}

Resolving Issues with Wired and Wireless Connectivity

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 layer.

Troubleshooting Tips for Apple’s macOS / OSX

Regardless of which version of OSX/macOS you are using, whether it’s 10.11.8, 11.6.4, or 12.1.5, there are several tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that practice remote work and Work From Anywhere (WFA).

Utilizing Built-in Scripts for Assistance

On OSX/macOS, a useful tool is sudo wdutil info, which dumps current wireless related settings to the CLI and can also generate specific logs for troubleshooting. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to the wireless issues, similar to wdutil.

To run sudo nohup /usr/bin/sysdiagnose -u & in the background and have it write logs to /var/tmp/<blah>.tar.gz. For an interactive option (even though there is minimal interaction), you can run sudo /usr/bin/sysdiagnose and it will prompt a privacy warning. If not run in the background, it should open Finder in the correct location. Otherwise, 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 around 300MB more or less.

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