The Dell OS10 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-269891 | OS10-RTR-000680 | SV-269891r1052058_rule | CCI-002385 | low |
| Description | ||||
| The effects of prefix deaggregation 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 deaggregation occurs when the announcement of a large prefix is fragmented into a collection of smaller prefix announcements. | ||||
| STIG | Date | |||
| Dell OS10 Switch Router Security Technical Implementation Guide | 2024-12-11 | |||
Details
Check Text (C-269891r1052058_chk)
This requirement is not applicable for the DODIN Backbone.
Review the router configuration to verify that 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.
The prefix filter must be referenced outbound on the appropriate BGP neighbor statements.
Step 1: Verify prefix lists have been configured for each customer containing prefixes that belong to that customer.
OS10# show running-configuration prefix-list
!
ip prefix-list LONG_PREFIX_FILTER permit 0.0.0.0/0 ge 8 le 24
ip prefix-list LONG_PREFIX_FILTER deny 0.0.0.0/0
Step 2: Verify the route map applied to the external neighbors references the configured prefix list shown above.
OS10# show running-configuration route-map
!
route-map LONG_PREFIX_FILTER_MAP permit 50
match ip address prefix-list LONG_PREFIX_FILTER
Step 3: Verify the route map applied to the external neighbors references the appropriate route maps shown above.
!
router bgp 10
!
neighbor 50.1.1.1
!
address-family ipv4 unicast
route-map LONG_PREFIX_FILTER_MAP in
If the 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-73825r1052057_fix)
Ensure all eBGP 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 a prefix list for each customer containing prefixes belonging to each.
OS10(config)# ip prefix-list LONG_PREFIX_FILTER permit 0.0.0.0/0 ge 8 le 24
OS10(config)# ip prefix-list LONG_PREFIX_FILTER deny 0.0.0.0/0
Step 2: Configure the route map referencing the configured prefix list.
OS10(config)# route-map LONG_PREFIX_FILTER_MAP 50
OS10(config-route-map)# match ip address prefix-list LONG_PREFIX_FILTER
OS10(config-route-map)# exit
Step 3: Apply the route-map outbound to each external BGP neighbor.
OS10(config)# router bgp 10
OS10(config-router-bgp-10)# neighbor 50.1.1.1
OS10(config-router-neighbor)# address-family ipv4 unicast
OS10(config-router-bgp-neighbor-af)# route-map LONG_PREFIX_FILTER_MAP in
OS10(config-router-bgp-neighbor-af)# exit
OS10(config-router-neighbor)# exit
OS10(config-router-bgp-10)# exit