QoS: Policing and Shaping Configuration Guide, Cisco IOS XE 16 (Cisco ASR 920 Series)
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The Control Plane Policing feature allows you to configure a quality of service (QoS) filter that manages the traffic flow
of control plane packets to protect the control plane of
routers and switches against reconnaissance and denial-of-service (DoS) attacks. In this way, the control plane (CP) can
help maintain packet forwarding and protocol states despite an attack or heavy traffic load on the router or switch.
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see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module,
and to see a list of the releases in which each feature is supported, see the feature information table.
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Restrictions for Control
Plane Policing
Input Rate-Limiting
Support
Input rate-limiting
is performed in silent (packet discard) mode. Silent mode enables a router to
silently discard packets using policy maps applied to input control plane
traffic with the
service-policyinput command. For more information, see the
“Input Rate-Limiting and Silent Mode Operation” section.
MQC Restrictions
The Control Plane Policing feature requires the Modular QoS CLI (MQC) to configure packet classification and traffic policing.
All restrictions that apply when you use the MQC to configure traffic policing also apply when you configure control plane
policing.
Match Criteria
Support
Only the extended
IP access control lists (ACLs) classification (match) criteria is supported.
Information About Control Plane Policing
Benefits of Control Plane Policing
Configuring the Control Plane Policing feature on your Cisco router or switch provides the following benefits:
Protection against DoS attacks at infrastructure routers and switches
QoS control for packets that are destined to the control plane of Cisco routers or switches
Ease of configuration for control plane policies
Better platform reliability and availability
Control Plane Terms to
Understand
On the router, the
following terms are used for the Control Plane Policing feature:
Control plane—A
collection of processes that run at the process level on the Route Processor
(RP). These processes collectively provide high-level control for most Cisco
IOS XE functions. The traffic sent to or sent by the control plane is called
control traffic.
Forwarding
plane—A device that is responsible for high-speed forwarding of IP packets. Its
logic is kept simple so that it can be implemented by hardware to do fast
packet-forwarding. It punts packets that require complex processing (for
example, packets with IP options) to the RP for the control plane to process
them.
Control Plane Policing
Overview
To protect the control plane on a router from DoS attacks and to provide fine-control over the traffic to the control plane,
the Control Plane Policing feature treats the control plane as a separate entity with its own interface for ingress (input)
and egress (output) traffic. This interface is called the punt or inject interface, and it is similar to a physical interface
on the router. Along this interface, packets are punted from the forwarding plane to the RP (in the input direction) and injected
from the RP to the forwarding plane (in the output direction). A set of quality of service (QoS) rules can be applied on this
interface (in the input direction) in order to achieve CoPP.
These QoS rules are
applied only after the packet has been determined to have the control plane as
its destination. You can configure a service policy (QoS policy map) to prevent
unwanted packets from progressing after a specified rate limit has been
reached; for example, a system administrator can limit all TCP/TELNET packets
that are destined for the control plane.
You can use the platform qos-feature copp-mpls enable command to enable the Control Plane Policing feature on the device for MPLS explicit null scenario, control packets destined
to the device is punted to proper control CPU Q. If CoPP-MPLS remains disabled, then self destined control packets like BGP,
LDP, telnet and so on, that are MPLS explicit null tagged are not classified by CoPP and is punted to HOST_Q instead of CFM_Q/CONTROL_Q.
Note
The command platform qos-feature copp-mpls enable is supported only on Cisco ASR 920 platform.
Figure 1. Abstract Illustration of a
Router with a Single RP and Forwarding Plane
The figure provides an abstract illustration of the router with a single RP and forwarding plane. Packets that are destined
to the control plane come in through the carrier card and then go through the forwarding plane before being punted to the
RP. When an input QoS policy map is configured on the control plane, the forwarding plane performs the QoS action (for example,
a transmit or drop action) before punting packets to the RP in order to achieve the best protection of the control plane in
the RP.
Note
The figure is not applicable to the RSP3 module.
Note
As mentioned in this section, the control plane interface is directly connected to the RP, so all traffic through the control
plane interface to or from the control-plane is not subject to the CoPP function performed by the forwarding plane.
Supported
Protocols
The following table lists the
protocols supported on Control Plane Policing feature.
RADIUS - Remote Authentication Dial In User Service
IP/Port Match
permit udp 64.202.160.0 0.0.1.255 eq 1645 any
permit udp 64.202.160.0 0.0.1.255 any eq 1645
permit udp 64.202.160.0 0.0.1.255 eq 1646 any
permit udp 64.202.160.0 0.0.1.255 any eq 1646
permit udp 64.202.160.0 0.0.1.255 eq 1812 any
permit udp 64.202.160.0 0.0.1.255 any eq 1812
permit udp 64.202.160.0 0.0.1.255 eq 1813 any
permit udp 64.202.160.0 0.0.1.255 any eq 1813
permit tcp 64.202.160.0 0.0.1.255 eq 1645 any
permit tcp 64.202.160.0 0.0.1.255 any eq 1645
permit tcp 64.202.160.0 0.0.1.255 eq 1646 any
permit tcp 64.202.160.0 0.0.1.255 any eq 1646
permit tcp 64.202.160.0 0.0.1.255 eq 1812 any
permit tcp 64.202.160.0 0.0.1.255 any eq 1812
permit tcp 64.202.160.0 0.0.1.255 eq 1813 any
permit tcp 64.202.160.0 0.0.1.255 any eq 1813
NQ_CPU_HOST_Q
HSRP - Hot Standby Router Protocol
IP/Port Match
permit udp any 224.0.0.0/24 eq 1985
permit udp any eq 1985 224.0.0.0/24
NQ_CPU_HOST_Q
Input Rate-Limiting and
Silent Mode Operation
A router is
automatically enabled to silently discard packets when you configure input
policing on control plane traffic using the
service-policyinputpolicy-map-name
command.
Rate-limiting
(policing) of input traffic from the control plane is performed in silent mode.
In silent mode, a router that is running Cisco IOS XE software operates without
receiving any system messages. If a packet that is entering the control plane
is discarded for input policing, you do not receive an error message.
How to Use Control Plane Policing
Defining Control Plane Services
Perform this task to define control plane services, such as packet rate control and silent packet discard for the RP.
Before you begin
Before you enter control-plane configuration mode to attach an existing QoS policy to the control plane, you must first create
the policy using MQC to define a class map and policy map for control plane traffic.
Platform-specific restrictions, if any, are checked when the service policy is applied to the control plane interface.
Input policing does not provide any performance benefits. It simply controls the information that is entering the device.
Procedure
Step 1
enable
Example:
Device> enable
Enables privileged EXEC mode.
Enter your password if prompted.
Step 2
configureterminal
Example:
Device# configure terminal
Enters global configuration mode.
Step 3
control-plane
Example:
Device(config)# control-plane
Enters control-plane configuration mode (which is a prerequisite for defining control plane services).
police cir 10000000 bc 8000 pir 12000000 be 8000 conform-action transmit exceed-action transmit violate-action drop
Configure a traffic policer based on the traffic rate or committed information rate (CIR). By default, no policer is defined.
rate-bps—Specifies average traffic rate in bits per second (b/s). The range is 64000 to 10000000000. Supply an optional postfix (K,
M, G). Decimal point is allowed.
cir—Specifies a committed information rate (CIR).
cir-bps—Specifies a CIR in bits per second (b/s). The range is 64000 to 10000000000. Supply an optional postfix (K, M, G). Decimal
point is allowed.
beburst-bytes—(Optional) Specifies the conformed burst (be) or the number of acceptable burst bytes. The range is 8000 to 16000000.
conform-actionaction— (Optional) Specifies action to take on packets that conform to the specified rate limit.
pirpir-bps—(Optional) Specifies the peak information rate (PIR).
Note
cir percentpercent option is not supported on the router.
Step 10
exit
Example:
Device(config-pmap-c-police)# exit
Exits policy-map class police configuration mode
Step 11
exit
Example:
Device(config-pmap-c)# exit
Exits policy-map class configuration mode
Step 12
exit
Example:
Device(config-pmap)# exit
Exits policy-map configuration mode
Step 13
control-plane
Example:
Device(config)# control-plane
Enters control plane configuration mode.
Step 14
service-policyinputpolicy-map-name
Example:
Device(config-cp)# service-policy input Policy1
Attaches a policy map to a control plane.
Step 15
exit
Example:
Device(config-cp)# exit
Exits control plane configuration mode and returns to global configuration mode.
Step 16
exit
Example:
Device(config)# exit
Exits global configuration mode returns to privileged EXEC mode.
Configuration Examples for Control Plane Policing
Example: Configuring Control
Plane Policing on Input Telnet Traffic
! Rate-limit all other Telnet traffic.
Device(config)# access-list 140 permit tcp any any eq telnet
! Define class-map "telnet-class."
Device(config)# class-map telnet-class
Device(config-cmap)# match access-group 140
Device(config-cmap)# exit
Device(config)# policy-map control-plane-in
Device(config-pmap)# class telnet-class
Device(config-pmap-c)# police 80000 conform transmit exceed drop
Device(config-pmap-c)# exit
Device(config-pmap)# exit
! Define aggregate control plane service for the active route processor.
Device(config)# control-plane
Device(config-cp)# service-policy input control-plane-in
Device(config-cp)# end
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The following table
provides release information about the feature or features described in this
module. This table lists only the software release that introduced support for
a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature
Navigator to find information about platform support and Cisco software image
support. To access Cisco Feature Navigator, go to
www.cisco.com/go/cfn.
An account on Cisco.com is not required.
Table 1. Feature Information for
Control Plane Policing
Feature
Name
Releases
Feature
Information
Control
Plane Policing
Cisco IOS XE Release 3.14.0S
This feature was introduced on the
Cisco ASR 920 Series Aggregation Services Router
(ASR-920-12CZ-A, ASR-920-12CZ-D, ASR-920-4SZ-A, ASR-920-4SZ-D, ASR-920-10SZ-PD,
ASR-920-24SZ-IM, ASR-920-24SZ-M, ASR-920-24TZ-M).
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