Troubleshoot Mac Internet Connection
The Functioning of Internet Addressing
When connecting to the Internet, you are assigned a Public IPv4 address, such as 95.89.204.248, or an IPv6 address, like 2000:e4b2:cfeb:e70:4ac:9dc2:1ee1:f745. Verification of this can be done at https://test-ipv6.com/. However, for individuals who are not technologically savvy, relaying and communicating these addresses, or even calling out MAC addresses like f5:94:f8:60:74:a5, can introduce errors and complex challenges. Also, this method fails to provide historical data, particularly from past occurrences of problems.
Navigating the Internet
In order to access a website such as https://west-hartmann.info, the initial step involves querying a DNS server to convert the host portion (west-hartmann) along with the Top Level Domain (info) of the URL into an IP address, like 213.101.163.94. Computers and web browsers send their type along with all web requests, for example: Mozilla/5.0 (compatible; MSIE 9.0; AOL 9.7; AOLBuild 4343.19; Windows NT 6.1; WOW64; Trident/5.0; FunWebProducts)
The Significance of Default Gateways
The default gateway is typically an address that is automatically configured through DHCP. You receive a default gateway, such as 192.0.0.204 (usually ending in .1 or .254 depending on the scope size), and this is the designated point where your computer directs all its traffic to be routed onward. For IPv6, a detailed examination of how-to-fix-ipv6-connectivity/ is available, but you can verify on Mac or Linux by:
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 192.0.0.204 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 fe80:3d97:6df3:2c4e:e8ff%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): {206.165.156.232, 4.95.170.151}
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 f5:94:f8:60:74:a5
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 94:bf:6e:23:40:e9
}
Resolve Issues with Wired and Wireless Connections
When it comes to transmitting data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of whether you are operating on OSX/macOS version 10.15.1, 11.1.9, or 12.2.2, there are various troubleshooting tools available. However, these tools do not provide a series of correlated values over time, which is a drawback when it comes to manual actions and scripts. This is where automated remote troubleshooting proves to be beneficial, especially for teams that have adopted remote work and Work From Anywhere (WFA) practices.
Useful Built-in Scripts
One highly beneficial tool for OSX/macOS is the sudo wdutil info, which delivers a dump of current wireless settings to the CLI and can also be configured to generate specific logs for troubleshooting. Moreover, the sysdiagnose tool is even more comprehensive as it can generate a wide array of logs, although much of it pertains to wireless settings and is only point-in-time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & in the background will result in logs being written to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, which will display a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp manually. It’s important to note that the file sizes are approximately 300MB.
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