How Can I Understand OSX Issues
How IP Addresses Function
When using the Internet, a user may be assigned a Public IPv4 address such as 74.34.225.245 or an IPv6 address such as 2000:650e:926d:3daa:6040:ee74:8e4f:36ee. Verification of these addresses is possible from https://test-ipv6.com/. Communicating these addresses, as well as MAC addresses like 58:4d:04:4f:c5:ac, can be complex and prone to errors for non-technical individuals. Moreover, this method does not provide access to historical data.
Navigating Websites
To visit a website like https://grimes-wolf.org, the first step is to contact a DNS server. This server translates the host section (grimes-wolf) and the Top Level Domain (org) of the URL into an IP address, like 214.31.162.96. When making web requests, your computer and browser also transmit the web request type, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. This gateway might look like 172.22.6.175 (although the final digits are usually .1 or .254, depending on the scope size), and it serves as the point to which your computer forwards all its traffic for further routing. For those interested in IPv6, we have provided comprehensive guidance on how-to-fix-ipv6-connectivity/. It is also possible to check this on Mac or Linux 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 172.22.6.175 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 fe80:277:c3f8:452d:fe1%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): {174.59.41.3, 138.15.44.193}
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 58:4d:04:4f:c5:ac
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 82:d4:78:ea:7a:bb
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may use either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of the version of OSX/macOS you are running, whether it’s 10.14.1, 11.5.9, or 12.1.1, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes especially useful, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Use of Pre-Built Scripts
An extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs that are mostly point-in-time only in relation to wireless, similar to wdutil.
To run sudo nohup /usr/bin/sysdiagnose -u & in the background and write logs to /var/tmp/<blah>.tar.gz. For an interactive run (although there is not much interaction), you can use sudo /usr/bin/sysdiagnose and it will give 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 specify the path. Be aware that the file sizes are approximately 300MB or so.
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