How Can I DiagnOSe OSX IP Settings
How the System of Internet Addressing Operates
When using the Internet, you could be assigned a Public IPv4 address, such as 50.54.217.104, or an IPv6 address, such as 2000:2c2f:bf3e:e8bb:e3f6:cf38:f2e1:ead0. You can verify this at https://test-ipv6.com/. However, conveying these addresses, or even identifying MAC addresses like e8:e8:96:03:12:c4, can be prone to mistakes and quickly become complex, especially for individuals not well-versed in tech matters. In addition, this method lacks historical data, especially regarding past issues.
Navigating the Internet
To access a website like https://prohaska.com, you initially connect to a DNS server to translate the host portion (prohaska) along with the Top Level Domain (com) of the URL into an IP address, like 158.42.181.179. Whenever your computer and browser make web requests, they also transmit their specifications, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
Typically, your default gateway is an automatically assigned address through DHCP. This address, such as 172.31.103.127 (although they typically end in .1 or .254 depending on the scope size), is where your computer sends all its traffic to be subsequently routed. For troubleshooting IPv6 connectivity, we offer a comprehensive guide at how-to-fix-ipv6-connectivity/. Moreover, you can verify this on Mac or Linux with:
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 172.31.103.127 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:feb9:1ee:2c1:6079%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): {243.24.191.232, 221.86.56.30}
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 e8:e8:96:03:12:c4
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 11:ce:f2:bd:24:4c
}
Resolve Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple macOS / OSX
No matter which version of OSX/macOS you are using - whether it’s 10.13.8, 11.5.6, or 12.3.1 - there are various tools available for resolving issues. However, these manual actions and scripts do not provide a consistent series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that have adopted remote work and Work From Anywhere (WFA).
Useful Built-in Tools for Troubleshooting
On OSX/macOS, the sudo wdutil info command is a valuable tool that provides a dump of 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, although it primarily captures point-in-time data related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. For an interactive run (even though there is minimal interaction), you can execute 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, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to access the path. Keep in mind that the file sizes are approximately 300MB.
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