The BGP router must be configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer.

Associated with: CCI-002385

SV-92987r1_rule The BGP router must be configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer.

Vulnerability discussion

The effects of prefix de-aggregation can degrade router performance due to the size of routing tables and also result in black-holing legitimate traffic. Initiated by an attacker or a misconfigured router, prefix de-aggregation occurs when the announcement of a large prefix is fragmented into a collection of smaller prefix announcements.

Check content

Review the router configuration to verify that there is a filter to reject inbound route advertisements that are greater than /24 or the least significant prefixes issued to the customer, whichever is larger. If the router is not configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer, this is a finding.

Fix text

Ensure all eBGP routers are configured to limit the prefix size on any route advertisement to /24 or the least significant prefixes issued to the customer.

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