There are 3 things to keep in mind when entering nameserver information for .DE domain names.

• The first 3 bits of the IP address (C-class) is different for each nameserver.
• A glue record is necessary for the domain on the nameservers.
• The SOA (Start of Authority) must be within the following guidelines:

refresh : 10000 - 86400
retry: 1800 -28800
expire: 604800 - 3600000
ttl: 180 - 345600

You can go to Zone Check to check the zone file for your domain.