The router must have control plane protection enabled.

From Perimeter Router Security Technical Implementation Guide Cisco

Part of Control plane protection is not enabled.

SV-21167r2_rule The router must have control plane protection enabled.

Vulnerability discussion

The Route Processor (RP) is critical to all network operations as it is the component used to build all forwarding paths for the data plane via control plane processes. It is also instrumental with ongoing network management functions that keep the routers and links available for providing network services. Hence, any disruption to the RP or the control and management planes can result in mission critical network outages. In addition to control plane and management plane traffic that is in the router’s receive path, the RP must also handle other traffic that must be punted to the RP—that is, the traffic must be fast or process switched. This is the result of packets that must be fragmented, require an ICMP response (TTL expiration, unreachable, etc.) have IP options, etc. A DoS attack targeting the RP can be perpetrated either inadvertently or maliciously involving high rates of punted traffic resulting in excessive RP CPU and memory utilization. To maintain network stability, the router must be able to securely handle specific control plane and management plane traffic that is destined to it, as well as other punted traffic. Using the ingress filter on forwarding interfaces is a method that has been used in the past to filter both forwarding path and receiving path traffic. However, this method does not scale well as the number of interfaces grows and the size of the ingress filters grow. Control plane policing can be used to increase security of routers and multilayer switches by protecting the RP from unnecessary or malicious traffic. Filtering and rate limiting the traffic flow of control plane packets can be implemented to protect routers against reconnaissance and DoS attacks allowing the control plane to maintain packet forwarding and protocol states despite an attack or heavy load on the router or multilayer switch.

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Control Plane Policing (CoPP) If supported by the router, CoPP should be used to increase security on Cisco routers by protecting the RP from unnecessary and malicious traffic. CoPP allows network operators to classify traffic based on importance that then enables the router to filter and rate limit the traffic according to the defined policy for each class. Step 1: Verify traffic types have been classified based on importance levels. The following is an example configuration: class-map match-all CoPP_CRITICAL match access-group name CoPP_CRITICAL class-map match-any CoPP_IMPORTANT match access-group name CoPP_IMPORTANT match protocol arp class-map match-all CoPP_NORMAL match access-group name CoPP_NORMAL class-map match-any CoPP_UNDESIRABLE match access-group name CoPP_UNDESIRABLE class-map match-all CoPP_DEFAULT match access-group name CoPP_DEFAULT Step 2: Review the ACLs referenced by the match access-group commands to determine if the traffic is being classified appropriately. The following is an example configuration: ip access-list extended CoPP_CRITICAL remark our control plane adjacencies are critical permit ospf host [OSPF neighbor A] any permit ospf host [OSPF neighbor B] any permit pim host [PIM neighbor A] any permit pim host [PIM neighbor B] any permit pim host [RP addr] any permit igmp any 224.0.0.0 15.255.255.255 permit tcp host [BGP neighbor] eq bgp host [local BGP addr] permit tcp host [BGP neighbor] host [local BGP addr] eq bgp deny ip any any ip access-list extended CoPP_IMPORTANT permit tcp host [TACACS server] eq tacacs any permit tcp [management subnet] 0.0.0.255 any eq 22 permit udp host [SNMP manager] any eq snmp permit udp host [NTP server] eq ntp any deny ip any any ip access-list extended CoPP_NORMAL remark we will want to rate limit ICMP traffic permit icmp any any echo permit icmp any any echo-reply permit icmp any any time-exceeded permit icmp any any unreachable deny ip any any ip access-list extended CoPP_UNDESIRABLE remark other management plane traffic that should not be received permit udp any any eq ntp permit udp any any eq snmptrap permit tcp any any eq 22 permit tcp any any eq 23 remark other control plane traffic not configured on router permit eigrp any any permit udp any any eq rip deny ip any any ip access-list extended CoPP_DEFAULT permit ip any any Note: Explicitly defining undesirable traffic with ACL entries enables the network operator to collect statistics. Excessive ARP packets can potentially monopolize Route Processor resources, starving other important processes. Currently, ARP is the only Layer 2 protocol that can be specifically classified using the match protocol command. Step 3: Review the policy-map to determine if the traffic is being policed appropriately for each classification. The following is an example configuration: policy-map CONTROL_PLANE_POLICY class CoPP_CRITICAL police 512000 8000 conform-action transmit exceed-action transmit class CoPP_IMPORTANT police 256000 4000 conform-action transmit exceed-action drop class CoPP_NORMAL police 128000 2000 conform-action transmit exceed-action drop class CoPP_UNDESIRABLE police 8000 1000 conform-action drop exceed-action drop class cp-default-in police 64000 1000 conform-action transmit exceed-action drop Step 4: Verify that the CoPP policy is enabled. The following is an example configuration: control-plane service-policy input CONTROL_PLANE_POLICY Note: Starting with IOS release 12.4(4)T, Control Plane Protection (CPPr) can be used to filter as well as police control plane traffic destined to the RP. CPPr is very similar to CoPP and has the ability to filter and police traffic using finer granularity by dividing the aggregate control plane into three separate categories: (1) host, (2) transit, and (3) CEF-exception. Hence, a separate policy-map could be configured for each traffic category. If CoPP is not supported, then the alternative would be the implementation of a receive path filter. Step 1: A receive path ACL or an inbound ACL on each interface must be configured to restrict traffic destined to the router. The IOS IP Receive ACL feature provides filtering capability explicitly for traffic that is destined for the router. Verify that the global ip receive acl statement has been configured as shown in the following example: ip receive acl 199 Note: If the platform does not support the ip receive path acl feature, an inbound ACL on each interface must be configured. Step 2: Verify that the ACL referenced by the ip receive acl statement restricts all control plane and management plane traffic. The ACL configuration should look similar to the following: access-list 199 deny ip any any fragments access-list 199 remark allow specific management plane traffic access-list 199 permit tcp [management subnet] 0.0.0.255 any eq 22 access-list 199 permit udp host [SNMP manager] any eq snmp access-list 199 permit tcp host [TACACS server] eq tacacs any access-list 199 permit udp host [NTP server] eq ntp any access-list 199 permit icmp [management subnet] 0.0.0.255 any access-list 199 remark allow specific control plane traffic access-list 199 permit ospf host [OSPF neighbor A] any access-list 199 permit ospf host [OSPF neighbor B] any access-list 199 permit pim host [PIM neighbor A] any access-list 199 permit pim host [PIM neighbor B] any access-list 199 permit pim host [RP addr] any access-list 199 permit igmp any 224.0.0.0 15.255.255.255 access-list 199 permit tcp host [BGP neighbor] eq bgp host [local BGP addr] access-list 199 permit tcp host [BGP neighbor] host [local BGP addr] eq bgp access-list 199 remark all other traffic destined to the device is dropped access-list 199 deny ip any any Note: If the Management Plane Protection (MPP) feature is enabled for an OOBM interface, there would be no purpose in filtering this traffic on the receive path. With MPP enabled, no interfaces except the management interface will accept network management traffic destined to the device. This feature also provides the capability to restrict which management protocols are allowed. See NET0992 for additional configuration information.

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Implement control plane protection by classifying traffic types based on importance levels and configure filters to restrict and rate limit the traffic punted to the route processor as according to each class.

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