The Cisco perimeter router must be configured to protect an enclave connected to an alternate gateway by using an inbound filter that only permits packets with destination addresses within the sites address space.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216756	CISC-RT-000280	SV-216756r531087_rule		High

Description
Enclaves with alternate gateway connections must take additional steps to ensure there is no compromise on the enclave network or NIPRNet. Without verifying the destination address of traffic coming from the site's alternate gateway, the perimeter router could be routing transit data from the Internet into the NIPRNet. This could also make the perimeter router vulnerable to a denial-of-service (DoS) attack as well as provide a back door into the NIPRNet. The DoD enclave must ensure the ingress filter applied to external interfaces on a perimeter router connecting to an Approved Gateway is secure through filters permitting packets with a destination address belonging to the DoD enclave's address block.

Description

Enclaves with alternate gateway connections must take additional steps to ensure there is no compromise on the enclave network or NIPRNet. Without verifying the destination address of traffic coming from the site's alternate gateway, the perimeter router could be routing transit data from the Internet into the NIPRNet. This could also make the perimeter router vulnerable to a denial-of-service (DoS) attack as well as provide a back door into the NIPRNet. The DoD enclave must ensure the ingress filter applied to external interfaces on a perimeter router connecting to an Approved Gateway is secure through filters permitting packets with a destination address belonging to the DoD enclave's address block.

STIG	Date
Cisco IOS XR Router RTR Security Technical Implementation Guide	2024-06-06

Details

Check Text ( C-17988r507359_chk )
This requirement is not applicable for the DODIN Backbone. Step 1: Verify the interface connecting to ISP has an inbound ACL as shown in the example below. interface GigabitEthernet0/0/0/2 description Link to ISP ipv4 address x.22.1.15 255.255.255.252 ipv4 access-group ISP_ACL_INBOUND ingress Step 2: Verify that the ACL only allows traffic to specific destination addresses (i.e. enclave’s NIPRNet address space) as shown in the example below. ipv4 access-list ISP_ACL_INBOUND 10 permit tcp any any established 20 permit icmp host x.12.1.16 host x.12.1.17 echo 30 permit icmp host x.12.1.16 host x.12.1.17 echo-reply 40 permit tcp any host x.12.1.22 eq www 50 permit tcp any host x.12.1.23 eq www 60 permit esp any host x.12.1.24 70 permit ahp any host x.12.1.24 80 deny ipv4 any any log-input Note: An Approved Gateway (AG) is any external connection from a DoD NIPRNet enclave to an Internet Service Provider, or network owned by a contractor, or non-DoD federal agency that has been approved by either the DoD CIO or the DoD Component CIO. This AG requirement does not apply to commercial cloud connections when the Cloud Service Provider (CSP) network is connected via the NIPRNet Boundary Cloud Access Point (BCAP). If the ingress ACL bound to the interface connecting to an alternate gateway permits packets with addresses other than those specified, such as destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider, this is a finding.

Check Text ( C-17988r507359_chk )

This requirement is not applicable for the DODIN Backbone.

Step 1: Verify the interface connecting to ISP has an inbound ACL as shown in the example below.

interface GigabitEthernet0/0/0/2
description Link to ISP
ipv4 address x.22.1.15 255.255.255.252
ipv4 access-group ISP_ACL_INBOUND ingress

Step 2: Verify that the ACL only allows traffic to specific destination addresses (i.e. enclave’s NIPRNet address space) as shown in the example below.

ipv4 access-list ISP_ACL_INBOUND
10 permit tcp any any established
20 permit icmp host x.12.1.16 host x.12.1.17 echo
30 permit icmp host x.12.1.16 host x.12.1.17 echo-reply
40 permit tcp any host x.12.1.22 eq www
50 permit tcp any host x.12.1.23 eq www
60 permit esp any host x.12.1.24
70 permit ahp any host x.12.1.24
80 deny ipv4 any any log-input

Note: An Approved Gateway (AG) is any external connection from a DoD NIPRNet enclave to an Internet Service Provider, or network owned by a contractor, or non-DoD federal agency that has been approved by either the DoD CIO or the DoD Component CIO. This AG requirement does not apply to commercial cloud connections when the Cloud Service Provider (CSP) network is connected via the NIPRNet Boundary Cloud Access Point (BCAP).

If the ingress ACL bound to the interface connecting to an alternate gateway permits packets with addresses other than those specified, such as destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider, this is a finding.

Fix Text (F-17986r507360_fix)
This requirement is not applicable for the DODIN Backbone. Step 1: Configure the ingress ACL of the perimeter router connected to an alternate gateway to only permit packets with destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider as shown in the example below. RP/0/0/CPU0:R2(config)#ip access-list ISP_ACL_INBOUND RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any any established RP/0/0/CPU0:R2(config-ipv4-acl)#permit icmp host x.12.1.16 host x.12.1.17 echo RP/0/0/CPU0:R2(config-ipv4-acl)#permit icmp host x.12.1.16 host x.12.1.17 echo-reply RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any host x.12.1.22 eq www RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any host x.12.1.23 eq www RP/0/0/CPU0:R2(config-ipv4-acl)#permit 50 any host x.12.1.24 RP/0/0/CPU0:R2(config-ipv4-acl)#permit 51 any host x.12.1.24 RP/0/0/CPU0:R2(config-ipv4-acl)#deny ip any any log-input RP/0/0/CPU0:R2(config-ipv4-acl)#end Step 2: Apply the ACL inbound on the ISP-facing interface. RP/0/0/CPU0:R3(config)#int g0/0/0/2 RP/0/0/CPU0:R3(config-if)#ipv4 access-group ISP_ACL_INBOUND in RP/0/0/CPU0:R3(config-if)#end

Fix Text (F-17986r507360_fix)

This requirement is not applicable for the DODIN Backbone.

Step 1: Configure the ingress ACL of the perimeter router connected to an alternate gateway to only permit packets with destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider as shown in the example below.

RP/0/0/CPU0:R2(config)#ip access-list ISP_ACL_INBOUND
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any any established
RP/0/0/CPU0:R2(config-ipv4-acl)#permit icmp host x.12.1.16 host x.12.1.17 echo
RP/0/0/CPU0:R2(config-ipv4-acl)#permit icmp host x.12.1.16 host x.12.1.17 echo-reply
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any host x.12.1.22 eq www
RP/0/0/CPU0:R2(config-ipv4-acl)#permit tcp any host x.12.1.23 eq www
RP/0/0/CPU0:R2(config-ipv4-acl)#permit 50 any host x.12.1.24
RP/0/0/CPU0:R2(config-ipv4-acl)#permit 51 any host x.12.1.24
RP/0/0/CPU0:R2(config-ipv4-acl)#deny ip any any log-input
RP/0/0/CPU0:R2(config-ipv4-acl)#end

Step 2: Apply the ACL inbound on the ISP-facing interface.

RP/0/0/CPU0:R3(config)#int g0/0/0/2
RP/0/0/CPU0:R3(config-if)#ipv4 access-group ISP_ACL_INBOUND in
RP/0/0/CPU0:R3(config-if)#end