How Do You Support Mac No-access
Understanding Internet Address Allocation
When connecting to the Internet, you are assigned a public IPv4 address such as 247.124.56.222 or an IPv6 address like 2000:744b:47e0:44e5:ae29:ea26:9540:638c. It is possible to verify this information by visiting https://test-ipv6.com/. However, conveying these addresses to individuals who are not technologically savvy, or even mentioning MAC addresses such as ac:a2:6e:23:a9:2c, can lead to errors and become complex quite rapidly. Moreover, this method does not provide any historical data, especially from previous incidents.
Navigating Websites
In order to access a website like https://kerluke-cronin.io, you must first contact a DNS server to convert the host segment (kerluke-cronin) in combination with the Top Level Domain (io) of the URL into an IP address, for example 234.155.12.11. Whenever a web request is made, your computer and browser disclose their type, such as Mozilla/5.0 (Windows; U; Win 9x 4.90; SG; rv:1.9.2.4) Gecko/20101104 Netscape/9.1.0285.
Understanding the Significance of Default Gateways
Typically, your default gateway is an address that is automatically configured through DHCP. This address could take the form of 192.168.192.198 (although they generally end in .1 or .254 based on the size of the network) and this is where your computer directs all its traffic to be routed onward. Detailed instructions for checking on Mac or Linux can be found in our blog post how-to-fix-ipv6-connectivity/.
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 192.168.192.198 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:dbfd:f400:1b5f:1b51%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): {42.0.107.171, 255.231.178.52}
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 ac:a2:6e:23:a9:2c
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 df:ee:f9:6d:a3:99
}
How to Troubleshoot and Resolve Connectivity Issues
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.
Steps for Resolving Issues on Apple Mac OS
Regardless of whether you are using OSX or macOS, whether it’s version 10.14.9, 11.1.3, or 12.1.3, 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 invaluable, especially for remote work and Work From Anywhere (WFA) teams.
Effective Built-in Scripts for Assistance
A useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless-related settings to the CLI and can be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool can be used to produce a wide range of logs, although much of it is related to wireless settings and is only a snapshot in time, similar to wdutil.
To run it in the background and write logs to /var/tmp/<blah>.tar.gz, you can use this command:sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, for an interactive run, you can execute: sudo /usr/bin/sysdiagnose while being mindful of the large file sizes of about 300MB.
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