How Do You Troubleshoot OSX IP Settings

Understanding the Functionality of Internet Addressing When using the Internet, it’s common to have either a Public IPv4 address, such as 149.31.11.139, or an IPv6 address, such as 2000:c0bd:70b2:cc7c:57d7:3a22:dee1:8215. Verification of this information can be done through https://test-ipv6. Understanding the Functionality of Internet Addressing When using the Internet, it’s common to have either a Public IPv4 address, such as 149.31.11.139, or an IPv6 address, such as 2000:c0bd:70b2:cc7c:57d7:3a22:dee1:8215. Verification of this information can be done through https://test-ipv6.

Understanding the Functionality of Internet Addressing

When using the Internet, it’s common to have either a Public IPv4 address, such as 149.31.11.139, or an IPv6 address, such as 2000:c0bd:70b2:cc7c:57d7:3a22:dee1:8215. Verification of this information can be done through https://test-ipv6.com/. Communicating these addresses, or MAC addresses like 71:93:47:e1:a4:c9, can be complex and susceptible to errors, particularly for those with limited technical knowledge. Furthermore, historical data is not available when addressing past issues.

In order to access a website like https://crooks.net, you make an initial connection to a DNS server to convert the host portion (crooks) combined with the Top Level Domain (net) of the URL into an IP address, such as 227.135.151.1. Your computer and browser specifies its type with all web requests, for example:
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko

Understanding the Significance of Default Gateways

By default, your gateway is an address that is usually automatically configured via DHCP. A default gateway, such as 192.0.0.59 (typically ending in .1 or .254 depending on the scope size), is where your computer sends all of its traffic to be routed onwards. For IPv6, you can refer to our in-depth guide on how-to-fix-ipv6-connectivity/ or utilize Mac or Linux to check.

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  192.0.0.59    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:d6a7:f189:e31a:72c1%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): {132.79.4.249, 175.70.94.238}
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 71:93:47:e1:a4:c9
  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 79:41:e5:59:92:57
}

How to Resolve 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.

Solutions for Apple macOS / OSX Users

Regardless of your version of OSX/macOS - whether it’s 10.13.4, 11.0.6, or 12.0.2 - 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, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.

Effective Built-in Scripts for Troubleshooting

One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI, and this 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 only relevant to wireless at a specific point in time, similar to wdutil.

By running sudo nohup /usr/bin/sysdiagnose -u & in the background, logs will be written to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will display 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 Cmd+Shift+G in Finder. However, be mindful of the file sizes, which are typically around 300MB.

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