How To DiagnOSe OSX IP Settings

Understanding the Allocation of Internet Addresses

When connecting to the Internet, you are assigned a Public IPv4 address, such as 41.241.70.48, or an IPv6 address, such as 2000:a7a4:db86:c4cf:fd0b:fc69:f9c4:e4a8. These addresses can be verified at https://test-ipv6.com/. However, for individuals without technical expertise, communicating these addresses, or even referencing MAC addresses like fd:3e:f1:d1:32:03, can be prone to errors and become complex very quickly. Moreover, this method does not provide any historical data, especially regarding past issues.

Navigating the Internet

When accessing a website such as https://goodwin.co, you must first contact a DNS server to translate the host portion (goodwin) combined with the Top Level Domain (co) of the URL into an IP address, such as 41.197.219.253. Notably, your computer and browser transmit its type with all web requests, for example:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A

The Significance of Default Gateways

Typically, your default gateway is an automatically configured address through DHCP. You receive a default gateway like 192.0.0.52 (although they often end in .1 or .254 depending on the scope size) and this is the destination where your computer directs all its traffic to be routed further. For IPv6, detailed instructions are available in our article how-to-fix-ipv6-connectivity/, but you can verify 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  192.0.0.52    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   fe80:5d9d:b06d:b7f2:ceb0%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): {62.174.215.245, 172.43.209.64}
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 fd:3e:f1:d1:32:03
  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 8b:b8:69:43:33:4d
}

Fixing Connection Issues in Wired or Wireless Networks

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

Regardless of whether you are running OSX/macOS version 10.12.9, 11.3.3, or 12.2.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes particularly useful, especially for teams embracing remote work and Work From Anywhere (WFA).

Useful Built-in Scripts for Troubleshooting

One useful tool on OSX/macOS is “sudo wdutil info,” which provides a current wireless settings dump to the command-line interface 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 much of it is point-in-time information related to wireless, similar to wdutil.

To run the sysdiagnose tool in the background and write logs to “/var/tmp/.tar.gz,” use the command “sudo nohup /usr/bin/sysdiagnose -u &”. For an interactive (though minimal interaction) experience, you can run “sudo /usr/bin/sysdiagnose,” which will provide 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 point Finder to the path. However, be cautious of the file sizes, which are approximately 300MB.

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