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The Fundamentals of Internet Addressing
When it comes to the Internet, you may be assigned a Public IPv4 address, such as 113.247.248.105, or an IPv6 address, like 2000:b883:4707:425d:1f65:85bb:9b35:bd27. To verify this, you can visit https://test-ipv6.com/. However, attempting to convey these addresses to individuals who are not tech-savvy, or even recite MAC addresses like 06:04:8f:5c:66:13, can be prone to errors and quickly become complex. Furthermore, this method does not provide any historical data, especially regarding past issues.
Navigating the World Wide Web
To access a website such as https://ferry.net, you must first contact a DNS server that translates the host portion (ferry) combined with the Top Level Domain (net) of the URL into an IP address, such as 254.228.189.164. Your computer and browser send their type with all web requests, for example:
<br>Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_3) AppleWebKit/537.75.14 (KHTML, like Gecko) Version/7.0.3 Safari/7046A194A```
The Significance of Default Gateways
Typically, your default gateway is an automatically configured address via DHCP. You are assigned a default gateway like 192.168.38.122 (usually ending in .1 or .254, depending on the scope size), and this is where your computer directs all of its traffic to be routed. For a detailed analysis of IPv6, refer to our article on how-to-fix-ipv6-connectivity/. However, it can also be checked on Mac or Linux with:
<br>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 192.168.38.122 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 fe80:932d:9d39:dce2:5e7c%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): {76.221.36.98, 175.28.214.44}
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 06:04:8f:5c:66:13
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 52:57:7f:81:b7:da
}
Resolving Issues with Wired and Wireless Connections
When transferring 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
Regardless of whether you are running OSX/macOS versions such as 10.11.4, 11.0.3, or 12.1.5, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a set of correlated values over time. For this reason, automated remote troubleshooting becomes essential, particularly for teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Assistance
One extremely useful tool on 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. Moreover, the comprehensive sysdiagnose tool can be used to produce a wide range of logs, though many are only relevant to wireless at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will generate logs in /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (despite minimal interaction), usesudo /usr/bin/sysdiagnose and heed the privacy warning. When not run in the background, Finder should open in the correct location, or you can navigate to /var/tmp or use Finder with Cmd+Shift+G to point to the path. Be mindful of the file sizes, which are approximately 300MB.
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