DiagnOSe Mcs Router Issues
A Tutorial on Internet Addressing
When it comes to the Internet, you might be assigned a Public IPv4 address such as 49.51.237.121 or an IPv6 address like 2000:222e:55fa:921:85ca:ef41:1ac4:7ddd. It’s possible to verify these addresses on https://test-ipv6.com/. However, expressing these addresses, or even referencing MAC addresses like f8:12:d8:2c:13:ef, can quickly become error-prone and complicated, especially for those who are not tech-savvy. Moreover, this method does not offer any historical data, particularly regarding past problems.
A Guide to Accessing the Internet
In order to access a web page like https://durgan.info, your computer initially contacts a DNS server to convert the host portion (durgan) combined with the Top Level Domain (info) of the URL to an IP address, such as 23.197.52.49. Every web request from your computer and browser actually includes its type, such as 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
Your default gateway is typically an automatically assigned address through DHCP. It is usually a default gateway like 10.239.29.215 (though its final digits typically end in .1 or .254, depending on the scope size) to which your computer directs all its traffic to be routed onwards. For a comprehensive explanation of IPv6, you can refer to our in-depth article on how-to-fix-ipv6-connectivity/. Alternatively, you can 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 10.239.29.215 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:c135:ebd2:6d27:8825%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): {50.137.20.215, 251.13.103.96}
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 f8:12:d8:2c:13:ef
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 90:51:e5:6d:d1:3c
}
Fixing Connectivity Issues for Wired and Wireless Networks
When it comes to sending data to your router, you might be using a wired or wireless (Wi-Fi) medium at the physical and data layer.
Troubleshooting Tips for Apple macOS / OSX Users
Regardless of whether you are on OSX or macOS versions like 10.11.4, 11.3.9, or 12.3.1, there are various troubleshooting tools available. However, these tools do not provide a set of correlated values over time, which is where automated remote troubleshooting becomes beneficial, particularly for teams that are remote or follow a Work From Anywhere (WFA) approach.
Helpful Scripts Already Available
One useful tool on 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. In addition to this, the sysdiagnose tool can be used to generate a wide range of logs, although most of them are point-in-time logs 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, simply run sudo /usr/bin/sysdiagnose and follow the privacy warning prompt. Keep in mind that the file sizes can be around 300MB.
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P.S. Tips For Remote Network and Client Support
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