How To Understand Apple Internet
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 101.119.240.116, or an IPv6 address like 2000:af5:c1d7:5cfb:beb1:8c28:f7c7:85f6. You can verify this information by visiting https://test-ipv6.com/. However, explaining and communicating these addresses, as well as MAC addresses like 96:50:35:64:38:10, can be error-prone and complex, especially for those who are not tech-savvy. Moreover, it does not provide any historical data, particularly from past issues.
Navigating the World Wide Web
When attempting to access a web page, such as https://parisian.biz, you first contact a DNS server to convert the host portion (parisian) combined with the Top Level Domain (biz) of the URL into an IP address like 247.116.9.51. Furthermore, every web request from your computer and browser includes its type, for example: Opera/9.80 (X11; Linux i686; Ubuntu/14.10) Presto/2.12.388 Version/12.16
The Significance of Default Gateways
The default gateway is typically an automatically configured address via DHCP. This default gateway, such as 192.168.152.173, (generally ending in .1 or .254 depending on the scope size) is where your computer sends all its traffic to be routed onwards. For IPv6, a comprehensive guide is available at how-to-fix-ipv6-connectivity/, and you can perform a check on Mac or Linux using the following command:
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 192.168.152.173 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 fe80:8f61:9a74:d211:9f60%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): {104.134.127.41, 29.153.174.151}
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 96:50:35:64:38:10
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 06:fb:d0:8d:5f:04
}
Troubleshooting Connectivity Issues in Wired and Wireless Networks
When it comes to sending data to your router, you may be utilizing either a wired or wireless (Wi-Fi) medium at the physical and data layer.
Solutions for Connectivity Problems on Apple macOS / OSX
Regardless of the version of OSX/macOS you are using, whether it’s 10.11.2, 11.1.2, or 12.1.6, there are various tools available for troubleshooting. 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 teams that embrace remote work and Work From Anywhere (WFA).
Utilizing Built-in Scripts for Troubleshooting
One extremely useful tool on OSX/macOS is the sudo wdutil info command, which provides a dump of the current wireless settings to the CLI and can be configured to generate specific logs for troubleshooting purposes. In addition, the sysdiagnose tool can be utilized to generate a wide range of logs, although much of it is only point-in-time information related to wireless, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u & will execute it in the background and write logs to /var/tmp/<blah>.tar.gz for you. If you prefer to run it interactively (even though there’s not much interaction), you can run sudo /usr/bin/sysdiagnose, which will trigger 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 to point Finder to the path. However, beware of file sizes, which are typically around 300MB.
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