How Do You Troubleshoot Mac Internet Connection

Understanding Internet Addressing

When connecting to the Internet, you are assigned either a Public IPv4 address, such as 162.227.148.120, or an IPv6 address, like 2000:8ccb:1686:f429:ea3d:dfbd:308f:9156. You can verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or even mentioning MAC addresses like 3c:4c:fc:e3:fc:c8, can be prone to errors and becomes complex very quickly. Moreover, this method does not provide any historical data, especially regarding past issues.

Navigating the World Wide Web

When accessing a website, such as https://marquardt-schaefer.info, you first connect to a DNS server to convert the host portion (marquardt-schaefer) along with the Top Level Domain (info) of the URL into an IP address, such as 119.230.43.10. Every web request initiated by your computer and browser includes its type, for example
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko

Significance of Default Gateways

Your default gateway is typically an automatically assigned address via DHCP. The default gateway, such as 172.30.167.155 (commonly ending in .1 or .254 based on the scope size), is where your computer directs all its traffic to be forwarded. For IPv6, detailed instructions can be found at how-to-fix-ipv6-connectivity/, but you can also check 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  172.30.167.155    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   fe80:52c0:bc4e:aeb6:4950%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): {0.111.192.212, 106.106.237.51}
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 3c:4c:fc:e3:fc:c8
  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 22:b7:ec:f0:22:0b
}

Resolve Issues with Wired and Wireless Connections

When sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.

How to Address Problems on Apple macOS / OSX

No matter which version of OSX/macOS you are currently using - whether it’s 10.12.7, 11.1.3, or 12.2.2 - 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 essential, particularly for teams that are embracing remote work and the Work From Anywhere (WFA) concept.

Pre-existing Scripts That Can Provide Assistance

One useful tool on OSX/macOS is the sudo wdutil info, which provides a dump to the CLI of current wireless settings. 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 settings, similar to wdutil.

To run it in the background and write logs to /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively (even though there isn’t much interaction), you can use sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When 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. Keep in mind that the file sizes are approximately 300MB.

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