Artifactory does not allow to save a server name starting with a number in 4.x. - This was allowed in 3.x.
Steps to reproduce:
1. Go to the Artifactory UI --> Admin --> Configuration --> General
2. Try to enter a name starting with digits - you will be prompted with:
"Name cannot be blank or contain spaces & special characters"
Important point to mention:
Deploying a config descriptor using the REST API with a server name starting numericly, will deploy and apply successfully.
This used to be allowed in 3.x.
RFC 1123 - Relaxes a constraint of RFC 952 which specifies a legacy of the Hostname Server Protocol (described in RFC 953) replaced by DNS. So a fully numeric hostname would be valid per these RFCs.
RFC 1178 - Provides guidelines to choose a valid hostname because of implementations issues. A lot of these implementations don't recognize numeric hostnames well and try to parse them as if they were IPs until they contain at least one non-numeric character no matter the location.
However: There are well-known web-sites starting (or even only containing) numbers: