Check Mac Issues
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address such as 35.134.45.112 or an IPv6 address like 2000:3b05:f579:9a34:bbac:63f6:c8d3:8386. These addresses can be verified at https://test-ipv6.com/. However, conveying these addresses to non-technical individuals, or referencing MAC addresses such as 37:f0:16:32:f9:ad, can lead to errors and complexity. Furthermore, historical data is not provided, particularly in the context of past issues.
Navigating the World Wide Web
When accessing a website like https://kuphal.net, you first contact a DNS server to convert the host portion (kuphal) and the Top Level Domain (net) of the URL into an IP address, such as 52.9.200.150. Your computer and browser include their type in 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 assigned automatically through DHCP. A common default gateway, such as 192.168.156.115 (usually ending in .1 or .254 based on the scope size), is where your computer directs all its traffic to be routed. For IPv6, a comprehensive guide can be found at how-to-fix-ipv6-connectivity/, but it can also be checked 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 192.168.156.115 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 fe80:6a83:a38f:6883:8cd2%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): {245.162.199.15, 99.105.207.241}
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 37:f0:16:32:f9:ad
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 d0:15:c4:e2:d8:59
}
Resolve Connectivity Issues: Wired vs Wireless
When it comes to sending data to your router, you may be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Effective Solutions for Apple macOS / OSX Users
Regardless of the version of OSX/macOS you are using, whether it’s 10.14.6, 11.2.8, or 12.0.4, there are various troubleshooting tools available. However, these manual actions and scripts do not provide a series of correlated values over time, making it difficult for teams embracing remote work and Work From Anywhere (WFA). This is where automated remote troubleshooting comes in handy.
Useful Built-in Tools for Troubleshooting
On OSX/macOS, the sudo wdutil info tool is quite helpful as it provides a dump of current wireless settings to the CLI and can also be configured to generate specific troubleshooting logs. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is point-in-time data related to wireless, similar to wdutil.
To run sysdiagnose in the background and generate logs in /var/tmp/<blah>.tar.gz, you can use the command sudo nohup /usr/bin/sysdiagnose -u &. If you prefer to run it interactively, you can use sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of about 300MB. Remember to navigate to /var/tmp or use Finder with Cmd+Shift+G to locate the file.
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