Detections
Analytics
CISC-RT-000570 - The Cisco BGP switch 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 switch performance due to the size of routing tables and also result in black-holing legitimate traffic. Initiated by an attacker or a misconfigured switch, prefix de-aggregation occurs when the announcement of a large prefix is fragmented into a collection of smaller prefix announcements.Solution
Configure the switch 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.
SW1(config)# ip prefix-list FILTER_PREFIX_LENGTH permit 0.0.0.0/0 ge 8 le 24
SW1(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:
SW1(config)# router bgp xx
SW1(config-router)# neighbor x.1.12.2
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list FILTER_PREFIX_LENGTH in
SW1(config-router-neighbor-af)# exit
SW1(config-router-neighbor)# exit
SW1(config-router)# neighbor x.2.44.4
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list FILTER_PREFIX_LENGTH in
SW1(config-router-neighbor-af)# end
See Also
https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_NX-OS_Switch_Y26M01_STIG.zip
Item Details
Audit Name: DISA Cisco NX OS Switch RTR STIG v3r3
Category: SYSTEM AND COMMUNICATIONS PROTECTION
References: 800-53|SC-5, CAT|III, CCI|CCI-002385, Rule-ID|SV-221111r999720_rule, STIG-ID|CISC-RT-000570, STIG-Legacy|SV-111041, STIG-Legacy|V-101937, Vuln-ID|V-221111
Plugin: Cisco
Control ID: 27ec420bb07b848ebd49708574a27e1c4f5115543b6a14af0ac2e452aae466cb