By default, any device with an RFC1918 IP address (included in a 10/8, 172.16/12, or 192.168/16 CIDR block) that the ExtraHop system automatically discovers is classified as an internal device. You can then monitor internal network connections to devices outside of your network with ExtraHop metrics and detections. These metrics and detections can help you determine if unauthorized devices are attempting to access your internal network. However, because some network environments include non-RFC1918 IP addresses as part of their internal network, you can change the internal or external classification for IP addresses from the Network Localities page. For example, you can specify that a remote office CIDR block contains internal IP addresses.
Here are some important considerations:
- You must have full-write privileges to change the locality of IP addresses.
- You must enter a unique range of IP addresses.
- Log into the Web UI of the Discover or Command appliance.
- Click the System Settings icon in the upper right corner of the page and click Network Localities.
- Click Add a CIDR Block.
- In the CIDR BLOCK field, type a single IP address or CIDR block.
- Select Internal or External, based on which classification you want to apply to the CIDR block.
- Optional: In the DESCRIPTION field, type information about why you are configuring the locality of this CIDR block.
- At the top of the page, click Save.
- To add more entries, click Add CIDR, select the locality, and then click Save.
Next stepsTo verify that the ExtraHop system no longer classifies an IP address as an external or internal, look at external metrics by completing the following steps:
- Click Metrics at the top of the page.
- Scroll down the page and click the TCP Devices activity group. A protocol page appears that displays metrics for every device on your network with TCP activity.
- In the TCP Connections section near the top of page, look for changes in the External Accepted and External Connected metrics. For example, if you classified a large CIDR block for a remote office as Internal, then the number of external connections should be lower.