How Do You Troubleshoot OSX Connectivity
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 254.42.38.178, or an IPv6 address like 2000:2fb9:7cb4:afdc:1c36:6afd:225c:a01e. You can verify this at https://test-ipv6.com/. However, for those who are not tech-savvy, conveying these addresses, or even MAC addresses like 39:83:61:04:bc:38, can quickly become error-prone and complex. Furthermore, this method does not provide any historical data, especially for past issues.
Navigating the World Wide Web
When accessing a webpage like https://jacobs-purdy.info, the first step is to contact a DNS server in order to translate the host portion (jacobs-purdy) in combination with the Top Level Domain (info) of the URL into an IP address, such as 75.223.56.229. Your computer and browser send their type along with all web requests, for 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
Usually, your default gateway is an address that is automatically configured via DHCP. This default gateway, such as 192.0.0.90 (typically ending in .1 or .254 depending on the scope size), is where your computer forwards all its traffic to be routed further. For IPv6, you can delve deeper into this topic in how-to-fix-ipv6-connectivity/. Alternatively, you can verify this on a Mac or Linux by using:
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 192.0.0.90 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 fe80:132a:a646:7931:ee6d%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): {150.218.252.199, 97.196.216.46}
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 39:83:61:04:bc:38
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 29:5a:39:03:3d:39
}
Resolving Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are running, whether it’s 10.14.1, 11.2.1, or 12.2.7, there are various troubleshooting tools available. However, manual actions and scripts fail to provide a set of correlated values over time. This is where automated remote troubleshooting becomes essential, particularly for teams implementing remote work and Work From Anywhere (WFA).
Available Built-in Scripts for Assistance
An extremely 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 employed to generate a wide range of logs, although much of it is only relevant to the wireless network at a specific point in time, 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 you. For an interactive run (although there is minimal interaction), you can use the command sudo /usr/bin/sysdiagnose, which will prompt a privacy warning. When not run in the background, it should open Finder in the appropriate location, where you can then navigate to /var/tmp, or use Cmd+Shift+G in Finder to point to the path. Just be mindful of the file sizes, which can be around 300MB or so.
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