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CISC-RT-000120 - The Cisco switch must be configured to protect against or limit the effects of denial-of-service (DoS) attacks by employing control plane protection.

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Information

The Route Processor (RP) is critical to all network operations because 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 switches and links available for providing network services. Any disruption to the RP or the control and management planes can result in mission-critical network outages.

A DoS attack targeting the RP can result in excessive CPU and memory utilization. To maintain network stability and RP security, the switch must be able to handle specific control plane and management plane traffic that is destined to the RP. In the past, one method of filtering was to use ingress filters on forwarding interfaces 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 grows. Control plane policing increases the security of switches 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 switches against reconnaissance and DoS attacks, allowing the control plane to maintain packet forwarding and protocol states despite an attack or heavy load on the switch or multilayer switch.

Solution

Configure the Cisco switch protect against known types of DoS attacks on the route processor. Implementing a CoPP policy as shown in the example below is a best practice method.

Step 1: Configure ACLs specific traffic types.

SW1(config)# ip access-list CoPP_CRITICAL
SW1(config-acl)# remark our control plane adjacencies are critical
SW1(config-acl)# permit ospf host 10.1.12.1 any
SW1(config-acl)# permit ospf host 10.1.22.1 any
SW1(config-acl)# permit pim host 10.1.12.1 any
SW1(config-acl)# permit pim host 10.1.22.1 any
SW1(config-acl)# permit pim host 10.1.33.4 any
SW1(config-acl)# permit igmp any 224.0.0.0 15.255.255.255
SW1(config-acl)# permit tcp host 10.2.33.3 eq bgp host 10.2.33.4
SW1(config-acl)# permit tcp host 10.2.33.3 host 10.2.33.4 eq bgp
SW1(config-acl)# deny ip any any
SW1(config-acl)# exit

SW1(config)# ip access-list CoPP_IMPORTANT
SW1(config-acl)# permit tcp host 10.1.33.5 eq tacacs any
SW1(config-acl)# permit tcp 10.1.33.0 0.0.0.255 any eq 22
SW1(config-acl)# permit udp host 10.1.33.7 any eq snmp
SW1(config-acl)# permit udp host 10.1.33.9 eq ntp any
SW1(config-acl)# deny ip any any
SW1(config-acl)# exit

SW1(config)# ip access-list CoPP_NORMAL
SW1(config-acl)# remark we will want to rate limit ICMP traffic
SW1(config-acl)# permit icmp any any echo
SW1(config-acl)# permit icmp any any echo-reply
SW1(config-acl)# permit icmp any any time-exceeded
SW1(config-acl)# permit icmp any any unreachable
SW1(config-acl)# deny ip any any
SW1(config-acl)# exit

SW1(config)# ip access-list CoPP_UNDESIRABLE
SW1(config-acl)# remark other management plane traffic that should not be received
SW1(config-acl)# permit udp any any eq ntp
SW1(config-acl)# permit udp any any eq snmp
SW1(config-acl)# permit tcp any any eq 22
SW1(config-acl)# permit tcp any any eq 23
SW1(config-acl)# remark other control plane traffic not configured on switch
SW1(config-acl)# permit eigrp any any
SW1(config-acl)# permit udp any any eq rip
SW1(config-acl)# deny ip any any
SW1(config-acl)# exit

SW1(config)# ip access-list CoPP_DEFAULT
SW1(config-acl)# permit ip any any
SW1(config-acl)# exit

Step 2: Configure class maps referencing each of the ACLs.

SW1(config)# class-map match-all CoPP_CRITICAL
SW1(config-cmap)# match access-group name CoPP_CRITICAL
SW1(config-cmap)# class-map match-any CoPP_IMPORTANT
SW1(config-cmap)# match access-group name CoPP_IMPORTANT
SW1(config-cmap)# match protocol arp
SW1(config-cmap)# class-map match-all CoPP_NORMAL
SW1(config-cmap)# match access-group name CoPP_NORMAL
SW1(config-cmap)# class-map match-any CoPP_UNDESIRABLE
SW1(config-cmap)# match access-group name CoPP_UNDESIRABLE
SW1(config-cmap)# class-map match-all CoPP_DEFAULT
SW1(config-cmap)# match access-group name CoPP_DEFAULT
SW1(config-cmap)# exit

Step 3: Configure a policy map referencing the configured class maps and apply appropriate bandwidth allowance and policing attributes.

SW1(config)# policy-map CONTROL_PLANE_POLICY
SW1(config-pmap)# class CoPP_CRITICAL
SW1(config-pmap-c)# police 512000 8000 conform-action transmit exceed-action transmit
SW1(config-pmap-c-police)# class CoPP_IMPORTANT
SW1(config-pmap-c)# police 256000 4000 conform-action transmit exceed-action drop
SW1(config-pmap-c-police)# class CoPP_NORMAL
SW1(config-pmap-c)# police 128000 2000 conform-action transmit exceed-action drop
SW1(config-pmap-c-police)# class CoPP_UNDESIRABLE
SW1(config-pmap-c)# police 8000 1000 conform-action drop exceed-action drop
SW1(config-pmap-c-police)# class CoPP_DEFAULT
SW1(config-pmap-c)# police 64000 1000 conform-action transmit exceed-action drop
SW1(config-pmap-c-police)# exit
SW1(config-pmap-c)# exit
SW1(config-pmap)# exit

Step 4: Apply the policy map to the control plane.

SW1(config)# control-plane
SW1(config-cp)# service-policy input CONTROL_PLANE_POLICY
SW1(config-cp)# end

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_NX-OS_Switch_STIG.zip

Item Details

Category: CONFIGURATION MANAGEMENT

References: 800-53|CM-6, CAT|II, CCI|CCI-002385, CSCv6|3.1, Rule-ID|SV-110977r1_rule, STIG-ID|CISC-RT-000120, Vuln-ID|V-101873

Plugin: Cisco

Control ID: f35be647de8f1765ba12463822af4fb6c6a2cfbee15714c55a15dae1102ee464