Tag Archives: VPN

How to Copy Large Files over VPN or Other Unreliable Network Connections

Network Error While Copying

Large file transfer over VPN is a problem for many companies for a few reasons, transfer is unreliable, VPN traffic kills the Internet connection, and it is unproductive. This article will show you how to copy large files over VPN or other unreliable network connections, and some of the best software to deal with this, and best practices to deal with large file transfer, and how to ensure file integrity. These are, in my experience, the best way to do it. You have to evaluate yourself, if they work in your environment, and test a lot.

When copying files over VPN, there are a few problems that need to be addressed:

  • file transfer can be easily interrupted,
  • over saturating the VPN connection,
  • redirecting all the available traffic to the VPN connection
  • ensuring the transferred file is undamaged

Let’s talk a bit about all of these, why they are important, and how they affect the success of your file copy. This will give you, hopefully, a clearer image of the process.

Network Interruption – File Transfer Failed

When we talk about large file transfers, an interruption after a few hours of transfer is not a good thing, and if you take in consideration the time spent, and to only realize you have to do it again because the transfer failed. There are many reasons for the network to interrupt, and even a second is enough to corrupt your file. VPN is prone to network interruptions with large files, because it saturates the Internet bandwidth, and when other VPN clients try to use the VPN tunnel, the file transfer will be interrupted.
The fix for this is some kind of transfer resuming at both the server level and the client level. A few client-server protocols that support file resuming are: SMB, FTP, HTTP, rsync.

The easiest way to implement file transfer resuming in a corporate environment is through SMB and robocopy. Robocopy has a feature to copy in restartable network mode, so if the network goes down, it will automatically resume the transfer from where it left. The robocopy option to copy in restartable mode is /z as with the regular copy command.

robocopy /mir /z  X:\source-folder\ \\RemoteServer\RemoteFolder

Rsync has also a resume option, and it works great, but you have to make sure you use the network filesystem and not a locally mounted network directory. The command to transfer will be like this:

rsync -aP juser@server:/RemoteServer/Directory /Home/Local-Directory

Filezilla has an option to resume files after interruption, but there is a timeout setup by default. Make sure you set the timeout to 0, so that you can recover even after a few hours with no connection between server and client. Note, that this is not a good option if you have many clients, since it will keep open connections indefinitely.

Time Out Config for Resuming

Apache has also an option to allow file resuming, which is enabled by default. The disadvantage with Apache is that, by default it doesn’t support file upload. If you are determined to use Apache for this though, there are some ways to do it, you can start your research here: File Upload plugin for Apache

Over Saturation of the VPN Connection

The VPN connection is there for many users, don’t think that your file is the most important think in the world. If you take all of the bandwidth for your file transfer, other users might not perform daily important tasks.

The over saturation of the VPN connection can be avoided by implementing bandwidth limiting at the software level.

You can do that with SMB by using robocopy, at the client level. The command will look like this:

robocopy /mir /IPG:250  X:\source-folder\ \\RemoteServer\RemoteFolder

The IPG parameter is the one that controls the bandwidth; it’s the acronym for Inter Packet Gap, and with an IPG of 250, the transfer rate on a 100 MBps network is around 12.7 MBps. The lower the IPG, the higher the bandwidth saturation. The transfer rate will be different for different network speeds.

With FTP is going to be at the server level, it’s very simple if you use Filezilla FTP server. Just restrict the bandwidth to a safe limit, (note that there is no restriction in the picture).

FileZilla configuration

Apache uses mod_ratelimit to control the bandwidth of its clients. For more information about that take a look at this page:

Rsync can also limit the bandwidth at the client level, and the option will be “–bwlimit”. A command to synchronize two folders with rsync, throttling the bandwidth, would look like this:

rsync –bwlimit=3000 /local/folder user@RemoteHost:/remote/backup/folder/

The 3000 means 3000 kbps. IMPORTANT, if you use

Control VPN Traffic

It looks like a simple decision to allow all the traffic possible through the VPN, most companies will determine that VPN traffic has the highest priority. However, in real life there are many non VPN applications that are run from the Internet, and are critical for a business. Booking a flight ticket, using a hosted web application, getting your emails from a hosted email server, etc… So it might make sense to control the maximum bandwidth used by the VPN, and this is especially needed in environments where large file transfers over VPN are very common. The best way to control this is through firewall policies to limit the bandwidth for the VPN destination. On some devices, like the Fortigate firewalls I am using, this is called traffic shaping.  On other devices might be named differently.

File Integrity Verification

There is a mechanism for checking the file integrity with robocopy and rsync.

The perfect tool to make sure your file is identical with the remote one is to check with md5. On Linux this is a package that comes by default in many distributions, on Windows you can use WinMD5, that you can download it here: WinMD5

MD5 checksum

How to – Debian Static IP Configuration

On a basic Debian machine without a graphical interface assigning the same IP address all the times can be achieved in two ways.

Static IP Address

To configure a static IP, (an IP that will never change), and not use DHCP you must edit the file /etc/networking/interfaces.
Insert the following code at the end of the file and don’t change anything else unless you know what you do:

# The first network card – this entry was created during the Debian installation
# (network, broadcast and gateway are optional)
#Private Interface
iface eth0 inet static
## only use gateway if your machine is not multi-homed, (two network cards). You can only have a default route.
# gateway

In our case the IP of the Debian machine is The gateway, (the router), is and it is a standard Class C network.

To refresh the network configuration without restarting the server execute:
/etc/init.d/networking restart

If that doesn’t work reboot the machine (reboot or init 6).

For a second network card you should add at the end of the file another entry for your second card:
#External interface
iface eth1 inet static

Check the new configuration by issuing the command:

DHCP Reserved address

If you want to set this via DHCP you have to make a reservation into your DHCP server for your network card’s MAC address.
You can find your MAC address by using the command ifconfig.
The server will spit some information on the screen that looks like this:
eth0 Link encap:Ethernet HWaddr 00:33:ff:c4:2f:2b
inet addr: Bcast: Mask:
inet6 addr: fe80::230:f4ff:fdd4:bf33/64 Scope:Link
RX packets:93373 errors:0 dropped:0 overruns:0 frame:0
TX packets:38320 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:76539317 (72.9 MiB) TX bytes:5551726 (5.2 MiB)
Interrupt:17 Base address:0x6000

The first line is the one you are interested in:
HWaddr 00:33:ff:c4:2f:2b
In your DHCP server make a reservation using 0033ffc42f2b as your MAC address. Note the removal of the colons in between.
Reboot the server and when the machine will try to renegociate its IP address the DHCP server will assign it the newly reserver address.

If you want to add a static route on your Debian machine edit your /etc/networking/interfaces file and add the following two lines at the end of your eth1, (eth0), configuration.
up route add -net netmask gw
down route del -net netmask gw
The two lines tell Debian to add a static route when the computer boots, and to remove the static route when it shuts down.

The parameters mean: is the network you want to make your Debian machine aware of; is the netmask of your added network, is the gateway to that network.

Why would you need a static network? In our configuration example your default route is through your public network interface.
Any additional internal networks or VPN’s will not be available. The configuration above tells your Debian machine how to reach any VPN or networks not reachable via the default Network.

There is another change needed if you plan to configure this machine as a simple router. You need to enable IP forwarding, in other words allow the machine to forward traffic for its clients.
# nano /etc/sysctl.conf
Change the following line : net.ipv4.ip_forward = 0
to net.ipv4.ip_forward = 1

Reboot the machine to make the setting active, or issue the following command to make the kernel aware of the change:
# echo 1 > /proc/sys/net/ipv4/ip_forward

Why do you want your Debian machine to connect to other networks or VPN’s? If your machine is a proxy, or a gateway it needs to know where to route packets for its clients. Even if your remote networks or VPN’s have their own proxy, if you have a shared server in one of these networks you need to make it available for your users. It is easier to maintain a static route on one server than add it to all of the clients.