Fix OSX No-access
Explaining Internet Addressing
When using the Internet, you are assigned a unique address, such as the IPv4 address 186.126.29.112 or the IPv6 address 2000:d853:2a1a:cb52:2321:54d2:4b07:e93e. You can verify this information at https://test-ipv6.com/. However, communicating these addresses can be complicated for non-technical individuals, especially when dealing with MAC addresses like a5:a0:1b:72:a6:46. Moreover, this method does not provide historical data related to past issues.
How Web Access Works
When accessing a web page, such as https://jones.co, you first connect to a DNS server to translate the URL’s host portion (jones) along with the Top Level Domain (co) to an IP address, like 122.25.76.130. Your computer and browser indicates their type with each web request, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
Understanding the Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. A default gateway, such as 172.31.201.34 (usually ending in .1 or .254 depending on the scope size), is where a computer sends all of its traffic to be routed. For IPv6 connectivity issues, you can refer to a detailed guide at how-to-fix-ipv6-connectivity/, or use the following commands on Mac or Linux to check the settings:
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 172.31.201.34 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 fe80:2663:afb2:ffd4:e32e%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): {154.186.174.34, 114.105.137.79}
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 a5:a0:1b:72:a6:46
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 6f:66:da:03:bf:1f
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to transmitting data to your router, you may be using either 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 are currently using—whether it’s 10.13.1, 11.4.7, or 12.2.9—there are various tools available for troubleshooting. However, manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams who have adopted remote work and Work From Anywhere (WFA).
Effective Built-in Scripts for Troubleshooting
An extremely useful tool on OSX/macOS is sudo wdutil info, which provides a dump of the current wireless related settings to the CLI. It can also be configured to generate specific logs for troubleshooting. Additionally, the sysdiagnose tool offers a more comprehensive option for generating a wide range of logs (although many are only point-in-time in relation to wireless, 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. If you prefer to run it interactively (although there isn’t much interaction), you can runsudo /usr/bin/sysdiagnose and it will provide 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 be mindful of the file sizes, which are approximately 300MB or more.
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