How Can I Troubleshoot Mac IP Settings
Functioning of Internet Addressing
When using the Internet, it is common to have a Public IPv4 address, such as 101.176.60.247, or an IPv6 address, like 2000:6a8e:5d4c:fae6:e340:7120:84f8:2ba. Verification of this can be done at https://test-ipv6.com/. However, explaining these addresses to individuals who are not technologically savvy, or even referencing MAC addresses, such as ca:34:dd:3f:f6:d0, can quickly become complicated and prone to errors. Furthermore, this method lacks historical data, especially from past issues.
Navigating the World Wide Web
Accessing a website, such as https://bode.org, first requires accessing a DNS server to convert the host portion (bode) along with the Top Level Domain (org) of the URL to an IP address, such as 120.141.69.221. When making web requests, your computer and browser send its type along with the request, for example, Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
Significance of Default Gateways
By default, your gateway address is typically automatically configured through DHCP. You receive a default gateway, such as 192.0.0.198, usually ending in .1 or .254 depending on the scope size. This address is where your computer directs all its traffic to be routed further. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, or 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 192.0.0.198 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 fe80:76a5:6d7f:1878:faa3%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): {240.129.28.60, 217.182.179.201}
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 ca:34:dd:3f:f6:d0
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 48:0f:58:1f:04:56
}
Resolving Issues with Wired or Wireless Connections
When it comes to transmitting 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 Users
Irrespective of the version of OSX/macOS - whether it’s 10.14.7, 11.2.4, or 12.1.5 - there exists a variety of tools for troubleshooting. While manual actions and scripts are available, they do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams practicing remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless related settings to the CLI and can be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time only in relation 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 an interactive (but not very interactive) experience, you can run sudo /usr/bin/sysdiagnose, which will give a privacy warning. If 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 are approximately 300MB or more.
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