General

Most of our customers face problems while configuring new clients in SEP sesam. Often the sources of the problems are misconfigured DNS Servers or no functional DNS at all. This document describes how to use SEP sesam with DNS names and how to check whether if your DNS configuration is OK.

Requirements and Rules

• SEP sesam needs a proper DNS to work, it will NOT work with IP Addresses only
• All DNS Names have to correctly resolve forward and reverse
• If no DNS Server is available, the hosts file of the client and backup server have to be used for making systems available via DNS name
• The Hostname of the SEP sesam Server must not include an underscore "_" sign (see Wikipedia)

Configuration

Common Error Messages

There are some common error messages which are an indication for errors in your name resolution:

Login incorrect. Client resolves his IP address [X.X.X.X] to [RANDOM_HOSTNAME], but server resolves it to [X.X.X.X]. Please adjust your name resolution. (0)

Hosts Files

Linux

If a hosts file has to be used because of no DNS servers in your network, the file on the system is placed in:

Windows

If you want to use a hosts file on windows Systems for working around DNS problems, the file can be found in:

Tools to check DNS Resolution

There are various tools which can be used to check the DNS resolution, they have up and downsides. The recommended way to check your DNS configuration is to use sm_setup check_resolution

ping

ping is not a proper tool to check DNS resolution, it will not always be 100% correct. It is also not possible to correctly reverse resolve the DNS names.

nslookup (Windows and Linux)

This tool can be used to query and existing DNS Server for a certain hostname or ip address. It will NOT check the hosts file of the System. As such, you may get different results if you choose to use nslookup. SEP sesam resolves its hostnames via 'common library function' and will first use the hostname specified in the hosts file of the system.

host (linux only)

As nslookup, host can be used to forward and reverse resolve hostnames and ip addresses. It defaults to the name server configured in /etc/resolv.conf but can also be used wit a certain DNS Server as an additional argument. It will query the DNS Server of the System first.

sm_setup check_resolution (recommended)

This is the recommended way to check your DNS Resolution. Both SEP sesam Client and SEP sesam Servers come with the SEP sesam tool "sm_setup" installed. It can be used to forward and reverse resolve DNS names from the Command Line.

Before you can use this tool, be sure to execute the SEP sesam profile like shown in this FAQ entry:

A support staff member told me to set a profile, what does he mean?

It is recommended to run this command on the backup server AND on the client with different arguments. On the backup server, the second argument will be the desired hostname of the client. If executing the command at the client, the second argument will be the hostname of the backup server.

The output of the command looks like this:

As you can see the command will output the forward and reverse resolved hostname of the system. Both the addresses and hostnames which are returned have to match. For example if the Official name which is returned from the reverse resolve is different from the one specified on the command line, this will result in problems backing up the client (see Common Error Messages).

The same values have to match on the client for the hostname of the backup server: