Understand Mac Issues
Understanding Internet Addressing
When using the Internet, you are assigned a Public IPv4 address, such as 117.192.155.86, or an IPv6 address like 2000:9c6e:caaa:ccf1:f82d:a749:4a99:b46f. You can verify this information by visiting https://test-ipv6.com/. However, these addresses, along with MAC addresses like e0:35:eb:d5:8d:2e, can be challenging for non-technical individuals to communicate and can lead to errors. Moreover, historical data is not provided, which is crucial for addressing past issues.
Navigating the World Wide Web
When accessing a website such as https://ratke-walter.name, your request is first processed by a DNS server, which translates the URL’s host portion (ratke-walter) and the Top Level Domain (name) into an IP address like 23.114.88.222. Additionally, your computer and browser send their specifications with each web request, for example: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Safari/537.36.
The Significance of Default Gateways
The default gateway, typically obtained through DHCP, is an automatically configured address, such as 10.160.109.191 (usually ending in .1 or .254 based on the scope size). This gateway is responsible for routing all of your computer’s traffic. For IPv6, detailed instructions on troubleshooting connectivity can be found at how-to-fix-ipv6-connectivity/. Users of Mac or Linux can perform a check 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 10.160.109.191 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 fe80:5c4d:53e9:251:274%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): {214.109.28.60, 48.175.18.158}
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 e0:35:eb:d5:8d:2e
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 23:ea:0c:53:a2:7e
}
Resolving Connectivity Issues on Wired and Wireless Networks
When it comes to transmitting data to your router, you may use either a wired or a wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
No matter which version of OSX/macOS you are operating on, whether it’s 10.14.2, 11.0.8, or 12.2.5, 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 comes in handy, especially for teams that have embraced remote work and the Work From Anywhere (WFA) culture.
Utilizing Built-in Scripts for Assistance
A highly useful tool on OSX/macOS is the sudo wdutil info, which provides a dump of the current wireless settings to the CLI, and it can also be configured to generate specific logs for troubleshooting purposes. Moreover, the sysdiagnose tool can be used to generate a wide range of logs, although many of them are only point-in-time in relation to wireless, similar to wdutil.
By running sudo nohup /usr/bin/sysdiagnose -u &, the tool will run in the background and write logs to /var/tmp/<blah>.tar.gz. If you prefer to run it interactively, you can execute sudo /usr/bin/sysdiagnose and it will provide a privacy warning. When not run in the background, it should open Finder in the appropriate location, or you can navigate to /var/tmp using Finder with Cmd+Shift+G to point Finder to the path. However, be mindful of the file sizes, which are around 300MB or more.
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