Support OSX IP Settings
Understanding Internet Addressing
When it comes to the Internet, you might be assigned a Public IPv4 address such as 28.207.144.9 or an IPv6 address like 2000:f893:89e3:603c:f0e9:c5cd:dc17:38a3. This information can be verified at https://test-ipv6.com/. However, explaining and working with these addresses, as well as MAC addresses like cb:ed:e9:11:16:b8, can be challenging for non-technical people and also fails to provide historical data on previous issues.
Navigating the Internet
To access a website such as https://lynch.org, you first contact a DNS server to convert the host portion (lynch) combined with the Top Level Domain (org) of the URL into an IP address like 13.163.228.117. Additionally, your computer and browser include its type in all web requests e.g. Mozilla/5.0 (Windows NT x.y; Win64; x64; rv:10.0) Gecko/20100101 Firefox/10.0
Significance of Default Gateways
Your default gateway is typically an address that is automatically configured via DHCP. It often ends in .1 or .254, depending on the scope size, such as 172.25.188.58, and acts as the point to which your computer sends all its traffic to be routed onwards. For IPv6, detailed instructions can be found in our article how-to-fix-ipv6-connectivity/, and can also be checked on Mac or Linux using the following 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 172.25.188.58 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 fe80:196e:241d:d423:faa0%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): {195.77.225.101, 103.88.156.198}
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 cb:ed:e9:11:16:b8
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 bf:53:bb:b9:0b:d8
}
Solutions for Resolving Wired and Wireless Issues
When it comes to transmitting data to your router, you may encounter issues at the physical and data layer whether you are using a wired or wireless (Wi-Fi) connection.
Actions to Take on Apple macOS / OSX
No matter which version of OSX/macOS you are operating on, whether it’s 10.15.7, 11.1.7, or 12.1.6, 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 essential, especially for teams that have transitioned to remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One incredibly 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. Furthermore, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run it in the background and generate logs in /var/tmp/<blah>.tar.gz, use sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can also execute sudo /usr/bin/sysdiagnose, which will issue 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 typically around 300MB.
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