Hi Petr,
Set the instance parameter "snc/identity/as" to the specific name of the server.
For example: "snc/identity/as p:CN=IDS, OU=IT, O=CSW, C=DE" (Do not forget to add "p:" in front of the name, as shown below).
Then restart your server & try again.
Also correct/clear me on following.
1.You mapped your Internal IP on which saprouter is installed with the external IP (which is registered at SAP side).
2.You are able to ping this external IP from remote location or from internal as well with name resolution.
3.sapdp00 3299 entry available under /etc/services file.
And re post dev_rout & host file entries as well.
Thanks,
Gaurav