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Explanation of Internet Addressing
When using the Internet, one may have a public IPv4 address, represented by something like 7.21.182.222, or an IPv6 address, such as 2000:c717:b9e0:d426:68ba:d6b3:66ec:d456. It is possible to verify this by visiting https://test-ipv6.com/. However, for those who are not well-versed in technology, conveying these addresses or even mentioning MAC addresses like 82:20:67:90:33:d1 can be problematic and become complex very quickly. Moreover, this method does not provide any historical data, particularly regarding past issues.
Navigating the World Wide Web
In order to reach a website, such as https://ferry-von.biz, the initial step is to access a DNS server, which will translate the host portion (in this case, “ferry-von”) combined with the Top Level Domain (“biz”) of the URL to an IP address, like 209.40.142.159. Your computer and browser actually send information about their type with every web request, as seen in the following 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
Significance of Default Gateways
By default, your gateway is an automatically configured address through DHCP. For instance, one may receive a default gateway like 192.168.17.154 (although they typically end in .1 or .254 depending on the scope size), and this is where one’s computer sends all its traffic to be routed onwards. For IPv6, a detailed explanation can be found by visiting how-to-fix-ipv6-connectivity/. On Mac or Linux, this can be checked with:
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 192.168.17.154 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 fe80:61e2:5eec:3e59:5e1%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): {52.157.225.218, 29.235.151.206}
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 82:20:67:90:33:d1
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 1a:dc:a6:0b:17:99
}
Resolving Connectivity Issues with Wired and Wireless Networks
When transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Troubleshooting
Irrespective of the version of OSX/macOS you are using - be it 10.14.6, 11.2.8, or 12.1.9 - there are various tools available for troubleshooting. Unfortunately, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting proves to be extremely beneficial, especially for teams that are embracing remote work and the concept of Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One incredibly useful tool for OSX/macOS is the sudo wdutil info, which provides a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although many relate to wireless settings at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose, which will result in 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 Finder with Cmd+Shift+G. However, be cautious of the file sizes, which are approximately 300MB.
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