Deploying on the network is usually very straightforward – especially since much of the networking support is typically built into the DLP server.

If you encounter complications they are generally:

  • due to proxy integration incompatibilities,
  • around integrating with a complex email infrastructure (e.g., multiple regions), or
  • in highly distributed organizations with large numbers of network egress points.

Passive sniffing

Sniffing is the most basic network DLP monitoring option. There are two possible components involved:

  • All full-suite DLP tools include network monitoring capabilities on the management server or appliance. Once you install it, connect it to a network SPAN or mirror port to monitor traffic.
  • Since the DLP server can normally only monitor a single network gateway, various products also support hierarchical deployment, with dedicated network monitoring DLP servers or appliances deployed to other gateways. This may be a full DLP server with some features turned off, a DLP server for a remote location that pulls policies and pushes alerts back to a central management server, or a thinner appliance or software designed only to monitor traffic and send information back to the management server.

Integration involves mapping network egress points and then installing the hardware on the monitoring ports. High-bandwidth connections may require a server or appliance cluster; or multiple servers/appliances, each monitoring a subset of the network (either IP ranges or port/protocol ranges).

If you don’t have a SPAN or mirror port you’ll need to add a network tap. The DLP tool needs to see all egress traffic, so a normal connection to a switch or router is inadequate.

In smaller deployments you can also deploy DLP inline (bridge mode), and keep it in monitoring mode (passthrough and fail open). Even if your plan is to block, we recommend starting with passive monitoring.


Email integrates a little differently because the SMTP protocol is asynchronous. Most DLP tools include a built-in Mail Transport Agent (MTA). To integrate email monitoring you enable the feature in the product, then add it into the chain of MTAs that route SMTP traffic out of your network.

Alternatively, you might be able to integrate DLP analysis directly into your email security gateway, if your vendors have a partnership.

You will generally want to add your DLP tool as the next hop after your email server. If you also use an email security gateway, that means pointing your mail server to the DLP server, and the DLP server to the mail gateway.

If you integrate directly with the mail gateway your DLP tool will likely add x-headers to analyzed mail messages. This extra metadata instructs the mail gateway how to handle each messages (allow, block, etc.).

Web gateways and other proxies

As we have mentioned, DLP tools are commonly integrated with web security gateways (proxies) to allow more granular management of web (and FTP) traffic. They may also integrate with instant messaging gateways, although that is very product specific.

Most modern web gateways support something called the ICAP protocol (Internet Content Adaptation Protocol) for extending proxy servers. If your web gateway supports ICAP you can configure it to pass traffic to your DLP server for analysis. Proxying connections enable analysis before the content leaves your organization. You can, for example, allow someone to use webmail but block attachments and messages containing sensitive information.

So much traffic now travels over SSL connections that you might want to integrate with a web gateway that performs SSL interception (also called a “reverse proxy”). These work by installing a trusted server certificate on all your endpoints (a straightforward configuration update) and performing a “man-in-the-middle” interception on all SSL traffic. Traffic is encrypted inside your network and from the proxy to the destination website, but the proxy has access to decrypted content.

Note: this is essentially attacking and spying on your own users, so we strongly recommend notifying them before you start intercepting SSL traffic for analysis.

If you have SSL interception up and running on your gateway, there are no additional steps beyond ICAP integration.

Additional proxies, such as instant messaging, have their own integration requirements. If the products are compatible this is usually the same process as integrating a web gateway: just turn the feature on in your DLP product and point both sides at each other.

Hierarchical deployments

Until now we have mostly described fairly simple deployments, focused on a single appliance or server. That’s the common scenario for small and some mid-size organizations, but the rest of you have multiple network egress points to manage – possibly in very distributed situations, with limited bandwidth in each location.

Hopefully you all purchased products which support hierarchical deployment. To integrate, you place additional DLP servers or appliances on each network gateway, then configure them to slave to the primary DLP server/appliance in your network core. The actual procedure varies by product, but here are some things to look out for:

  • Different products have different management traffic bandwidth requirements. Some work great in all situations, but others are too bandwidth-heavy for some remote locations.
  • If your remote locations don’t have a VPN or private connection back to your core network, you will need to establish them for handle management traffic.
  • If you plan on allowing remote locations to manage their own DLP incidents, now is the time to set up a few test policies and workflow to verify that your tool can support this.
  • If you don’t have web or instant messaging proxies at remote locations, and don’t filter that traffic, you obviously lose a major enforcement option. Inconsistent network security hampers DLP deployments (and isn’t good for the rest of your security, either!).
  • We are only discussing multiple network deployments here, but you might use the same architecture to cover remote storage repositories or even endpoints.

The remote servers or appliances will receive policies pushed by your main management server and then perform all analysis and enforcement locally. Incident data is sent back to the main DLP console for handling unless you delegated to remote locations.

As we have mentioned repeatedly, if hierarchical deployment is a requirement, please be sure to test this capability before putting money down on a product. This is not the sort of problem you want to try solving during deployment.