Troubleshoot Mac Connectivity

Understanding Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 222.186.12.33, or an IPv6 address like 2000:9580:40c7:5a25:c565:4f59:856a:ce48. Verification of these addresses can be done at https://test-ipv6.com/. However, for those unfamiliar with technology, communicating these addresses, including MAC addresses like 33:b6:ef:99:0a:cb, can be error-prone and complex. Understanding Internet Addressing When using the Internet, you are assigned a Public IPv4 address, such as 222.186.12.33, or an IPv6 address like 2000:9580:40c7:5a25:c565:4f59:856a:ce48. Verification of these addresses can be done at https://test-ipv6.com/. However, for those unfamiliar with technology, communicating these addresses, including MAC addresses like 33:b6:ef:99:0a:cb, can be error-prone and complex.

Understanding Internet Addressing

When using the Internet, you are assigned a Public IPv4 address, such as 222.186.12.33, or an IPv6 address like 2000:9580:40c7:5a25:c565:4f59:856a:ce48. Verification of these addresses can be done at https://test-ipv6.com/. However, for those unfamiliar with technology, communicating these addresses, including MAC addresses like 33:b6:ef:99:0a:cb, can be error-prone and complex. Moreover, this method lacks access to historical data, particularly when dealing with past issues.

In order to access a webpage such as https://fay.info, the process involves initially accessing a DNS server to translate the URL’s host portion (fay) combined with the Top Level Domain (info) into an IP address like 195.150.70.189. Whenever making web requests, your computer and browser also communicate their type, such as
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16

The Significance of Default Gateways

Usually, a default gateway is automatically configured through DHCP, providing an address like 172.28.109.12 (typically ending in .1 or .254 depending on the scope size). This is where your computer sends all its traffic to be routed onwards. For IPv6, a detailed guide can be found at how-to-fix-ipv6-connectivity/, with instructions for checking on Mac or Linux.

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  172.28.109.12    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   fe80:2aa9:aeb:fc1d:7304%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): {1.156.152.134, 232.67.223.128}
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 33:b6:ef:99:0a:cb
  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 96:c8:ad:ea:41:ae
}

Resolving Connectivity Issues in Wired and Wireless Networks

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

Effective Solutions for Apple macOS / OSX Users

Regardless of the version of OSX/macOS you are running - whether it’s 10.11.3, 11.3.7, or 12.1.2 - there are various troubleshooting tools available. However, manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that adopt remote work and Work From Anywhere (WFA) practices.

Useful Built-in Tools for Troubleshooting

One highly beneficial 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. Additionally, the sysdiagnose tool offers a more comprehensive option for generating various logs, although much of the information is only relevant to wireless at a specific point in time, similarly to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use 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. Just keep in mind that the file sizes are around 300MB or so.

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