The Cisco 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.

An XCCDF Rule

Description

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.

ID: SV-216605r856193_rule
Version: CISC-RT-000570
Severity: Low
References: CCI-002385
Updated: about 2 months ago

Remediation Templates

This requirement is not applicable for the DODIN Backbone.

Configure the router to limit the prefix size on any route advertisement to /24 or the least significant prefixes issued to the customer.

Step 1: Configure a prefix list to reject any prefix that is longer than /24.
R1(config)#ip prefix-list FILTER_PREFIX_LENGTH permit 0.0.0.0/0 ge 8 le 24
R1(config)#ip prefix-list FILTER_PREFIX_LENGTH deny  0.0.0.0/0 le 32


Step 2: Apply the prefix list to all eBGP peers as shown in the example below.

R1(config)#router bgp xx
R1(config-router)#neighbor x.1.1.9 prefix-list FILTER_PREFIX_LENGTH in
R1(config-router)#neighbor x.2.1.7 prefix-list FILTER_PREFIX_LENGTH in

The Cisco 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.

Description

Remediation Templates

A Manual Procedure