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Understanding the Functioning of Internet Addressing

When using the Internet, individuals receive distinct IP addresses, such as a Public IPv4 address like 15.179.213.3 or an IPv6 address like 2000:1248:a100:d33d:f012:64ba:8e2d:2f02. This information can be verified on https://test-ipv6.com/. However, conveying these addresses or MAC addresses like 8b:db:a8:f2:f1:72 can be challenging for non-technical individuals and can lead to errors. Additionally, this method does not provide historical data, particularly from previous issues.

The Process of Accessing the Internet

When attempting to reach a website, such as https://schiller.com, it is necessary to first access a DNS server. This server translates the host segment (schiller) combined with the Top Level Domain (com) of the URL into an IP address like 58.212.90.52. Furthermore, the type of your computer and browser is transmitted with every web request, for instance:
Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16.

Significance of Default Gateways

Typically, a default gateway is an automatically assigned address from DHCP. Usually ending in .1 or .254, the default gateway, such as 192.0.0.81, is where all traffic from your computer is routed onwards. For IPv6, more detailed information is available in our article how-to-fix-ipv6-connectivity/, and it can be checked on Mac or Linux with the following code:

ifconfig -a

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  192.0.0.81    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:b8b0:4330:e7c5:c685%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): {176.187.71.55, 38.220.151.29}
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 8b:db:a8:f2:f1:72
  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 4e:dc:f2:6e:4f:e1
}

Fixing Network Issues: Wired vs Wireless

When it comes to transferring data, you have the option of using a wired or wireless (Wi-Fi) medium at the physical and data layer to send the information to your router.

Tips for Apple macOS / OSX Users

No matter which version of OSX/macOS you’re running, whether it’s 10.11.7, 11.2.6, or 12.1.4, 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 extremely useful, especially for teams that are remote or embrace Work From Anywhere (WFA).

Utilizing Built-in Scripts

A useful tool on OSX/macOS is the sudo wdutil info command, 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 can be used to generate a variety of logs, although much of it is only relevant to wireless-related issues, similar to wdutil.

Running sudo nohup /usr/bin/sysdiagnose -u & will execute the tool in the background and write logs to /var/tmp/<blah>.tar.gz. For an interactive run (although there is minimal 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 using Finder with Cmd+Shift+G. Keep in mind that the file sizes are approximately 300MB.

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