DiagnOSe MacOS IP Settings
Understanding Internet Addressing
When using the Internet, you are assigned a unique Public IPv4 address, such as 250.236.237.241, or an IPv6 address like 2000:151c:13a5:ac97:dfbd:5119:2e7e:5115. You can verify this by visiting https://test-ipv6.com/. However, for those not well-versed in technology, communicating these addresses or referencing MAC addresses like 4e:28:f9:bd:0e:ae can quickly become complicated and prone to errors. Moreover, this does not provide any historical data, especially from past incidents.
Navigating the Internet and the Process of Lookups
When you want to access a website like https://mueller.net, your first step is to contact a DNS server to convert the host part (mueller) combined with the Top Level Domain (net) of the URL into an IP address, such as 227.155.118.121. Every time your computer and browser request a web page, they also submit their 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
Your default gateway is typically an automatically assigned address through DHCP. You may receive a default gateway like 10.190.62.60 (usually ending in .1 or .254, depending on the scope size), which is where your computer sends all its traffic to be further routed. For extensive information on IPv6 connectivity, read our in-depth guide: how-to-fix-ipv6-connectivity/. Alternatively, you can check 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 10.190.62.60 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 fe80:57ad:e119:8242:fdb0%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): {95.46.238.31, 235.251.198.157}
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 4e:28:f9:bd:0e:ae
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 a3:29:0f:3e:f3:aa
}
Fixing Network Connectivity Issues
When it comes to transmitting data to your router, you might be using either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting on Apple Operating Systems
No matter which version of OSX/macOS you’re using - whether it’s 10.15.3, 11.3.6, or 12.2.8 - there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that embrace remote work and Work From Anywhere (WFA).
Effective Built-in Scripts and Commands
A very useful tool on OSX/macOS is sudo wdutil info, which provides a dump of current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting. Another comprehensive tool is the sysdiagnose tool, which can generate a wide range of logs (although mostly point-in-time related to wireless, just like wdutil).
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there isn’t much interaction), you can runsudo /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 using Finder with Cmd+Shift+G. Just be cautious of the file sizes, which are around 300MB more or less.
Useful Videos
P.S. Tips For Remote Network and Client Support
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