CISC-RT-000520 - The Cisco BGP switch must be configured to reject outbound route advertisements for any prefixes that do not belong to any customers or the local autonomous system (AS).

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Information

Advertisement of routes by an autonomous system for networks that do not belong to any of its customers pulls traffic away from the authorized network. This causes a denial of service (DoS) on the network that allocated the block of addresses and may cause a DoS on the network that is inadvertently advertising it as the originator. It is also possible that a misconfigured or compromised switch within the GIG IP core could redistribute Interior Gateway Protocol (IGP) routes into BGP, thereby leaking internal routes.

Solution

Step 1: Configure a prefix list for containing all customer and local AS prefixes as shown in the example below:

SW1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.1.0/24 le 32
SW1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.2.0/24 le 32
SW1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.3.0/24 le 32
SW1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.4.0/24 le 32
...
...
...
SW1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS deny 0.0.0.0/0 ge 8

Step 2: Apply the prefix list filter outbound to each CE neighbor as shown in the example.

SW1(config)#router bgp 64512
SW1(config-switch)#neighbor x.12.4.14 prefix-list CE_PREFIX_ADVERTISEMENTS out
SW1(config-switch)#neighbor x.12.4.16 prefix-list CE_PREFIX_ADVERTISEMENTS out

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS-XE_Switch_Y24M04_STIG.zip

Item Details

References: CAT|II, CCI|CCI-001368, Rule-ID|SV-221026r622190_rule, STIG-ID|CISC-RT-000520, STIG-Legacy|SV-110873, STIG-Legacy|V-101769, Vuln-ID|V-221026

Plugin: Cisco

Control ID: 267b76a3222e56bb0785c1bfe651a8368552068aad7e26b5e7e11ecd7ff6fc5b