Requirements to set up a Client interface in PresSTORE 3
Posted by Sven Koester on 27 June 2008 14:02
This article describes the IP network requirements to set up a connection between a PresSTORE server and a client.

PresSTORE sets up a TCP/IP connection from the server to the clients port 8000. In order to acieve that, the following requirements must be fulfilled:
  1. The client must be reaceable via IP protocol. This requires that either the clients IP address is enterted in the client configuration, or the client name must be entered and that client name must be resolved by a DNS to the correct client address. Please test IP requirements like routing and name resolution outside of PresSTORE with the ping utility (see man ping or for windows users ping /?).
  2. The IP port that is used on the client site (port 8000 by default) must be reachable. Please note that the connection is set up from the server to the client, this is a bit unusual. When configuring a firewall, allow on the PresSTORE server site outgoing connections to port 8000 and on the client site incoming connections to port 8000.
  3. The connection between server and client may remain for a long time (hours) without traffic. Because of this, some Network connections like NAT/PAT mappers consider the line to be inactive and close it. This behaviour is not supported.
The following questions and ansers shall help to understand this concept in more detail:

Q: Can I backup clients with a dynamic IP address, e.g. a DHCP client?
A: Yes. Just enter the client name in the client configuration on the PresSTORE server and ensure the name is correctly resolved to an IP address by a DNS (domain name service).

Q: Must I provide a VPN (Virtual privacy network)?
A: This is not required from a technical point of view. However some network administrators do not allow other connections than through a VPN.
 
Q: Can I use Port mapping (PAT) or Address Mapping (NAT)?
A: Yes, this may make it neccessary to set a different client address or port in the client configuration dialog. Please be aware that such mappers may not close alleged inactive lines.

Q: When do I need data transfer compression ?
A: Data compression can be helpful when transferring data over a slow line like an internet connection or a leased line the compressed data is smaller and thus can be transferred faster, but the compression costs CPU power. Please note that data compression makes no sense when either:
- Most of the data is already in compressed format (like mpeg or jpeg files), or
- When the line already operates with data compression.

Q: Where should I use transfer encryption ?
A: PresSTORE supports data transfer encryption. This means that data is encrypted by the sender and decrypter by the receiver. This method makes sense when data is transferred over the internet without external security mechanisms like VPN. The use of encryption when server and client are inside a VPN or inside a (local) LAN is usually not required.

Q: How does the client connect to the server?
A: It does not. The server establishes a connection to the client. In case the client needs to communicate to the server, it uses that existing line.


Q: What can I do when the connection breakes down unexpected or the line slows down after a while without visible reason?
A: Many active components in modern IP networks have small buffers wich are very helpful when surfing in the internet. When running PresSTORE (e.g. Synchronize or Backup), the amount of data is hughe and these buffers are too small, namely when there is a part of the line slower than another (e.g. when using a small internet connection to connect two fast LANs). This effect may cause decreasing data transfer rates or connection breaks. We had reports from multiple sites that it may help to reduce the bandwitdh in the PresSTORE client configuration screen to reduce such effects and increase the data transfer time.


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