Check: CISC-RT-000530
Cisco NX OS Switch RTR STIG:
CISC-RT-000530
(in versions v2 r3 through v1 r0.1)
Title
The Cisco BGP switch must be configured to reject outbound route advertisements for any prefixes belonging to the IP core. (Cat II impact)
Discussion
Outbound route advertisements belonging to the core can result in traffic either looping or being black holed, or at a minimum, using a non-optimized path.
Check Content
Step 1: Verify that a prefix list has been configured containing prefixes belonging to the IP core. ip prefix-list FILTER_CORE_PREFIXES seq 5 deny x.1.1.0/24 le 32 ip prefix-list FILTER _CORE_PREFIXES seq 10 deny x.1.2.0/24 le 32 ip prefix-list FILTER _CORE_PREFIXES seq 15 permit 0.0.0.0/0 ge 8 Step 2: Verify that the prefix lists has been applied to all external BGP peers as shown in the example below: router bgp xx router-id 10.1.1.1 neighbor x.1.12.2 remote-as xx password 3 7b07d1b3023056a9 address-family ipv4 unicast FILTER _CORE_PREFIXES out neighbor x.2.44.4 remote-as xx password 3 f07a10cb41db8bb6f8f0a340049a9b02 address-family ipv4 unicast prefix-list FILTER _CORE_PREFIXES out If the switch is not configured to reject outbound route advertisements for prefixes belonging to the IP core, this is a finding.
Fix Text
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 FILTER_CORE_PREFIXES deny x.1.1.0/24 le 32 SW1(config)# ip prefix-list FILTER _CORE_PREFIXES deny x.1.2.0/24 le 32 SW1(config)# ip prefix-list FILTER _CORE_PREFIXES permit 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)# router bgp xx SW1(config-router)# neighbor x.1.12.2 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# prefix-list FILTER _CORE_PREFIXES out SW1(config-router-neighbor-af)# exit SW1(config-router-neighbor)# exit SW1(config-router)# neighbor x.2.44.4 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# prefix-list FILTER _CORE_PREFIXES out SW1(config-router-neighbor-af)# end
Additional Identifiers
Rule ID: SV-221107r622190_rule
Vulnerability ID: V-221107
Group Title: SRG-NET-000205-RTR-000006
Expert Comments
CCIs
Number | Definition |
---|---|
CCI-001097 |
The information system monitors and controls communications at the external boundary of the information system and at key internal boundaries within the system. |
Controls
Number | Title |
---|---|
SC-7 |
Boundary Protection |