How Can I Troubleshoot Mac No-access
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 126.215.253.172 or an IPv6 address like 2000:29f:40f0:f7a5:4243:d57e:e441:1ca7. You can verify this information by visiting https://test-ipv6.com/. However, explaining or even discussing these addresses, or even MAC addresses like a2:79:11:e9:60:2f, with individuals who are not technologically savvy can be prone to errors and become complex. Additionally, this method does not provide any historical data, especially regarding previous issues.
Navigating the World Wide Web
When attempting to reach a web page, such as https://oconnell-douglas.info, you initially connect to a DNS server to translate the host portion (oconnell-douglas) combined with the Top Level Domain (info) of the URL to an IP address like 195.199.50.163. Your computer and browser actually sends its type with all web requests, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
Your default gateway is typically an automatically configured address through DHCP. This default gateway, such as 10.39.201.14 (usually ending in .1 or .254 depending on the scope size), is where your computer sends all of its traffic to be routed onwards. For information regarding IPv6, there is an in-depth guide available at how-to-fix-ipv6-connectivity/. However, you can also check on Mac or Linux 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 10.39.201.14 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:c2f9:8191:aa18:1841%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): {69.33.237.115, 66.225.67.241}
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 a2:79:11:e9:60:2f
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 2e:df:db:3e:73:9c
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be utilizing a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Solutions for Apple macOS / OSX
Regardless of which version of OSX/macOS you’re operating on, whether it’s 10.15.7, 11.0.3, or 12.1.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes extremely beneficial, particularly for teams that are embracing remote work and Work From Anywhere (WFA).
Built-in Tools That Can be Utilized
An extremely useful tool on OSX/macOS is “sudo wdutil info” which provides a dump to the command line interface of current wireless related settings. It can also be configured to generate specific logs for troubleshooting. Additionally, the “sysdiagnose” tool can be used to generate a wide array of logs, although much of it is point-in-time related to wireless, similar to wdutil.
To run “sysdiagnose” in the background and write logs to “/var/tmp/
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