How Do You Test OSX IP Settings
Functioning of Internet Addressing
When using the Internet, it is common to receive either a Public IPv4 address, such as 109.199.132.189, or an IPv6 address like 2000:f688:c12f:e879:571b:ceb9:783b:f66e. The authenticity of these addresses can be verified at https://test-ipv6.com/. However, these addresses are complex and prone to error, especially when communicated to individuals who are not technically inclined. Additionally, these addresses do not provide historical data, particularly from past occurrences of problems.
Navigating the Internet
Accessing a webpage, such as https://schowalter-ortiz.io, involves initial interaction with a DNS server to translate the combined host portion (schowalter-ortiz) and the Top Level Domain (io) of the URL into an IP address, such as 169.106.153.37. Whenever a web request is made, both the computer and browser send their type information, for example: 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 usually an automatically configured address through DHCP. It typically appears as a default gateway, such as 172.29.244.165, (ending in .1 or .254 based on the scope size), where computers direct all their traffic for routing. For IPv6, detailed guidance on how-to-fix-ipv6-connectivity/ is available, and a similar check can be performed on Mac or Linux using:
<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 172.29.244.165 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 fe80:9f27:38fd:9572:9822%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): {253.170.145.11, 232.194.58.84}
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 da:bd:76:90:d9:b6
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 d6:03:11:2b:83:88
}
Resolving Issues with Wired and Wireless Connections
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of which version of OSX/macOS you are operating on, whether it’s 10.12.9, 11.3.6, or 12.0.4, there are various troubleshooting tools available. However, the manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams engaged in remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts
A useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI, and can be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although they are mostly point-in-time only in relation to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive run, use the command sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. Upon completion, 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 file sizes are approximately 300MB.
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