The Arista 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.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-256036 | ARST-RT-000570 | SV-256036r882450_rule | CCI-002385 | low |
| 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. | ||||
| STIG | Date | |||
| Arista MLS EOS 4.X Router Security Technical Implementation Guide | 2025-02-20 | |||
Details
Check Text (C-256036r882450_chk)
This requirement is not applicable for the DODIN backbone.
Review the Arista router configuration to verify there is a filter to reject inbound route advertisements that are greater than /24 or the least significant prefixes issued to the customer, whichever is larger.
Step 1: To verify there is a filter to reject inbound route advertisements that are greater than /24 or the least significant prefixes issued to the customer, whichever is larger, execute the command "sh ip prefix-list".
ip prefix-list ADVERTISE_ROUTES deny 0.0.0.0/0 ge 25
ip prefix-list ADVERTISE_ROUTES permit 0.0.0.0/0 le 32
Step 2: Verify the prefix-list is applied in BGP process. Execute the command "sh run section router bgp".
router bgp 65000
neighbor 10.1.12.2 prefix-list ADVERTISE_ROUTES in
If the Arista router is not configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer, this is a finding.
Fix Text (F-59655r882449_fix)
This requirement is not applicable for the DODIN backbone.
Ensure all eBGP Arista routers are configured to limit the prefix size on any route advertisement to /24 or the least significant prefixes issued to the customer.
Step 1: Configure the prefix-list.
ip prefix-list ADVERTISE_ROUTES deny 0.0.0.0/0 ge 25
ip prefix-list ADVERTISE_ROUTES permit 0.0.0.0/0 le 32
Step 2: Apply the prefix-list in the BGP process inbound.
LEAF-1A(config)#router bgp 65000
LEAF-1A(config)# neighbor 10.1.12.2 prefix-list ADVERTISE_ROUTES in