How To Troubleshoot MacOS Internet
Understanding How Internet Addresses are Assigned
When you are connected to the Internet, you are assigned a Public IPv4 address, such as 16.226.149.197, or an IPv6 address, like 2000:56e8:ba38:c62b:d12a:458a:655e:aa63. It is possible to verify these addresses through https://test-ipv6.com/. However, for individuals who are not well-versed in technology, conveying these addresses or even referring to MAC addresses, like 0c:af:64:0f:d3:b4, can be prone to errors and become complex very quickly. Moreover, this method does not provide any historical data, especially related to past issues.
Navigating the Internet
In order to access a webpage, such as https://orn.biz, you initially connect to a DNS server to translate the combination of the host (orn) and the Top Level Domain (biz) of the URL into an IP address, such as 6.88.242.66. Every web request from your computer and browser includes its type, for example:Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
Your default gateway is typically an address that is automatically configured through DHCP. You are assigned a default gateway, such as 192.168.255.114 (usually ending in .1 or .254, depending on the scope size), and this is where your computer sends all its traffic to be forwarded. For IPv6, we provide a detailed analysis in our how-to-fix-ipv6-connectivity/ blog post, and you can also perform a check on Mac or Linux 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 192.168.255.114 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 fe80:4c0b:7548:b574:ba7%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): {46.239.51.200, 242.228.169.0}
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 0c:af:64:0f:d3:b4
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 e3:e7:0d:db:8f:b1
}
Resolving Connectivity Issues with Wired and Wireless Networks
When it comes to transferring data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX
Regardless of whether you are running OSX/macOS versions such as 10.13.8, 11.0.9, 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. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).
Harnessing the Power of Built-in Scripts
On OSX/macOS, the sudo wdutil info tool proves to be very useful as it provides a dump of current wireless settings to the CLI, and can also generate specific logs for troubleshooting. For a more comprehensive approach, the sysdiagnose tool can be utilized to generate a wide range of logs, although many are only relevant at a specific point in time in relation to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (although there is minimal interaction), you can executesudo /usr/bin/sysdiagnose, which will prompt 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 with Cmd+Shift+G. Just keep in mind that the file sizes may be around 300MB, more or less.
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