Reconciling DHCP Scopes

As time passes, you may experience what we call DHCP drift, which means the contents of your DHCP database no longer reflect accurately what's on your network. Although Microsoft doesn't make any prominent mention of this fact in the DHCP documentation, the DHCP server actually records lease information in two places: the DHCP database and the server's Registry. When you reconcile a scope, the DHCP server will cross-check the database contents with the contents of the Registry, reporting (and fixing) any inconsistencies it finds. You can also reconcile scopes to recover from a corrupt DHCP database. You first remove the database files, then reconcile the server's scopes.

To reconcile a single scope, follow these steps:

1. Open the DHCP snap-in by selecting Start > Administrative Tools > DHCP.

2. Expand the target server's node in the MMC until you see the target scope.

3. Right-click the target scope and choose Reconcile.

4. The Reconcile dialog box appears, but it's empty, as shown in Figure 5.15. To start the reconciliation, click the Verify button.

FIGURE 5.15 The Reconcile dialog box

1 Reconcile


This procedure compares scope information in

the database with

the registry.

Scope I IP Address


J Cancel |

5. If the database is consistent, you'll see a dialog box telling you so. If there are any inconsistencies, the dialog box will list them and allow you to repair them.

You can use a similar procedure to reconcile all scopes on a server. You just right-click the DHCP server and select Reconcile All Scopes instead of just Reconcile (which reconciles an individual scope). To recover a broken DHCP server the preferred way, you first remove the database files and then reconcile all scopes on the server to rebuild the database.

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