V-273635

Discussion

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.

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This requirement is not applicable for the DODIN Backbone.

Review the router configuration to determine if it is compliant with this requirement.

1. Verify a route filter has been configured to reject prefixes longer than /24, or the least significant prefixes issued to the customers as shown in the example below:
ip prefix-list FILTER_PREFIX_LENGTH seq 5 permit 0.0.0.0/0 ge 8 le 24
ip prefix-list FILTER_PREFIX_LENGTH seq 10 deny 0.0.0.0/0 le 32

2. Verify prefix filtering has been applied to each eBGP peer as shown in the following example:
router bgp
neighbor x.1.1.9 remote-as yy
neighbor x.1.1.9 prefix-list FILTER_PREFIX_LENGTH 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.