Finding ID | Version | Rule ID | IA Controls | Severity |
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V-96603 | CISC-RT-000530 | SV-105741r1_rule | Medium |
Description |
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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. |
STIG | Date |
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Cisco IOS Router RTR Security Technical Implementation Guide | 2020-06-30 |
Check Text ( C-95439r1_chk ) |
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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 no synchronization bgp log-neighbor-changes neighbor x.1.4.12 remote-as yy neighbor x.1.4.12 prefix-list FILTER _CORE_PREFIXES out If the router is not configured to reject outbound route advertisements for prefixes belonging to the IP core, this is a finding. |
Fix Text (F-102277r1_fix) |
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Step 1: Configure a prefix list for containing all customer and local AS prefixes as shown in the example below. R1(config)#ip prefix-list FILTER_CORE_PREFIXES deny x.1.1.0/24 le 32 R1(config)#ip prefix-list FILTER _CORE_PREFIXES deny x.1.2.0/24 le 32 R1(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. R1(config)#router bgp xx R1(config-router)#neighbor x.1.4.12 prefix-list FILTER _CORE_PREFIXES out |