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Understanding Internet Address Allocation
When using the Internet, you will be assigned a unique Public IPv4 address, such as 171.59.30.180, or an IPv6 address like 2000:b5b8:56a7:5a8:e4d:818e:af63:a67d. These addresses can be verified at https://test-ipv6.com/. However, conveying these addresses to individuals who are not technologically savvy, or even mentioning MAC addresses like 92:e7:87:56:03:36, can quickly become complicated and error-prone. Furthermore, this method does not provide any historical data and is particularly ineffective when addressing past issues.
Navigating the World Wide Web
When attempting to access a website such as https://zulauf.co, you first connect to a DNS server to translate the host portion (zulauf) in combination with the Top Level Domain (co) of the URL into an IP address, such as 0.167.239.46. Your computer and browser include information about their type in all web requests, for example:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured via DHCP. You will receive a default gateway, such as 192.168.45.48 (usually ending in .1 or .254 based on the scope size of the network), and this is where your computer forwards all its traffic to be routed further. For IPv6, we provide a comprehensive guide on how-to-fix-ipv6-connectivity/, and you can check this on Mac or Linux by using the following command:
```bash
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 192.168.45.48 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 fe80:7377:3e89:debe:897f%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): {23.155.208.209, 117.80.154.227}
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 92:e7:87:56:03:36
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 d2:5e:49:e7:8c:44
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data, the physical and data layer can involve either a wired or wireless (Wi-Fi) medium to send the data to your router.
Troubleshooting Tips for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, such as 10.15.5, 11.3.9, or 12.0.7, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are working remotely and embracing the concept of Work From Anywhere (WFA).
Useful Built-in Scripts
One valuable tool on OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the command-line interface (CLI) and can also be used to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to produce a wide range of logs, although many are only point-in-time related to wireless, similar to wdutil.
To run sysdiagnose in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u & If you prefer to run it interactively, use the command sudo /usr/bin/sysdiagnose and be aware of the large file sizes of about 300MB.
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