How To Understand OSX IP Settings
The Functioning of Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 171.207.23.21 or an IPv6 address such as 2000:f847:5cc0:1d1e:68c1:4dc1:cca2:795. You can verify this information at https://test-ipv6.com/. However, for individuals who are not well-versed in technology, conveying these addresses or even mentioning MAC addresses like 6f:36:5a:51:3f:1f can quickly become complex and prone to error. Furthermore, this method does not provide any historical data, especially regarding previous issues.
Navigating the World Wide Web
When wanting to access a website such as https://bechtelar.com, the first step is to contact a DNS server to convert the host portion (bechtelar) along with the Top Level Domain (com) of the URL to an IP address like 196.210.1.77. Every web request sent by your computer and browser includes its type, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway is usually an address that is automatically configured through DHCP. Typically, you would receive a default gateway such as 192.0.0.142 (although they typically end in .1 or .254 depending on the scope size), and this is where your computer directs all of its traffic to be routed further. For a detailed analysis of IPv6, you can refer to how-to-fix-ipv6-connectivity/. You can also verify this 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 192.0.0.142 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:c297:6c17:1736:c5eb%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): {42.95.184.252, 110.64.74.168}
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 6f:36:5a:51:3f:1f
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 16:c4:e0:ac:4a:ab
}
Fixing Connectivity Issues on Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Addressing Problems on Apple’s Operating Systems
No matter which version of the macOS/OSX you are using, whether it’s 10.11.1, 11.1.4, or 12.0.6, there is a variety of troubleshooting tools available. However, they may fall short in providing a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for remote work and Work From Anywhere (WFA) teams.
Leveraging Built-in Tools for Support
A useful tool on OSX/macOS is the sudo wdutil info command, which provides current wireless settings dump to the CLI, and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool offers a comprehensive way to generate a wide range of logs, though much is only relevant to wireless settings at a specific point in time, similar to wdutil.
To run sysdiagnose in the background and have it write logs to /var/tmp/<blah>.tar.gz, use the command: sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, use: sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G. Keep in mind that the file sizes can be around 300MB.
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