Understand Mac Internet
Understanding Internet Addressing
When connecting to the Internet, you are assigned either a Public IPv4 address (e.g. 244.229.120.22) or an IPv6 address (e.g. 2000:a98f:d1bd:9caa:59f2:2a49:fde5:eec1). You can verify this using https://test-ipv6.com/. However, for those who are not technically inclined, conveying these addresses, or even referencing MAC addresses like 1d:bd:f3:ac:81:ea, can be error-prone and quickly become complex. Moreover, this method does not provide any historical data, especially from past issues.
Navigating the World Wide Web
In order to access a website such as https://ullrich-cronin.com, your computer interacts with a DNS server to convert the host portion (ullrich-cronin) along with the Top Level Domain (com) of the URL into an IP address (e.g. 57.178.148.46). Your computer and browser also include their type in all web requests, for instance Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko
The Significance of Default Gateways
Your default gateway is typically an automatically assigned address through DHCP. This is the address your computer forwards all its traffic to be routed onwards. While default gateways for IPv6 are discussed in depth in the article how-to-fix-ipv6-connectivity/, you can verify them on Mac or Linux by using:
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 172.22.96.94 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:e8f7:64b1:4241:36f2%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): {189.26.202.176, 168.86.147.74}
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 1d:bd:f3:ac:81:ea
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 b7:77:c8:15:e9:c2
}
Solve Problems with Wired or Wireless Connections
When it comes to sending data to your router, you might be using either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you have - whether it’s 10.15.3, 11.3.3, or 12.3.8 - there are various tools available for troubleshooting. However, these manual methods and scripts fail to provide a set of correlated values over time. This is where automated remote troubleshooting becomes invaluable, especially for teams that embrace remote work and Work From Anywhere (WFA).
Useful Scripts That Come Included
One of the most useful tools in OSX/macOS is the sudo wdutil info command, which provides a dump of current wireless settings to the CLI and can also generate specific logs for troubleshooting. Additionally, the sysdiagnose tool can be used to generate a wide range of logs, although much of it is only relevant to wireless settings, similar to wdutil.
To run it in the background and save logs to /var/tmp/<blah>.tar.gz, use the command sudo nohup /usr/bin/sysdiagnose -u &. Alternatively, you can run it interactively with the command sudo /usr/bin/sysdiagnose, but be cautious of the large file sizes of around 300MB.
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