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.

An XCCDF Rule

Description

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.

ID: SV-221111r999720_rule
Version: CISC-RT-000570
Severity: Low
References: CCI-002385
Updated: 6 days ago

Remediation Templates

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

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.

Description

Remediation Templates

A Manual Procedure