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The Cisco BGP router must be configured to reject outbound route advertisements for any prefixes that do not belong to any customers or the local autonomous system (AS).
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-96953 | CISC-RT-000520 | SV-106091r1_rule | Medium |
| Description |
|---|
| 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 router within the GIG IP core could redistribute Interior Gateway Protocol (IGP) routes into BGP, thereby leaking internal routes. |
| STIG | Date |
|---|---|
| Cisco IOS XE Router RTR Security Technical Implementation Guide | 2020-06-30 |
Details
| Check Text ( C-95789r1_chk ) |
|---|
| This requirement is not applicable for the DODIN Backbone. Step 1: Verify that a prefix list has been configured containing prefixes belonging to customers as well as the local AS as shown in the example below. ip prefix-list CE_PREFIX_ADVERTISEMENTS seq 5 permit x.13.1.0/24 le 32 ip prefix-list CE_PREFIX_ADVERTISEMENTS seq 10 permit x.13.2.0/24 le 32 ip prefix-list CE_PREFIX_ADVERTISEMENTS seq 15 permit x.13.3.0/24 le 32 ip prefix-list CE_PREFIX_ADVERTISEMENTS seq 20 permit x.13.4.0/24 le 32 … … … ip prefix-list CE_PREFIX_ADVERTISEMENTS seq 80 deny 0.0.0.0/0 ge 8 Step 2: Verify that the prefix lists has been applied to all CE peers as shown in the example below. router bgp 64512 no synchronization bgp log-neighbor-changes neighbor x.12.4.14 remote-as 64514 neighbor x.12.4.14 prefix-list CE_PREFIX_ADVERTISEMENTS out neighbor x.12.4.16 remote-as 64516 neighbor x.12.4.16 prefix-list CE_PREFIX_ADVERTISEMENTS out If the router is not configured to reject outbound route advertisements that do not belong to any customers or the local AS, this is a finding. |
| Fix Text (F-102633r1_fix) |
|---|
| 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 CE_PREFIX_ADVERTISEMENTS permit x.13.1.0/24 le 32 R1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.2.0/24 le 32 R1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.3.0/24 le 32 R1(config)#ip prefix-list CE_PREFIX_ADVERTISEMENTS permit x.13.4.0/24 le 32 … … … R1(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. R1(config)#router bgp 64512 R1(config-router)#neighbor x.12.4.14 prefix-list CE_PREFIX_ADVERTISEMENTS out R1(config-router)#neighbor x.12.4.16 prefix-list CE_PREFIX_ADVERTISEMENTS out |