Understand OSX Internet Connection
Explanation of Internet Addressing
When using the Internet, you might be assigned a Public IPv4 address, such as 201.220.126.187, or an IPv6 address, such as 2000:236e:f548:f5cd:d087:f2e6:15dc:236e. To easily verify these addresses, you can visit https://test-ipv6.com/. However, for those who are not well-versed in technology, attempting to communicate or identify MAC addresses like 53:60:29:aa:85:0f can lead to mistakes and unnecessarily complex situations. Additionally, this method does not offer access to historical data for past issues.
Navigating the World Wide Web
When attempting to reach a website, such as https://oconner.info, the first step is to connect to a DNS server, which will convert the host portion (oconner) and the Top Level Domain (info) of the URL into an IP address, such as 250.147.90.245. Additionally, your computer and browser will include its type in all web requests e.g. 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 automatically assigned address via DHCP, such as 172.27.244.21 (usually ending in .1 or .254 depending on the scope size). This is the destination to which your computer sends all its traffic to be routed onwards. For more information on establishing a IPv6 default gateway, visit how-to-fix-ipv6-connectivity/. On Mac or Linux, this can be verified 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 172.27.244.21 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 fe80:821a:4570:e167:1090%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): {243.250.172.154, 194.23.224.187}
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 53:60:29:aa:85:0f
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 9d:04:c5:80:bc:40
}
Resolving Issues with Wired and Wireless Connectivity
When it comes to transmitting data at the physical and data layer, you may be using either a wired or wireless (Wi-Fi) medium to send the data to your router.
Troubleshooting Methods for Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.13.7, 11.1.9, or 12.0.4, there are various tools available for troubleshooting. However, these manual actions and scripts do not provide a set of correlated values over time. This is where automated remote troubleshooting becomes valuable, especially for teams that are involved in remote work and Work From Anywhere (WFA) initiatives.
Useful Built-in Scripts
One useful tool on OSX/macOS is the sudo wdutil info command, 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 generate a wide range of logs related to wireless (although much of it is only relevant to 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. Alternatively, you can run sudo /usr/bin/sysdiagnose interactively, 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 Finder or use Cmd+Shift+G to navigate to the path. However, be mindful of the file sizes, which range around 300MB.
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