STIGQter: STIG Summary: Cisco NX-OS Switch RTR Security Technical Implementation Guide Version: 2 Release: 1 Benchmark Date: 23 Apr 2021:

The Cisco BGP switch must be configured to reject inbound route advertisements from a customer edge (CE) switch for prefixes that are not allocated to that customer.

DISA Rule

SV-221105r622190_rule

Vulnerability Number

V-221105

Group Title

SRG-NET-000018-RTR-000004

Rule Version

CISC-RT-000510

Severity

CAT II

CCI(s)

• CCI-001368 - The information system enforces approved authorizations for controlling the flow of information within the system based on organization-defined information flow control policies.

Weight

10

Fix Recommendation

Configure the switch to reject inbound route advertisements from each CE switch for prefixes that are not allocated to that customer.

Step 1: Configure a prefix list for each customer containing prefixes belonging to each.

SW1(config)# ip prefix-list PREFIX_FILTER_CUST1 permit x.13.1.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER_CUST1 deny 0.0.0.0/0 ge 8
SW1(config)# ip prefix-list PREFIX_FILTER_CUST2 permit x.13.2.0/24 le 32
SW1(config)# ip prefix-list PREFIX_FILTER_CUST2 deny 0.0.0.0/0 ge 8

Step 2: Apply the prefix list filter inbound to each CE neighbor as shown in the example below:

SW1(config)# router bgp xx
SW1(config-router)# neighbor x.55.14.2
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list PREFIX_FILTER_CUST1 in
SW1(config-router-neighbor-af)# exit
SW1(config-router-neighbor)# exit
SW1(config-router)# neighbor x.55.14.4
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list PREFIX_FILTER_CUST2 in
SW1(config-router-neighbor-af)# end

Check Contents

Review the switch configuration to verify that there are ACLs defined to only accept routes for prefixes that belong to specific customers.

Step 1: Verify prefix list has been configured for each customer containing prefixes belonging to each customer as shown in the example below:

ip prefix-list PREFIX_FILTER_CUST1 seq 5 permit x.13.1.0/24 le 32
ip prefix-list PREFIX_FILTER_CUST1 seq 10 deny 0.0.0.0/0 ge 8
ip prefix-list PREFIX_FILTER_CUST2 seq 5 permit x.13.2.0/24 le 32
ip prefix-list PREFIX_FILTER_CUST2 seq 10 deny 0.0.0.0/0 ge 8

Step 2: Verify that the prefix lists has been applied to all to the applicable CE peers as shown in the example below:

router bgp xx
router-id 10.1.1.1
neighbor x.55.14.2 remote-as 64514
password 3 7b07d1b3023056a9
address-family ipv4 unicast
prefix-list FILTER_PREFIXES_CUST1 in
neighbor x.55.14.4 remote-as 64516
password 3 f07a10cb41db8bb6f8f0a340049a9b02
address-family ipv4 unicast
prefix-list FILTER_PREFIXES_CUST1 in

Note: Routes to PE-CE links within a VPN are needed for troubleshooting end-to-end connectivity across the MPLS/IP backbone. Hence, these prefixes are an exception to this requirement.

If the switch is not configured to reject inbound route advertisements from each CE switch for prefixes that are not allocated to that customer, this is a finding.

Vulnerability Number

V-221105

Documentable

False

Rule Version

CISC-RT-000510

Severity Override Guidance

Review the switch configuration to verify that there are ACLs defined to only accept routes for prefixes that belong to specific customers.

Step 1: Verify prefix list has been configured for each customer containing prefixes belonging to each customer as shown in the example below:

ip prefix-list PREFIX_FILTER_CUST1 seq 5 permit x.13.1.0/24 le 32
ip prefix-list PREFIX_FILTER_CUST1 seq 10 deny 0.0.0.0/0 ge 8
ip prefix-list PREFIX_FILTER_CUST2 seq 5 permit x.13.2.0/24 le 32
ip prefix-list PREFIX_FILTER_CUST2 seq 10 deny 0.0.0.0/0 ge 8

Step 2: Verify that the prefix lists has been applied to all to the applicable CE peers as shown in the example below:

router bgp xx
router-id 10.1.1.1
neighbor x.55.14.2 remote-as 64514
password 3 7b07d1b3023056a9
address-family ipv4 unicast
prefix-list FILTER_PREFIXES_CUST1 in
neighbor x.55.14.4 remote-as 64516
password 3 f07a10cb41db8bb6f8f0a340049a9b02
address-family ipv4 unicast
prefix-list FILTER_PREFIXES_CUST1 in

Note: Routes to PE-CE links within a VPN are needed for troubleshooting end-to-end connectivity across the MPLS/IP backbone. Hence, these prefixes are an exception to this requirement.

If the switch is not configured to reject inbound route advertisements from each CE switch for prefixes that are not allocated to that customer, this is a finding.

Check Content Reference

M

Target Key

4075

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