CISC-RT-000570 - 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 - neighbor

Information

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.

Solution

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

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS_Router_Y20M07_STIG.zip

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-4, CAT|III, CCI|CCI-002385, Rule-ID|SV-105749r2_rule, STIG-ID|CISC-RT-000570, Vuln-ID|V-96611

Plugin: Cisco

Control ID: 8a32aa47bf2807b0224809ddcc8581e9a6f85beb60a4cc4998f31033bf44584f