When using the Internet, individuals often have a Public IPv4 address, such as 177.104.108.191
, or an IPv6 address like 2000:68e6:921c:5fa7:48b6:7745:75e9:f9a4
. One can verify their address at https://test-ipv6.com/, however, non-technical users may find it challenging to communicate or identify MAC addresses like a4:46:62:93:ee:48
. This can lead to errors and complications. Moreover, it fails to provide historical data, especially in relation to past issues.
When attempting to access a website, such as https://reilly.io, the initial step involves contacting a DNS server to translate the host portion (reilly) combined with the URL’s Top Level Domain (io) into an IP address, for example, 144.149.212.71
. Moreover, the computer and browser include their type in all web requests, for instance:
Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36
The default gateway is typically an automatically configured address through DHCP. Users receive a default gateway, such as 192.168.32.93
(usually ending in .1 or .254 based on scope size), where the computer forwards all traffic for routing. To explore IPv6 further, a detailed guide is available at how-to-fix-ipv6-connectivity/, and on Mac or Linux, the configuration can be checked using the command:
ifconfig
netstat -rn -f inet | egrep -i "default|0/1|128.0/1"
0/1 172.18.12.193 UGScg utun3 default 192.168.32.93 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.
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 fe80:6fb6:e77c:112f:5a3c%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.
To get a look at the low level DHCP configuration (Mac/Linux):
ipconfig getpacket en0
... domain_name_server (ip_mult): {241.23.35.93, 29.157.242.159} 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 a4:46:62:93:ee:48 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 90:46:b1:da:34:06 }
When dealing with the physical and data layer, it is important to consider whether the medium used is wired or wireless (Wi-Fi) when sending data to the router.
Regardless of the version of OSX/macOS being used, whether it’s 10.11.8
, 11.3.9
, or 12.1.5
, there are various tools available for troubleshooting. Unfortunately, the manual actions and scripts do not provide a series of correlated values over time. This is where automated remote troubleshooting becomes essential, especially for teams that are embracing remote work and Work From Anywhere (WFA).
One useful tool on OSX/macOS is the sudo wdutil info
command, which provides a dump of current wireless related settings to the CLI, and can also be configured to 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 at a specific point in time, similar to wdutil.
Running sudo nohup /usr/bin/sysdiagnose -u &
in the background will write logs to /var/tmp/<blah>.tar.gz
for you. If you prefer to run it interactively (although there isn’t much interaction), you can executesudo /usr/bin/sysdiagnose
, which will prompt a privacy warning. When not run in the background, it should open Finder in the correct location, or you can navigate to /var/tmp
or use Finder with Cmd+Shift+G to specify the path. Keep in mind that the file sizes are approximately 300MB.
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