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V-221103

CAT II (Medium)

The Cisco BGP switch must be configured to reject inbound route advertisements for any Bogon prefixes.

Rule ID

SV-221103r1137894_rule

STIG

Cisco NX OS Switch RTR Security Technical Implementation Guide

Version

V3R4

CCIs

CCI-001368

Discussion

Accepting route advertisements for Bogon prefixes can result in the local autonomous system (AS) becoming a transit for malicious traffic as it will in turn advertise these prefixes to neighbor autonomous systems.

Check Content

Review the switch configuration to verify that it will reject BGP routes for any Bogon prefixes.

Step 1: Verify a prefix list has been configured containing the current Bogon prefixes as shown in the example below:

ip prefix-list PREFIX_FILTER seq 5 deny 0.0.0.0/8 le 32 
ip prefix-list PREFIX_FILTER seq 10 deny 10.0.0.0/8 le 32 
ip prefix-list PREFIX_FILTER seq 15 deny 100.64.0.0/10 le 32 
ip prefix-list PREFIX_FILTER seq 20 deny 127.0.0.0/8 le 32 
ip prefix-list PREFIX_FILTER seq 25 deny 169.254.0.0/16 le 32 
ip prefix-list PREFIX_FILTER seq 30 deny 172.16.0.0/12 le 32 
ip prefix-list PREFIX_FILTER seq 35 deny 192.0.2.0/24 le 32 
ip prefix-list PREFIX_FILTER seq 40 deny 192.88.99.0/24 le 32 
ip prefix-list PREFIX_FILTER seq 45 deny 192.168.0.0/16 le 32 
ip prefix-list PREFIX_FILTER seq 50 deny 198.18.0.0/15 le 32 
ip prefix-list PREFIX_FILTER seq 55 deny 198.51.100.0/24 le 32 
ip prefix-list PREFIX_FILTER seq 60 deny 203.0.113.0/24 le 32 
ip prefix-list PREFIX_FILTER seq 65 deny 224.0.0.0/4 le 32 
ip prefix-list PREFIX_FILTER seq 70 deny 240.0.0.0/4 le 32 
ip prefix-list PREFIX_FILTER seq 75 permit 0.0.0.0/0 ge 8

Step 2: Verify that the prefix list 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
 prefix-list PREFIX_FILTER in
 neighbor x.2.44.4 remote-as xx
 password 3 f07a10cb41db8bb6f8f0a340049a9b02
 address-family ipv4 unicast
 prefix-list PREFIX_FILTER in

Route Map Alternative 

Verify that the route map applied to the external neighbors references the configured Bogon prefix list shown above.

route-map FILTER_PREFIX_MAP permit 10
 match ip address prefix-list PREFIX_FILTER
…
…
…
router bgp xx
 router-id 10.1.1.1
 neighbor x.1.12.2 remote-as xx
 password 3 7b07d1b3023056a9
 address-family ipv4 unicast
 route-map FILTER_PREFIX_MAP in
 neighbor x.2.44.4 remote-as xx
 password 3 f07a10cb41db8bb6f8f0a340049a9b02
 address-family ipv4 unicast
 route-map FILTER_PREFIX_MAP in

If the switch is not configured to reject inbound route advertisements for any Bogon prefixes, this is a finding.

Fix Text

Configure the switch to reject inbound route advertisements for any Bogon prefixes.

Step 1: Configure a prefix list containing the current Bogon prefixes as shown below:

SW1(config)# ip prefix-list PREFIX_FILTER seq 5 deny 0.0.0.0/8 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 10 deny 10.0.0.0/8 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 15 deny 100.64.0.0/10 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 20 deny 127.0.0.0/8 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 25 deny 169.254.0.0/16 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 30 deny 172.16.0.0/12 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 35 deny 192.0.2.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 40 deny 192.88.99.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 45 deny 192.168.0.0/16 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 50 deny 198.18.0.0/15 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 55 deny 198.51.100.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 60 deny 203.0.113.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 65 deny 224.0.0.0/4 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 70 deny 240.0.0.0/4 le 32
SW1(config)# ip prefix-list PREFIX_FILTER seq 75 permit 0.0.0.0/0 ge 8

Step 2: Apply the prefix list filter inbound to each external BGP 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 PREFIX_FILTER in
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 PREFIX_FILTER in
SW1(config-router-neighbor-af)# end

Route Map Alternative 

Step 1: Configure the route map referencing the configured prefix list above.

SW1(config)# route-map FILTER_PREFIX_MAP permit 10
SW1(config-route-map)# match ip address prefix-list PREFIX_FILTER
SW1(config-route-map)# exit

Step 2: Apply the route-map inbound to each external BGP 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)# route-map FILTER_PREFIX_MAP in
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)# route-map FILTER_PREFIX_MAP in
SW1(config-router-neighbor-af)# end