How To DiagnOSe OSX Issues
A Comprehensive Look at Internet Addressing
When it comes to Internet connectivity, you might receive a public IPv4 address such as 113.236.239.231 or an IPv6 address like 2000:457c:253c:7595:87f2:3468:2497:f53f. You can verify this information by visiting https://test-ipv6.com/. However, for individuals who are not well-versed in technology, conveying these addresses or identifying MAC addresses like 06:76:39:e5:c5:41 can be prone to errors and can become complex rapidly. Furthermore, this method does not provide any historical data.
Navigating the World Wide Web
In order to access a webpage, such as https://heidenreich.info, you initially connect to a DNS server to translate the host (heidenreich) combined with the Top Level Domain (info) of the URL into an IP address, such as 200.187.222.53. Every web request made by your computer and browser includes its type, 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.
Understanding the Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. You will receive a default gateway, such as 192.0.0.163 (although they usually end in .1 or .254, depending on the scope size), and this is where your computer forwards all its traffic to be routed onwards. For IPv6, more detailed information is available in our article how-to-fix-ipv6-connectivity/, and you can perform a check on Mac or Linux by using the following 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 192.0.0.163 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 fe80:8e11:40f2:eb5d:fa6%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): {51.236.241.43, 42.130.33.29}
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 06:76:39:e5:c5:41
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 31:76:dc:36:6c:08
}
Fixing Network Issues
When it comes to sending data to your router, you may encounter problems at the physical and data layer if you are using a wired or wireless (Wi-Fi) medium.
Resolving Problems on Apple’s Operating Systems
Regardless of whether you are using macOS or OSX, whether it’s version 10.11.9, 11.4.4, or 12.0.9, there are various troubleshooting tools available. However, these tools and scripts do not provide a series of correlated values over time, which is where automated remote troubleshooting becomes essential, especially for remote work and Work From Anywhere (WFA) teams.
Useful Native Scripts
A valuable 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 at a specific point in time, similar to wdutil.
To run the sysdiagnose tool in the background and write logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. For an interactive mode, you can run sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of about 300MB.
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