Overview
In a DNS experience Test, on selecting the protocol as TCP in the Advanced Settings (as shown in the image below), there is a possibility that the test will fail with the following errors:
206[Invalid argument]
255[Unknown socket error]
The 'Invalid argument' error is seen only on nodes with IPv6 protocol whereas the 'Unknown socket layer' error occurs on all nodes.
Note: The above-mentioned errors are not seen when the default protocol UDP is used.
These errors cannot be deemed as a Catchpoint defect, as the TLDs have IPV6 issues. This is a problem with the internet generally.
Explanation
DNS with UDP imitates the user experience in resolving a specific IP. Most DNS requests and responses are small in size (less than 512 bytes) so users mostly use UDP, a best-effort protocol. Even though it is less reliable than TCP, it is faster and well-suited for small amounts of data.
TCP must be used to exchange information larger than 512 bytes. So, when trying to exchange larger amounts of information, the TLDs are not able to resolve the requests, resulting in such errors
Solution
In order to eliminate such issues, choose the below settings from the Advanced Settings section:
