Detections
Analytics
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).
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 below:
SW1(config)#switch 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_NX-OS_Switch_Y26M01_STIG.zip
Item Details
Audit Name: DISA Cisco NX OS Switch RTR STIG v3r3
Category: ACCESS CONTROL
References: 800-53|AC-4, CAT|II, CCI|CCI-001368, Rule-ID|SV-221106r999715_rule, STIG-ID|CISC-RT-000520, STIG-Legacy|SV-111031, STIG-Legacy|V-101927, Vuln-ID|V-221106
Plugin: Cisco
Control ID: 3b2d2c3835d3dd56fccd0c4aa5d400774b7485f8eb75b7418c97c1a7d2575259