Cisco IOS Security Configuration Guide: Securing the Data Plane, Release 12.4T
CISCO-IP-URPF-MIB Support
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Table Of Contents

CISCO-IP-URPF-MIB Support

Finding Feature Information

Contents

Prerequisites for CISCO-IP-URPF-MIB Support

Restrictions for CISCO-IP-URPF-MIB Support

Information About CISCO-IP-URPF-MIB Support

Implementation of Unicast RPF Notification

Elements of Unicast RPF Notification

Global Scalars

Global Tables

Per-Interface Statistics

Per-Interface Configuration

Drop-Rate Computation

How to Configure Unicast RPF Drop-Rate Notification

Configuring Unicast RPF Drop-Rate Notification via Syslog

Configuring Unicast RPF Drop-Rate Notification via SNMP

Verifying the Unicast RPF Configuration

Examples

Configuration Examples for CISCO-IP-URPF-MIB Support

Configuring Unicast RPF Drop-Rate Notification via Syslog: Example

Configuring Unicast RPF Drop-Rate Notification via SNMP: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for CISCO-IP-URPF-MIB Support


CISCO-IP-URPF-MIB Support

First Published: December 4, 2006
Last Updated: July 2, 2009

The CISCO-IP-URPF-MIB provides Simple Network Management Protocol (SNMP) notification when a specified drop-rate threshold on a managed device is exceeded. You use the IP Unicast Reverse Path Forwarding (RPF) feature to avert denial of service (DoS) attacks by verifying the validity of the source IP of an incoming packet. You can configure the Unicast RPF drop-rate threshold globally for a device or per interface.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 for CISCO-IP-URPF-MIB Support" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for CISCO-IP-URPF-MIB Support

•Restrictions for CISCO-IP-URPF-MIB Support

•Information About CISCO-IP-URPF-MIB Support

•How to Configure Unicast RPF Drop-Rate Notification

•Configuration Examples for CISCO-IP-URPF-MIB Support

•Additional References

•Feature Information for CISCO-IP-URPF-MIB Support

Prerequisites for CISCO-IP-URPF-MIB Support

Cisco IOS support for the CISCO-IP-URPF-MIB requires that the following features are configured on the device:

•Unicast RPF

•Cisco Express Forwarding (CEF) switching

•IP Routing

•SNMP

Restrictions for CISCO-IP-URPF-MIB Support

•Because Cisco IOS does not support Virtual Private Network (VPN) routing and forwarding- (VRF)- specific Unicast RPF counters, it does not support the following MIB objects related to VRF:

–cipUrpfIfVrfName

–cipUrpfVrfName

–cipUrpfVrfIfDrops

–cipUrpfVrfIfDiscontinuityTime

•This implementation of the CISCO-IP-URPF MIB supports only IPv4.

Information About CISCO-IP-URPF-MIB Support

To configure a notification threshold for Unicast RPF dropped packets, you should understand the following concepts:

•Implementation of Unicast RPF Notification

•Elements of Unicast RPF Notification

Implementation of Unicast RPF Notification

Unicast RPF is a security feature that verifies the validity of the source IP of an incoming packet. When a packet arrives at an interface and its source IP is unknown in the routing table or is a known bad source address, Unicast RPF drops the packet. Source IP verification is done to prevent denial of service (DoS) attacks by detecting problems with the incoming packets on an interface. However, Unicast RPF is challenging to deploy without some automated monitoring capability.

The CISCO-IP-URPF-MIB lets you specify a Unicast RPF drop-rate threshold on interfaces of a managed device, which sends an SNMP notification when the threshold is exceeded. The MIB includes objects for specifying global and per-interface drop counts and drop rates as well as a way to generate SNMP traps when the drop rate exceeds a configurable per-interface threshold.

Although you can configure some parameters globally, you must configure this feature on individual interfaces.

Elements of Unicast RPF Notification

The following elements make Unicast RPF drop-rate notification work:

•Global Scalars

•Global Tables

•Per-Interface Statistics

•Per-Interface Configuration

•Drop-Rate Computation

Global Scalars

The following global scalars affect how the MIB agent computes all drop rates and generates notifications:

•cipUrpfDropRateWindow—This object specifies the window of time in the recent past over which the computation occurs. If there was no window (that is, the window is the epoch since booting up), an identical drop count burst at a later time would produce a smaller drop rate than one occurring earlier.

•cipUrpfComputeInterval—This object specifies how often the drop-rate computation occurs.

•cipUrpfDropNotifyHoldDownTime—This object specifies the minimum time between notifications for a particular packet flow on an interface.

Global Tables

The CISCO-IP-URPF-MIB includes the following global tables:

•cipUrpfTable—This table contains global drop count and drop-rate objects per packet flow. These global rates are useful for determining quickly whether the managed device has Unicast RPF activity at a specific time.

•cipUrpfVrfTable—This table lets you index drop counters by VRF (if a VRF routing table is used to determine Unicast RPF checking). The table provides a way to index all the Unicast RPF-enabled interfaces by VRF.

Per-Interface Statistics

The following MIB objects track per-interface statistics:

•cipUrpfIfMonTable—This table contains the statistics for a particular packet flow on an interface.

•cipUrpfIfDrops—This object accumulates Unicast RPF drops on an interface. Snapshots of this value are used in the drop-rate computation. The computed drop rate is specified in the cipUrpfIfDropRate object. If Unicast RPF is configured on a subinterface, drop rates are computed.

Per-Interface Configuration

The following MIB objects enable per-interface configuration:

•cipUrpfIfDropRateNotifyEnable—This object specifies whether the system produces the cipUrpfIfDropRateNotify notification because Unicast RPF has dropped version cipUrpfIfIpVersion IP packets on the specified interface.

•cipUrpfIfNotifyDropRateThreshold—This object specifies the drop-rate threshold value above which a notification is generated.

Drop-Rate Computation

Whenever Unicast RPF is configured on an interface, the drop-rate calculation is done periodically (at intervals specified by the cipUrpfComputeInterval object). Drop rates are computed over a constantly-sliding window, which covers the period starting at the configured number of seconds before the calculation and ending with the performance of the calculation.

How to Configure Unicast RPF Drop-Rate Notification

This section contains the following procedures:

•Configuring Unicast RPF Drop-Rate Notification via Syslog

•Configuring Unicast RPF Drop-Rate Notification via SNMP

•Verifying the Unicast RPF Configuration

Configuring Unicast RPF Drop-Rate Notification via Syslog

To configure the Unicast RPF drop-rate threshold and computation parameters for notification via syslog, perform the steps in this section.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip verify drop-rate compute window seconds

4. ip verify drop-rate compute interval seconds

5. ip verify drop-rate notify hold-down seconds

6. interface type number

7. ip verify unicast notification threshold rate-val

8. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip verify drop-rate compute window seconds

Example:

Router(config)# ip verify drop-rate compute window 60

Configures the period of time, in seconds, over which the Unicast RPF drop count used in the drop-rate computation is collected.

The range is from 30 to 300. The default is 300.

Note The value for the compute window must be greater than or equal to that entered using the ip verify drop-rate compute interval command.

Step 4 

ip verify drop-rate compute interval seconds

Example:

Router(config)# ip verify drop-rate compute interval 60

Configures the interval of time, in seconds, between Unicast RPF drop-rate computations.

The range is from 30 to 300. The default is 30.

Note The value for the compute interval must be less than or equal to that entered using the ip verify drop-rate compute window command.

Step 5 

ip verify drop-rate notify hold-down seconds

Example:

Router(config)# ip verify drop-rate notify hold-down 60

Configures the minimum time, in seconds, between Unicast RPF drop-rate notifications.

The range is from 30 to 300. The default is 300.

Step 6 

interface type number

Example:

Router(config)# interface ethernet 3/0

Enters interface configuration mode.

Step 7 

ip verify unicast notification threshold rate-val

Example:

Router(config-if)# ip verify unicast notification threshold 750

Configures the threshold value, in packets per second, which determines whether to send a Unicast RPF drop-rate notification.

The range is from 0 to the maximum number of packets the interface can process in one second. The default is 1000.

Note If you configure the threshold to be 0, every packet drop triggers a notification.

Step 8 

end

Example:

Router(config-if)# end

Returns to privileged EXEC mode.

Configuring Unicast RPF Drop-Rate Notification via SNMP

To configure the Unicast RPF drop-rate threshold and computation parameters for notification via SNMP, perform the steps in this section.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip verify drop-rate compute window seconds

4. ip verify drop-rate compute interval seconds

5. ip verify drop-rate notify hold-down seconds

6. interface type number

7. ip verify unicast notification threshold rate-val

8. snmp trap ip verify drop-rate

9. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip verify drop-rate compute window seconds

Example:

Router(config)# ip verify drop-rate compute window 60

Configures the period of time, in seconds, over which the Unicast RPF drop count used in the drop-rate computation is collected.

The range is from 30 to 300. The default is 300.

Note The value for the compute window must be greater than or equal to that entered using the ip verify drop-rate compute interval command.

Step 4 

ip verify drop-rate compute interval seconds

Example:

Router(config)# ip verify drop-rate compute interval 60

Configures the interval of time, in seconds, between Unicast RPF drop-rate computations.

The range is from 30 to 300. The default is 30.

Note The value for the compute interval must be less than or equal to that entered using the ip verify drop-rate compute window command.

Step 5 

ip verify drop-rate notify hold-down seconds

Example:

Router(config)# ip verify drop-rate notify hold-down 60

Configures the minimum time, in seconds, between Unicast RPF drop-rate notifications.

The range is from 30 to 300. The default is 300.

Step 6 

interface type number

Example:

Router(config)# interface ethernet 3/0

Enters interface configuration mode.

Step 7 

ip verify unicast notification threshold rate-val

Example:

Router(config-if)# ip verify unicast notification threshold 750

Configures the threshold value, in packets per second, which determines whether to send a Unicast RPF drop-rate notification.

The range is from 0 to the maximum number of packets the interface can process in one second. The default is 1000.

Note If you configure the threshold to be 0, every packet drop triggers a notification.

Step 8 

snmp trap ip verify drop-rate

Example:

Router(config-if)# snmp trap ip verify drop-rate

Configures the router to send an SNMP notification when the Unicast RPF drop rate exceeds the configured threshold.

Step 9 

end

Example:

Router(config-if)# end

Returns to privileged EXEC mode.

Verifying the Unicast RPF Configuration

To verify the Unicast RPF configuration and troubleshoot the operation of Unicast RPF drop-rate notifications, perform the steps in this section.

SUMMARY STEPS

1. enable

2. show ip interface type number

3. debug ip verify mib

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

show ip interface type number

Example:

Router# show ip interface ethernet 3/0

Displays the verification drop rate and the number of verification drops when Unicast RPF is configured for the specified interface.

Step 3 

debug ip verify mib

Example:

Router# debug ip verify mib

Displays output useful for troubleshooting Unicast RPF notification.

Examples

The last five lines in following example show the output of the show ip interface command when Unicast RPF is configured: 

Router# show ip interface ethernet 2/3


Ethernet2/3 is up, line protocol is up

  Internet address is 10.10.5.4/16

  Broadcast address is 255.255.255.255

  Address determined by non-volatile memory

  MTU is 1500 bytes

  Helper address is not set

  Directed broadcast forwarding is disabled

  Outgoing access list is not set

  Inbound  access list is not set

  Proxy ARP is enabled

  Local Proxy ARP is disabled

  Security level is default

  Split horizon is enabled

  ICMP redirects are always sent

  ICMP unreachables are always sent

  ICMP mask replies are never sent

  IP fast switching is disabled

  IP Flow switching is disabled

  IP CEF switching is disabled

  IP Null turbo vector

  IP Null turbo vector

  IP multicast fast switching is disabled

  IP multicast distributed fast switching is disabled

  IP route-cache flags are No CEF

  Router Discovery is disabled

  IP output packet accounting is disabled

  IP access violation accounting is disabled

  TCP/IP header compression is disabled

  RTP/IP header compression is disabled

  Probe proxy name replies are disabled

  Policy routing is disabled

  Network address translation is disabled

  WCCP Redirect outbound is disabled

  WCCP Redirect inbound is disabled

  WCCP Redirect exclude is disabled

  BGP Policy Mapping is disabled

  Input features: uRPF

  IP verify source reachable-via RX, allow default

   0 verification drops

   0 suppressed verification drops

   0 verification drop-rate

Router#

The following example shows the output of the debug ip verify mib command: 

Router# debug ip verify mib


01:29:45: cipUrpfScalar_get, searchType 161

01:29:45: ipurpfmib_get_scalars

01:29:45: cipUrpfScalar_get, searchType 161

01:29:45: cipUrpfScalar_get, searchType 161

01:29:45: ipurpfmib_get_scalars

01:29:45: cipUrpfScalar_get, searchType 161

01:29:45: cipUrpfScalar_get, searchType 161

01:29:45: ipurpfmib_get_scalars

01:29:45: cipUrpfScalar_get, searchType 
161ipurpfmib_get_urpf_entryipurpfmib_get_urpf_entryipurpfmib_get_urpf_entryipurpfmib_get_ 
urpf_entry

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

01:29:45: cipUrpfIfMonEntry_get, searchType 161

01:29:45: ipurpfmib_get_urpf_ifmon_entry entry: ST 161, if 1, ip 1

Configuration Examples for CISCO-IP-URPF-MIB Support

This section provides the following configuration examples:

•Configuring Unicast RPF Drop-Rate Notification via Syslog: Example

•Configuring Unicast RPF Drop-Rate Notification via SNMP: Example

Configuring Unicast RPF Drop-Rate Notification via Syslog: Example

The following example shows how to configure Unicast RPF drop-rate notification via syslog: 

Router> enable

Router# configure terminal

Router(config)# ip verify drop-rate compute window 60

Router(config)# ip verify drop-rate compute interval 60

Router(config)# ip verify drop-rate hold-down 60

Router(config)# interface ethernet 3/0

Router(config-if)# ip verify unicast notification threshold 750

Router(config-if)# end

Configuring Unicast RPF Drop-Rate Notification via SNMP: Example

The following example shows how to configure Unicast RPF drop-rate notification via SNMP: 

Router> enable

Router# configure terminal

Router(config)# ip verify drop-rate compute window 60

Router(config)# ip verify drop-rate compute interval 60

Router(config)# ip verify drop-rate hold-down 60

Router(config)# interface ethernet 3/0

Router(config-if)# ip verify unicast notification threshold 750

Router(config-if)# snmp trap ip verify drop-rate

Router(config-if)# end

Additional References

The following sections provide references related to the CISCO-IP-URPF-MIB Support feature.

Related Documents

Related Topic
Document Title

Configuring Unicast RPF

"Configuring Unicast Reverse Path Forwarding" module in the Cisco IOS Security Configuration Guide: Securing the Data Plane

Configuring SNMP

"Configuring SNMP Support" module in the Cisco IOS Network Management Configuration Guide


Standards

Standard
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—


MIBs

MIB
MIBs Link

•CISCO-IP-URPF-MIB

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

—


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for CISCO-IP-URPF-MIB Support

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator lets you determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for CISCO-IP-URPF-MIB Support

Feature Name
Releases
Feature Information

CISCO-IP-URPF-MIB Support

12.2(31)SB2
12.2(33)SRC
12.4(20)T
12.2(33)SXI2

The CISCO-IP-URPF-MIB provides SNMP notification when a specified drop-rate threshold on a managed device is exceeded. You use the IP Unicast RPF feature to avert DoS attacks by verifying the validity of the source IP of an incoming packet. You can configure the Unicast RPF drop-rate threshold globally for a device or per interface.

The following commands were introduced or modified: debug ip verify mib, ip verify drop-rate compute interval, ip verify drop-rate compute window, ip verify drop-rate notify hold-down, ip verify unicast notification threshold, show ip interface, snmp trap ip verify drop-rate


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