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.

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.

NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.

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_Y24M10_STIG.zip

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-5, CAT|III, CCI|CCI-002385, Rule-ID|SV-216605r856193_rule, STIG-ID|CISC-RT-000570, STIG-Legacy|SV-105749, STIG-Legacy|V-96611, Vuln-ID|V-216605

Plugin: Cisco

Control ID: 03de81daf8e8e6219fabcd5066ec4cef0c806362946fec05ed7f7c75ab7982b7