How Do You Fix OSX IP Settings
Understanding Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 or IPv6 address. These addresses can be verified using a tool like https://test-ipv6.com/. However, relaying these addresses to non-technical individuals can be error-prone and complex. Furthermore, this method lacks the capability to provide historical data related to previous issues.
Navigating the World Wide Web
Accessing a website such as https://cruickshank.name involves contacting a DNS server to convert the host (cruickshank) and Top Level Domain (name) of the URL into an IP address, such as 181.158.71.61. Additionally, your computer and web browser transmit its specifications with each web request, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
Significance of Default Gateways
The default gateway is typically an automatically assigned address via DHCP. It serves as the destination for all outbound traffic from your computer. For IPv6, a detailed explanation can be found at how-to-fix-ipv6-connectivity/. Moreover, on Mac or Linux, the default gateway can be verified 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 192.168.61.149 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 fe80:3ee0:6f3e:6845:500f%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): {114.19.54.72, 86.99.203.240}
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 a6:13:4c:cd:2e:90
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 74:d6:59:c4:9f:30
}
Fixing Issues with Wired and Wireless Connectivity
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 Tips for Apple macOS / OSX
Regardless of whether you’re running OSX/macOS version 10.15.7, 11.3.6, or 12.0.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, particularly for teams that have embraced remote work and Work From Anywhere (WFA).
Useful Built-in Scripts
One useful tool for OSX/macOS is sudo wdutil info, which provides a dump to the CLI of current wireless settings and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although they are mostly point-in-time in relation to wireless, similar to wdutil.
To run it in the background and generate logs, use the command sudo nohup /usr/bin/sysdiagnose -u &, which will write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose with caution regarding privacy warnings. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp using Finder or the path /var/tmp with Cmd+Shift+G. Keep in mind that the file sizes are around 300MB, more or less.
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